Floral homeotic genes are targets of gibberellin signaling in flower development

Abstract

Gibberellins (GAs) are a class of plant hormones involved in the regulation of flower development in Arabidopsis . The GA-deficient ga1 - 3 mutant shows retarded growth of all floral organs, especially abortive stamen development that results in complete male sterility. Until now, it has not been clear how GA regulates the late-stage development of floral organs after the establishment of their identities within floral meristems. Various combinations of null mutations of DELLA proteins can gradually rescue floral defects in ga1 - 3 . In particular, the synergistic effect of rga - t2 and rgl2 - 1 can substantially restore flower development in ga1 - 3 . We find that the transcript levels of floral homeotic genes APETALA3 ( AP3 ), PISTILLATA ( PI ), and AGAMOUS ( AG ) are immediately upregulated in young flowers of ga1 - 3 upon GA treatment. Using a steroid-inducible activation of RGA, we further demonstrated that these floral homeotic genes are transcriptionally repressed by RGA activity in young flowers whereas the expression of LEAFY ( LFY ) and APETALA1 ( AP1 ) is not substantially affected. In addition, we observed the partial rescue of floral defects in ga1 - 3 by overexpression of AG . Our results indicate that GA promotes the expression of floral homeotic genes by antagonizing the effects of DELLA proteins, thereby allowing continued flower development.