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A pinboard by
usha Kiranmayee

VISITING SCIENTIST, ICRISAT

PINBOARD SUMMARY

shoot fly resistance and stay-green traits of sorghum were mainley focused

Sorghum is the dryland cereal crop serving as food, fodder, fuel. Both biotic and abiotic stresses affect the sorghum crop productivity and these are major constraints for sorghum yield. In order to overcome these stresses, there is a need to develop biotic and abiotic stress tolerant varieties for increase productivity under increased demand for food under varied climatic conditions. An introgression line cross was developed having biotic (shoot fly) resistant donor one with abiotic (drought/stay-green) resistant donor. Shoot fly resistance QTLs and stay-green QTLs were overlapping on sorghum chromosome SBI-10. In order to fine map, those QTLs F2 fine mapping population was developed and based on SSR molecular markers 2000 F2 genotypes were reduced to 152 recombinant genotypes. All the 152 selected F2 s were phenotyped for two different seasons for shoot fly resistance and stay-green and the same genotypes were generated with SNPs. Identified nearly 15000 SNPs and utilized 260 SNPs for fine mapping the shoot fly resistance QTLs and stay-green QLs on SBI-10. With the help of these SNPs 2mb genomic regions were now fine mapped to 100-400kb. SNPs identified in the fine mapped region were utilized in molecular marker-assisted breeding programs of sorghum. We have identified few recombinants with high yield with resistance to both shoot fly and drought were identified. Those step introgression lines can be studied at expression level and then again phenotyped for evaluating their performance under different environmental conditions. Putative candidate genes identified in the fine mapped region with help of functional annotation. senescence-associated protein, gossy15, AP2 transcription factors, NAC transcription factors were identified which have previous reports in stay-green and shoot fly tolerance mechanisms. Furthur expression studied of candidate genes and KASPer assay (SNP genotyping) will reveal the functional candidate genes and their affecting pathways. A 3 gene cassette will be released in a single variety with SNP genotyping detection methods. A buy 1 get 2 offer will be going to arrive for farmers soon with biotic stress tolerance+ abiotic stress tolerance + high yield. Farmer is the king ultimately our goal is to benefit poor farmers and feed the hungry world under global warming conditions also.

25 ITEMS PINNED

Evaluation of QTLs for Shoot Fly ( Atherigona soccata ) Resistance Component Traits of Seedling Leaf Blade Glossiness and Trichome Density on Sorghum ( Sorghum bicolor ) Chromosome SBI-10L

