A pinboard by
A S M Mainul Hasan

PhD student investigating flowering time mechanism in garden pea.


Decorative flower or edible food production - how is the latent genetic machinery driven in plants?

Have you ever thought of what is the genetic mechanism that mediates and ultimately gives rise to the beautiful flowers that you buy as a gift for your loved ones? It would probably be very fascinating for you as well to get an insight into the molecular process of fruit/vegetable/grain production being consumed by us everyday, which commences through initiation of flowering in a particular plant. Let’s get some very basic knowledge on this biological phenomenon that we observe in nature and is directly related to our survival.

The onset of flowering is a key developmental transition in the plant life cycle and is regulated by different environmental factors such as photoperiod, temperature and endogenous cues like circadian clock, gibberellic acid and age of the plant. Arabidopsis thaliana/Thale cress has been extensively used as a model system by researchers for unveiling the molecular biology of flowering which encompasses several reasons: its small genome size, easy handling, short life cycle, comparatively fast generation time and prolific seed production.

A. thaliana is a facultative long day plant where flowering is regulated by a key mobile protein, FLOWERING LOCUS T (FT) that is known as florigen. FT expression is dependent on CONSTANS (CO) in leaves under long day (LD) where different other genes play positive and negative roles in regulating FT function. FT is transported from leaves to shoot apical meristem (SAM) where it interacts with a basic leucine zipper (bZIP) domain transcription factor, FD. In the SAM, the FT–FD complex induces expression of floral meristem identity genes such as LEAFY (LFY) and APETALA1 (AP1) via SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and this leads to commencement of flower formation. During winter, a MADS-box DNA binding protein FLOWERING LOCUS C (FLC) plays the central role in suppressing the expression of FT. Exposure to low temperatures (vernalization) induces expression of genes that repress FLC expression during warm temperature of the following spring, relieving the repression of FLC on FT and allowing the plant to initiate flowering process through FT action.

While flowering mechanisms are well understood in A. thaliana, they are less well perceived in other higher plant groups such as ornamental plants and crops. Therefore, scientists use knowledge gained from A. thaliana as a fundamental basis to investigate the genetic mechanism that regulates flowering time in higher plant species.


Long-distance, graft-transmissible action of Arabidopsis FLOWERING LOCUS T protein to promote flowering.

Abstract: Day length perceived by a leaf is a major environmental factor that controls the timing of flowering. It has been believed that a mobile, long-distance signal called florigen is produced in the leaf under inductive day length conditions, and is transported to the shoot apex where it triggers floral morphogenesis. Grafting experiments have shown that florigen is transmissible from a donor plant that has been subjected to inductive day length to an uninduced recipient plant. However, the nature of florigen has long remained elusive. Arabidopsis FLOWERING LOCUS T (FT) is expressed in cotyledons and leaves in response to inductive long days (LDs). FT protein, with a basic region/leucine zipper (bZIP) transcription factor FD, acts in the shoot apex to induce target meristem identity genes such as APETALA1 (AP1) and initiates floral morphogenesis. Recent studies have provided evidence that the FT protein in Arabidopsis and corresponding proteins in other species are an important part of florigen. Our work shows that the FT activity, either from overexpressing or inducible transgenes or from the endogenous gene, to promote flowering is transmissible through a graft junction, and that an FT protein with a T7 tag is transported from a donor scion to the apical region of recipient stock plants and becomes detectable within a day or two. The sequence and structure of mRNA are not of critical importance for the long-distance action of the FT gene. These observations led to the conclusion that the FT protein, but not mRNA, is the essential component of florigen.

Pub.: 14 Oct '08, Pinned: 20 Apr '17