Indexed on: 31 Dec '20Published on: 29 Sep '19Published in: Journal of experimental botany
LAZY 1 family genes play important roles in both shoot and root gravitropism in plants. Here we report a Lotus japonicus mutant that displays negative gravitropic response in primary and lateral roots. Map-based cloning identified the mutant gene LjLAZY3 as a functional ortholog of the LAZY1 gene. The mutation of the LjLAZY3 gene reduced rootward polar auxin transport (PAT) in the primary root, which was also insensitive to the PAT inhibitor N-1-naphthylphthalamic acid. Moreover, immunolocalization of eGFP-tagged LjLAZY3 in L. japonicus exhibited the polar localization of LjLAZY3 on the plasma membrane in root stele cells. We therefore suggest that the polar localization of LjLAZY3 in stele cells might be required for PAT in L. japonicus root. LjLAZY3 transcripts displayed asymmetric distribution at the root tip within hours of gravistimulation, while overexpression of LjLAZY3 under a constitutive promoter in Ljlazy3 rescued the gravitropic response in roots. These data indicate that root gravitropism depends on the presence of LjLAZY3 but not its asymmetric expression in root tips. Expression of other LAZY genes in Ljlazy3 background did not rescue the growth direction of roots, suggesting that the LjLAZY3 gene plays a distinct role in root gravitropism in L.japonicus. © The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.