Abstract: Abstract Shoot fly is a major insect pest of sorghum damaging early crop growth, establishment and productivity. Host plant resistance is an efficient approach to minimize yield losses due to shoot fly infestation. Seedling leaf blade glossiness and trichome density are morphological traits associated with shoot fly resistance. Our objective was to identify and evaluate QTLs for glossiness and trichome density using- i) 1894 F2s, ii) a sub-set of 369 F2-recombinants, and iii) their derived 369 F2:3 progenies, from a cross involving introgression lines RSG04008-6 (susceptible) × J2614-11 (resistant). The QTLs were mapped to a 37–72 centimorgan (cM) or 5–15 Mb interval on the long arm of sorghum chromosome 10 (SBI-10L) with flanking markers Xgap001 and Xtxp141. One QTL each for glossiness (QGls10) and trichome density (QTd10) were mapped in marker interval Xgap001-Xnhsbm1044 and Xisep0630-Xtxp141, confirming their loose linkage, for which phenotypic variation accounted for ranged from 2.29 to 11.37 % and LOD values ranged from 2.03 to 24.13, respectively. Average physical map positions for glossiness and trichome density QTLs on SBI-10 from earlier studies were 4 and 2 Mb, which in the present study were reduced to 2 Mb and 800 kb, respectively. Candidate genes Glossy15 (Sb10g025053) and ethylene zinc finger protein (Sb10g027550) falling in support intervals for glossiness and trichome density QTLs, respectively, are discussed. Also we identified a sub-set of recombinant population that will facilitate further fine mapping of the leaf blade glossiness and trichome density QTLs on SBI-10.AbstractShoot fly is a major insect pest of sorghum damaging early crop growth, establishment and productivity. Host plant resistance is an efficient approach to minimize yield losses due to shoot fly infestation. Seedling leaf blade glossiness and trichome density are morphological traits associated with shoot fly resistance. Our objective was to identify and evaluate QTLs for glossiness and trichome density using- i) 1894 F2s, ii) a sub-set of 369 F2-recombinants, and iii) their derived 369 F2:3 progenies, from a cross involving introgression lines RSG04008-6 (susceptible) × J2614-11 (resistant). The QTLs were mapped to a 37–72 centimorgan (cM) or 5–15 Mb interval on the long arm of sorghum chromosome 10 (SBI-10L) with flanking markers Xgap001 and Xtxp141. One QTL each for glossiness (QGls10) and trichome density (QTd10) were mapped in marker interval Xgap001-Xnhsbm1044 and Xisep0630-Xtxp141, confirming their loose linkage, for which phenotypic variation accounted for ranged from 2.29 to 11.37 % and LOD values ranged from 2.03 to 24.13, respectively. Average physical map positions for glossiness and trichome density QTLs on SBI-10 from earlier studies were 4 and 2 Mb, which in the present study were reduced to 2 Mb and 800 kb, respectively. Candidate genes Glossy15 (Sb10g025053) and ethylene zinc finger protein (Sb10g027550) falling in support intervals for glossiness and trichome density QTLs, respectively, are discussed. Also we identified a sub-set of recombinant population that will facilitate further fine mapping of the leaf blade glossiness and trichome density QTLs on SBI-10.222:3Xgap001Xtxp141QGls10QTd10Xgap001Xnhsbm1044Xisep0630Xtxp141Glossy15

Pub.: 16 Dec '15, Pinned: 05 Jan '18

Introgression of Shoot Fly (Atherigona soccata L. Moench) Resistance QTLs into Elite Post-rainy Season Sorghum Varieties Using Marker Assisted Backcrossing (MABC).

Abstract: Shoot fly (Atherigona soccata L. Moench) is a serious pest in sorghum production. Management of shoot fly using insecticides is expensive and environmentally un-safe. Developing host-plant resistance is the best method to manage shoot fly infestation. Number of component traits contribute for imparting shoot fly resistance in sorghum and molecular markers have been reported which were closely linked to QTLs controlling these component traits. In this study, three QTLs associated with shoot fly resistance were introgressed into elite cultivars Parbhani Moti (= SPV1411) and ICSB29004 using marker assisted backcrossing (MABC). Crosses were made between recurrent parents and the QTL donors viz., J2658, J2614, and J2714. The F1s after confirmation for QTL presence were backcrossed to recurrent parents and the resultant lines after two backcrosses were selfed thrice for advancement. The foreground selection was carried out in F1 and BCnF1 generations with 22 polymorphic markers. Forty-three evenly distributed simple sequence repeat markers in the sorghum genome were used in background selection to identify plants with higher recurrent parent genome recovery. By using two backcrosses and four rounds of selfing, six BC2F4 progenies were selected for ICSB29004 × J2658, five BC2F4 progenies were selected for ICSB29004 × J2714 and six BC2F4 progenies were selected for Parbhani Moti × J2614 crosses. Phenotyping of these lines led to the identification of two resistant lines for each QTL region present on chromosome SBI-01, SBI-07 and SBI-10 in ICSB 29004 and Parbhani Moti. All the introgression lines (ILs) showed better shoot fly resistance than the recurrent parents and their agronomic performance was the same or better than the recurrent parents. Further, the ILs had medium plant height, desirable maturity with high yield potential which makes them better candidates for commercialization. In the present study, MABC has successfully improved the shoot fly resistance in sorghum without a yield penalty. This is the first report on the use of MABC for improving shoot fly resistance in post-rainy season sorghum.

