Regulation of flowering time in Arabidopsis



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Flowering pathway

Gibberellin pathway



The Gibberellin transduction pathway


RGL1 and RGL2 (RGA-LIKE 1 and 2)


The cloning of the RGL genes was reported by Sanchez-Fernandez et al. (1998) and Dill and Sun (2001).

RGL1 and RGL2 have strong sequence similarities with RGA and GAI. They all belong to the GRAS family of transcriptional regulators and contain two conserved regions:  the VHIID region and the DELLA region (DELLV in the case of RGL1) (Mouradov et al., 2002; Lee et al., 2002; Wen and Chang, 2002).

RGL1 and RGL2 expression is high in the seeds, but low in vegetative tissues. In the adult plants, RGL1 is expressed mainly in the inflorescence, whereas RGL2 is expressed in the inflorescence and in the siliques (Wen and Chang, 2002; Lee et al., 2002; Tyler et al., 2004).

RGL2 is mainly a repressor of germination. RGL1 plays a role in stem elongation and leaf expansion, as well as in flower development. The role of these two genes in the regulation of flowering time is much more limited, and mostly masked by the effects of RGA and GAI (Wen and Chang, 2002; Tyler et al., 2004; Cheng et al., 2004).

rgl1-2, rgl2-13 and rgl3-3 are T-DNA insertion mutant alleles. As the insertion is located in the middle of the coding sequence, they are loss-of-function alleles (Tyler et al., 2004). In the WT background, the rgl1-2 and rgl2-13  mutants have a WT phenotype (Tyler et al., 2004).

RGL1 and RGL2 are negative regulators of flowering time:

In the ga1-3 background, the loss of RGA and GAI accelerates flowering, and the loss of RGL1 and RGL2 further accelerates flowering (by one or 2 leaves), both in short days and in long days (the effect is more marked in short days). However, if either RGA or GAI are functional in the ga1-3 background, the loss of RGL1 or RGL2 function has no visible effect (Cheng et al., 2004).

However, these observations were made on the La-er ecotype (Cheng et al., 2004). In the Col ecotype, no clear effect of RGL1 or RGL2 on flowering time could be observed (Tyler et al., 2004).

RGL1 is not GA-regulated:

Unlike RGA, and like GAI, the RGL1 protein is not degraded upon GA treatment (Wen and Chang, 2002).

Interaction between GAs, SLY1 and RGLs.

Redundancy between DELLA protein genes.