Pub.: 19 Sep '17, Pinned: 05 Jan '18

Stay-green expression in early generation sorghum [Sorghum bicolor (L.) Moench] QTL introgression lines

Abstract: Reduced leaf senescence (stay-green) has been demonstrated to improve tolerance of post-flowering moisture stress in grain sorghum. A number of quantitative trait loci (QTLs) associated with stay-green have been identified in sorghum, to facilitate transfer of this trait into adapted genetic backgrounds. This study reports initial evaluations, in both well watered and post-flowering stress environments, following partial introgression (BC2F3/BC1F4 generations) of four stable stay-green QTLs (StgB, Stg1, Stg3 and Stg4) from donor parent B35 to senescent variety R 16. The majority of the introgression lines had higher leaf chlorophyll levels at flowering (a distinctive trait of the donor parent) and a greater percentage green leaf area during the latter part of grain filling, than did R 16, indicating that the stay-green QTLs were expressed phenotypically in the R 16 background. None of the QTL introgression lines achieved the same level of stay-green as B35, however. Maintenance of a greater relative green leaf area during the latter half of grain filling was related to a greater relative grain yield in two of three post-flowering moisture deficit environments in which the materials were evaluated (r2 = 0.34 in 2004–2005 and r2 = 0.76 in 2005–2006), as was a direct measure of leaf chlorophyll in one of the post-flowering stress environments in which this was measured (r2 = 0.42, P < 0.05). Thus the study provided useful evidence that the marker-assisted backcross transfer of stay-green QTLs from B35 into an adapted, but senescent background has the potential to enhance tolerance of post-flowering drought stress in sorghum.

Pub.: 25 Dec '09, Pinned: 05 Jan '18

Detection and validation of stay-green QTL in post-rainy sorghum involving widely adapted cultivar, M35-1 and a popular stay-green genotype B35.

Abstract: Sorghum [Sorghum bicolor (L.) Moench] is an important dry-land cereal of the world providing food, fodder, feed and fuel. Stay-green (delayed-leaf senescence) is a key attribute in sorghum determining its adaptation to terminal drought stress. The objective of this study was to validate sorghum stay-green quantitative trait loci (QTL) identified in the past, and to identify new QTL in the genetic background of a post-rainy adapted genotype M35-1.A genetic linkage map based on 245 F9 Recombinant Inbred Lines (RILs) derived from a cross between M35-1 (more senescent) and B35 (less senescent) with 237 markers consisting of 174 genomic, 60 genic and 3 morphological markers was used. The phenotypic data collected for three consecutive post-rainy crop seasons on the RIL population (M35-1 × B35) was used for QTL analysis. Sixty-one QTL were identified for various measures of stay-green trait and each trait was controlled by one to ten QTL. The phenotypic variation explained by each QTL ranged from 3.8 to 18.7%. Co-localization of QTL for more than five traits was observed on two linkage groups i.e. on SBI-09-3 flanked by S18 and Xgap206 markers and, on SBI-03 flanked by XnhsbSFCILP67 and Xtxp31. QTL identified in this study were stable across environments and corresponded to sorghum stay-green and grain yield QTL reported previously. Of the 60 genic SSRs mapped, 14 were closely linked with QTL for ten traits. A genic marker, XnhsbSFCILP67 (Sb03g028240) encoding Indole-3-acetic acid-amido synthetase GH3.5, was co-located with QTL for GLB, GLM, PGLM and GLAM on SBI-03. Genes underlying key enzymes of chlorophyll metabolism were also found in the stay-green QTL regions.We validated important stay-green QTL reported in the past in sorghum and detected new QTL influencing the stay-green related traits consistently. Stg2, Stg3 and StgB were prominent in their expression. Collectively, the QTL/markers identified are likely candidates for subsequent verification for their involvement in stay-green phenotype using NILs and to develop drought tolerant sorghum varieties through marker-assisted breeding for terminal drought tolerance in sorghum.

Pub.: 19 Oct '14, Pinned: 05 Jan '18

Stay-green traits to improve wheat adaptation in well-watered and water-limited environments

Abstract: A stay-green phenotype enables crops to retain green leaves longer after anthesis compared with senescent types, potentially improving yield. Measuring the normalized difference vegetative index (NDVI) during the whole senescence period allows quantification of component stay-green traits contributing to a stay-green phenotype. These objective and standardized traits can be compared across genotypes and environments. Traits examined include maximum NDVI near anthesis (Nmax), senescence rate (SR), a trait integrating senescence (SGint), plus time from anthesis to onset (OnS), mid-point (MidS), and near completion (EndS) of senescence. The correlation between stay-green traits and yield was studied in eight contrasting environments ranging from well watered to severely water limited. Environments were each classified into one of the four major drought environment types (ETs) previously identified for the Australian wheat cropping system. SGint, OnS, and MidS tended to have higher values in higher yielding environments for a given genotype, as well as for higher yielding genotypes within a given environment. Correlation between specific stay-green traits and yield varied with ET. In the studied population, SGint, OnS, and MidS strongly correlated with yield in three of the four ETs which included well-watered environments (0.43–0.86), but less so in environments with only moderate water-stress after anthesis (–0.03 to 0.31). In contrast, Nmax was most highly correlated with yield under moderate post-anthesis water stress (0.31–0.43). Selection for particular stay-green traits, combinations of traits, and/or molecular markers associated with the traits could enhance genetic progress toward stay-green wheats with higher, more stable yield in both well-watered and water-limited conditions.

Pub.: 07 Sep '16, Pinned: 05 Jan '18

Defect in non-yellow coloring 3, an alpha/beta hydrolase-fold family protein, causes a stay-green phenotype during leaf senescence in rice.

Abstract: Chlorophyll degradation is an important phenomenon in the senescence process. It is necessary for the degradation of certain chlorophyll-protein complexes and thylakoid membranes during leaf senescence. Mutants retaining greenness during leaf senescence are known as 'stay-green' mutants. Non-functional type stay-green mutants, which possess defects in chlorophyll degradation, retain greenness but not leaf functionality during senescence. Here, we report a new stay-green mutant in rice, nyc3. nyc3 retained a higher chlorophyll a and chlorophyll b content than the wild-type but showed a decrease in other senescence parameters during dark incubation, suggesting that it is a non-functional stay-green mutant. In addition, a small amount of pheophytin a, a chlorophyll a-derivative without Mg(2+) ions in its tetrapyrrole ring, accumulated in the senescent leaves of nyc3. nyc3 shows a similar but weaker phenotype to stay green (sgr), another non-functional stay-green mutant in rice. The chlorophyll content of nyc3 sgr double mutants at the late stage of leaf senescence was also similar to that of sgr. Linkage analysis revealed that NYC3 is located near the centromere region of chromosome 6. Map-based cloning of genes near the centromere is very difficult because of the low recombination rate; however, we overcame this problem by using ionizing radiation-induced mutant alleles harboring deletions of hundreds of kilobases. Thus, it was revealed that NYC3 encodes a plastid-localizing alpha/beta hydrolase-fold family protein with an esterase/lipase motif. The possible function of NYC3 in the regulation of chlorophyll degradation is discussed.

Pub.: 21 May '09, Pinned: 05 Jan '18

The senescence-induced staygreen protein regulates chlorophyll degradation.

Abstract: Loss of green color in leaves results from chlorophyll (Chl) degradation in chloroplasts, but little is known about how Chl catabolism is regulated throughout leaf development. Using the staygreen (sgr) mutant in rice (Oryza sativa), which maintains greenness during leaf senescence, we identified Sgr, a senescence-associated gene encoding a novel chloroplast protein. Transgenic rice overexpressing Sgr produces yellowish-brown leaves, and Arabidopsis thaliana pheophorbide a oxygenase-impaired mutants exhibiting a stay-green phenotype during dark-induced senescence have reduced expression of Sgr homologs, indicating that Sgr regulates Chl degradation at the transcriptional level. We show that the leaf stay-greenness of the sgr mutant is associated with a failure in the destabilization of the light-harvesting chlorophyll binding protein (LHCP) complexes of the thylakoid membranes, which is a prerequisite event for the degradation of Chls and LHCPs during senescence. Transient overexpression of Sgr in Nicotiana benthamiana and an in vivo pull-down assay show that Sgr interacts with LHCPII, indicating that the Sgr-LHCPII complexes are formed in the thylakoid membranes. Thus, we propose that in senescing leaves, Sgr regulates Chl degradation by inducing LHCPII disassembly through direct interaction, leading to the degradation of Chls and Chl-free LHCPII by catabolic enzymes and proteases, respectively.

Pub.: 22 May '07, Pinned: 05 Jan '18

Molecular cloning and function analysis of the stay green gene in rice.

Abstract: Chloroplasts undergo drastic morphological and physiological changes during senescence with a visible symptom of chlorophyll (Chl) degradation. A stay green mutant was identified and then isolated from the japonica rice (Oryza sativa) cv. Huazhiwu by gamma-ray irradiation. The stay green mutant was characterized by Chl retention, stable Chl-protein complexes, and stable thylakoid membrane structures, but lost its photosynthetic competence during senescence. The gene, designated Stay Green Rice (SGR), was cloned by a positional cloning strategy encoding an ancient protein containing a putative chloroplast transit peptide. SGR protein was found in both soluble and thylakoid membranes in rice. SGR, like the gene for pheophorbide a oxygenase (PaO), was constitutively expressed, but was upregulated by dark-induced senescence in rice leaves. Senescence-induced expression of SGR and PaO was enhanced by ABA, but inhibited by cytokinin. Overexpression of SGR reduced the number of lamellae in the grana thylakoids and reduced the Chl content of normally growing leaves. This indicates that upregulation of SGR increases Chl breakdown during senescence in rice. A small quantity of chlorophyllide a accumulated in sgr leaves, but this also accumulated in wild-type rice leaves during senescence. Some pheophorbide a was detected in sgr leaves in the dark. According to these observations, we propose that SGR may be involved in regulating or taking part in the activity of PaO, and then may influence Chl breakdown and degradation of pigment-protein complex.

Pub.: 24 Aug '07, Pinned: 05 Jan '18

Differential effect of whole-ear shading after heading on the physiology, biochemistry and yield index of stay-green and non-stay-green wheat genotypes.

Abstract: Two winter wheat cultivars (the functional stay-green CN12 and non-stay-green CN19) were used to investigate the effects of ear-shading on grain yield and to elucidate the differential mechanisms of different cultivars. The photosynthetic parameters, chlorophyll fluorescence, antioxidant enzyme activities, and chlorophyll contents were measured 0, 15 and 30 days after heading (DAH) under both shaded and non-shaded conditions. The final grain-yield index was also measured. Shading had a smaller effect on the net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), maximal photochemical efficiency of PSII (Fv/Fm) and coefficient of non-photochemical fluorescence quenching (qN) but a greater effect on both superoxide dismutase (SOD) and catalase (CAT) activities in CN12 than it did in CN19. Shading slightly altered the timeframe of leaf senescence in CN12 and may have accelerated leaf senescence in CN19. Moreover, shading had only a small effect on the weight of grains per spike (WGS) in CN12 compared with CN19, mainly resulting from the number of grains per spike (NGS) rather than the 1000-grain weight (SGW). In conclusion, the flag leaves of functional stay-green wheat could serve as potential "buffers" and/or "compensators" for ear photosynthesis, which is actively regulated by the antioxidant enzyme system and prevents yield loss. Thus, a functional stay-green genotype could be more tolerant to environmental stress than a non-stay-green genotype.

Pub.: 06 Feb '17, Pinned: 05 Jan '18

Sorghum stay-green QTL individually reduce post-flowering drought-induced leaf senescence.

Abstract: Sorghum is an important source of food, feed, and biofuel, especially in the semi-arid tropics because this cereal is well adapted to harsh, drought-prone environments. Post-flowering drought adaptation in sorghum is associated with the stay-green phenotype. Alleles that contribute to this complex trait have been mapped to four major QTL, Stg1-Stg4, using a population derived from BTx642 and RTx7000. Near-isogenic RTx7000 lines containing BTx642 DNA spanning one or more of the four stay-green QTL were constructed. The size and location of BTx642 DNA regions in each RTx7000 NIL were analysed using 62 DNA markers spanning the four stay-green QTL. RTx7000 NILs were identified that contained BTx642 DNA completely or partially spanning Stg1, Stg2, Stg3, or Stg4. NILs were also identified that contained sub-portions of each QTL and various combinations of the four major stay-green QTL. Physiological analysis of four RTx7000 NILs containing only Stg1, Stg2, Stg3, or Stg4 showed that BTx642 alleles in each of these loci could contribute to the stay-green phenotype. RTx7000 NILs containing BTx642 DNA corresponding to Stg2 retained more green leaf area at maturity under terminal drought conditions than RTx7000 or the other RTx7000 NILs. Under post-anthesis water deficit, a trend for delayed onset of leaf senescence compared with RTx7000 was also exhibited by the Stg2, Stg3, and Stg4 NILs, while significantly lower rates of leaf senescence in relation to RTx7000 were displayed by all of the Stg NILs to varying degrees, but particularly by the Stg2 NIL. Greener leaves at anthesis relative to RTx7000, indicated by higher SPAD values, were exhibited by the Stg1 and Stg4 NILs. The RTx7000 NILs created in this study provide the starting point for in-depth analysis of stay-green physiology, interaction among stay-green QTL and map-based cloning of the genes that underlie this trait.

Pub.: 19 Dec '06, Pinned: 05 Jan '18

The stay-green trait.

Abstract: Stay-green (sometimes staygreen) refers to the heritable delayed foliar senescence character in model and crop plant species. In a cosmetic stay-green, a lesion interferes with an early step in chlorophyll catabolism. The possible contribution of synthesis to chlorophyll turnover in cosmetic stay-greens is considered. In functional stay-greens, the transition from the carbon capture period to the nitrogen mobilization (senescence) phase of canopy development is delayed, and/or the senescence syndrome proceeds slowly. Yield and composition in high-carbon (C) crops such as cereals, and in high-nitrogen (N) species such as legumes, reflect the source-sink relationship with canopy C capture and N remobilization. Quantitative trait loci studies show that functional stay-green is a valuable trait for improving crop stress tolerance, and is associated with the domestication syndrome in cereals. Stay-green variants reveal how autumnal senescence and dormancy are coordinated in trees. The stay-green phenotype can be the result of alterations in hormone metabolism and signalling, particularly affecting networks involving cytokinins and ethylene. Members of the WRKY and NAC families, and an ever-expanding cast of additional senescence-associated transcription factors, are identifiable by mutations that result in stay-green. Empirical selection for functional stay-green has contributed to increasing crop yields, particularly where it is part of a strategy that also targets other traits such as sink capacity and environmental sensitivity and is associated with appropriate crop management methodology. The onset and progress of senescence are phenological metrics that show climate change sensitivity, indicating that understanding stay-green can contribute to the design of appropriate crop types for future environments.

Pub.: 07 Mar '14, Pinned: 05 Jan '18

Responses to N Deficiency in Stay Green and Non‐Stay Green Argentinean Hybrids of Maize

Abstract: Breeding has developed better yielding maize hybrids for low N environments, which also have delayed leaf senescence (‘stay green’ trait, SG). Here, we studied whether the SG trait can further improve yield of modern hybrids under N‐limiting conditions. In two field experiments, four maize hybrids with different senescence behaviour were grown under three N fertilization levels, from 0 to 200 kg N ha−1 (N0, N100 and N200). After silking, hybrids differed for senescence depending on the canopy layer (P < 0.05): the SG AX878 only delayed senescence at the mid and upper canopy layers while the SG NK880 delayed senescence of all layers. Across N doses, higher yields were achieved by both SG hybrids, AX878 and NK880 (P < 0.05) but yield was not only determined by senescence behaviour. Kernel weight (KW) response to N availability was larger for SGs than for their non‐‘stay green’ counterparts. Delayed senescence in SG hybrids was not related to higher post‐silking N uptake but to higher (P < 0.05) %N in leaves and lower (P < 0.05) %N in kernels at harvest (below the critical 1.1 % under N deficiency). Across N levels, KW positively related to N content per kernel, with a steeper slope (P < 0.05) for the SG hybrids. Taken together, our results suggest that a condition where N limits kernel growth, in a scenario of saturating C availability, may be common to stay green genotypes of maize.

Pub.: 22 Jun '15, Pinned: 05 Jan '18

Characterization of photosynthetic performance during senescence in stay-green and quick-leaf-senescence Zea mays L. inbred lines.

Abstract: The net photosynthetic rate, chlorophyll content, chlorophyll fluorescence and 820 nm transmission were investigated to explore the behavior of the photosynthetic apparatus, including light absorption, energy transformation and the photoactivities of photosystem II (PSII) and photosystem I (PSI) during senescence in the stay-green inbred line of maize (Zea mays) Q319 and the quick-leaf-senescence inbred line of maize HZ4. The relationship between the photosynthetic performance and the decrease in chlorophyll content in the two inbred lines was also studied. Both the field and laboratory data indicated that the chlorophyll content, net photosynthetic rate, and the photoactivities of PSII and PSI decreased later and slower in Q319 than in HZ4, indicating that Q319 is a functional stay-green inbred line. In order to avoid the influence of different development stages and environmental factors on senescence, age-matched detached leaf segments from the two inbred lines were treated with ethephon under controlled conditions to induce senescence. The net photosynthetic rate, light absorption, energy transformation, the activities of PSII acceptor side and donor side and the PSI activities decreased much slower in Q319 than in HZ4 during the ethephon-induced senescence. These results suggest that the retention of light absorption, energy transformation and activity of electron transfer contribute to the extended duration of active photosynthesis in Q319. Although the chlorophyll content decreased faster in HZ4, with decrease of chlorophyll content induced by ethephon, photosynthetic performance of Q319 deteriorated much more severely than that of HZ4, indicating that, compared with Q319, HZ4 has an advantage at maintaining higher photosynthetic activity with decrease of chlorophyll although HZ4 is a quick-leaf-senescence inbred line. We conclude that attention should be paid to two favorable characteristics in breeding long duration of active photosynthesis hybrids: 1) maintaining more chlorophyll content during senescence and 2) maintaining higher photosynthetic activity during the loss of chlorophyll.

Pub.: 18 Aug '12, Pinned: 05 Jan '18

Identification and fine mapping of a stay-green gene (Brnye1) in pakchoi (Brassica campestris L. ssp. chinensis)

Abstract: Using bulked segregant analysis combined with next-generation sequencing, we delimited theBrnye1gene responsible for the stay-green trait ofnyein pakchoi. Sequence analysis identifiedBra019346as the candidate gene.“Stay-green” refers to a plant trait whereby leaves remain green during senescence. This trait is useful in the cultivation of pakchoi (Brassica campestris L. ssp. chinensis), which is marketed as a green leaf product. This study aimed to identify the gene responsible for the stay-green trait in pakchoi. We identified a stay-green mutant in pakchoi, which we termed “nye”. Genetic analysis revealed that the stay-green trait is controlled by a single recessive gene, Brnye1. Using the BSA-seq method, a 3.0-Mb candidate region was mapped on chromosome A03, which helped us localize Brnye1 to an 81.01-kb interval between SSR markers SSRWN27 and SSRWN30 via linkage analysis in an F2 population. We identified 12 genes in this region, 11 of which were annotated based on the Brassica rapa annotation database, and one was a functionally unknown gene. An orthologous gene of the Arabidopsis gene AtNYE1, Bra019346, was identified as the potential candidate for Brnye1. Sequence analysis revealed a 40-bp insertion in the second exon of Bra019346 in nye, which generated the TAA stop codon. A candidate gene-specific Indel marker in 1561 F2 individuals showed perfect cosegregation with Brnye1 in the nye mutant. These results provide a foundation for uncovering the molecular mechanism of the stay-green trait in pakchoi.

Pub.: 05 Dec '17, Pinned: 05 Jan '18

Histone MacroH2A1: A Chromatin Point of Intersection between Fasting, Senescence and Cellular Regeneration.

Abstract: Histone variants confer chromatin unique properties. They have specific genomic distribution, regulated by specific deposition and removal machineries. Histone variants, mostly of canonical histones H2A, H2B and H3, have important roles in early embryonic development, in lineage commitment of stem cells, in the converse process of somatic cell reprogramming to pluripotency and, in some cases, in the modulation of animal aging and life span. MacroH2A1 is a variant of histone H2A, present in two alternatively exon-spliced isoforms macroH2A1.1 and macroH2A1.2, regulating cell plasticity and proliferation, during pluripotency and tumorigenesis. Furthermore, macroH2A1 participates in the formation of senescence-associated heterochromatic foci (SAHF) in senescent cells, and multiple lines of evidence in genetically modified mice suggest that macroH2A1 integrates nutritional cues from the extracellular environment to transcriptional programs. Here, we review current molecular evidence based on next generation sequencing data, cell assays and in vivo models supporting different mechanisms that could mediate the function of macroH2A1 in health span and life span. We will further discuss context-dependent and isoform-specific functions. The aim of this review is to provide guidance to assess histone variant macroH2A1 potential as a therapeutic intervention point.

Pub.: 06 Dec '17, Pinned: 05 Jan '18

Quantitative proteomics analysis of proteins involved in leaf senescence of rice ( Oryza sativa L.)

Abstract: Delaying leaf senescence and prolonging the available time for photosynthesis is one of the important approaches to increase grain yield of rice (Oryza sativa L.). Here, iTRAQ-based quantitative proteomics approach was used to comparative analyze the expression profiles of proteins in rice leaves in response to senescence. Totally 5067 proteins were identified. Compared with the proteins in the flag leaves at early stage of grain-filling in rice Liang-You-Pei 9 (LYP9), 240 and 188 proteins were up-regulated and down-regulated in the flag leaves at middle stage of grain-filling, and 387 and 202 proteins were up-regulated and down-regulated in the flag leaves at late stage of grain-filling, respectively. In addition, 39 and 18 identified proteins were constantly up-regulated and down-regulated in the leaves from early to middle and late stages of grain-filling, respectively. Among them, chloroplast chaperonin 10, geranylgeranyl diphosphate reductase, Mg chelatase subunit ChLD, porphobilinogen deaminase, protochlorophyllide reductase B and thioredoxin-like protein CITRX might have involved in the senescence of leaves. This study provided important information for understanding the age-sensitive mechanism of LYP9, and offered a foundation for future studying and improving it. Delaying leaf senescence and prolonging the available time for photosynthesis is one of the important approaches to increase grain yield of rice (Oryza sativa L.). Here, iTRAQ-based quantitative proteomics approach was used to comparative analyze the expression profiles of proteins in rice leaves in response to senescence. Totally 5067 proteins were identified. Compared with the proteins in the flag leaves at ea

Pub.: 27 Nov '17, Pinned: 05 Jan '18

Evolutionary history of the NAM-B1 gene in wild and domesticated tetraploid wheat

Abstract: The NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size. First detected in wild emmer wheat, the wild-type allele of the gene has been introgressed into durum and bread wheat. Later studies have, however, also found the presence of the wild-type allele in some domesticated subspecies. In this study we trace the evolutionary history of the NAM-B1 in tetraploid wheat species and evaluate it as a putative domestication gene.Genotyping of wild and landrace tetraploid accessions showed presence of only null alleles in durum. Domesticated emmer wheats contained both null alleles and the wild-type allele while wild emmers, with one exception, only carried the wild-type allele. One of the null alleles consists of a deletion that covers several 100 kb. The other null-allele, a one-basepair frame-shift insertion, likely arose among wild emmer. This allele was the target of a selective sweep, extending over several 100 kb.The NAM-B1 gene fulfils some criteria for being a domestication gene by encoding a trait of domestication relevance (seed size) and is here shown to have been under positive selection. The presence of both wild-type and null alleles in domesticated emmer does, however, suggest the gene to be a diversification gene in this species. Further studies of genotype-environment interactions are needed to find out under what conditions selection on different NAM-B1 alleles have been beneficial.

Pub.: 20 Dec '17, Pinned: 05 Jan '18