Gibberellin regulatesArabidopsisfloral development via suppression of DELLA protein function

Abstract

The phytohormone gibberellin (GA) regulates the development and fertility of Arabidopsis flowers. The mature flowers of GA-deficient mutant plants typically exhibit reduced elongation growth of petals and stamens. In addition, GA-deficiency blocks anther development, resulting in male sterility. Previous analyses have shown that GA promotes the elongation of plant organs by opposing the function of the DELLA proteins, a family of nuclear growth repressors. However, it was not clear that the DELLA proteins are involved in the GA-regulation of stamen and anther development. We show that GA regulates cell elongation rather than cell division during Arabidopsis stamen filament elongation. In addition, GA regulates the cellular developmental pathway of anthers leading from microspore to mature pollen grain. Genetic analysis shows that the Arabidopsis DELLA proteins RGA and RGL2 jointly repress petal, stamen and anther development in GA-deficient plants, and that this function is enhanced by RGL1 activity. GA thus promotes Arabidopsis petal, stamen and anther development by opposing the function of the DELLA proteins RGA, RGL1 and RGL2.

Genetic Characterization and Functional Analysis of the GID1 Gibberellin Receptors inArabidopsis

“…However, based on the lack of any obvious phenotypic defects in the gid1b-1 mutant, the physiological significance of this increased affinity is not evident. It is known that the five DELLAs exhibit both overlapping and distinct roles in regulating GA-responsive growth in Arabidopsis King et al, 2001;Lee et al, 2002;Cheng et al, 2004;Tyler et al, 2004). It is conceivable that individual Arabidopsis GID1s display specificity for the DELLAs they target, although our data and those of Nakajima et al (2006) do not support this model; there are no clear differences in binding specificity of individual Arabidopsis GID1s to the different DELLAs in yeast two-hybrid assays.…”

“…The floral organ defects observed in the triple mutant include a dramatic reduction in the length of the pistil, although elongation of the papillae appears to be unaffected, and arrest of the stamens at an earlier stage of development than in ga1-3 ( Figures 2E and 2F). Petal and stamen development do not progress beyond floral stage 10 in ga1-3 (Cheng et al, 2004). While the petal development in the gid1a-1 gid1b-1 gid1c-1 mutant appears similar to that in ga1-3, the stamens appear to be arrested earlier, before stage 9, based on the lack of differentiation between the filament and the anthers (Smyth et al, 1990).…”

“…In Arabidopsis, they promote floral initiation and the development of floral organs, seeds, and siliques (Wilson et al, 1992;Singh et al, 2002;Cheng et al, 2004). To assess the involvement of the Arabidopsis GID1 genes in these developmental processes, we have characterized reproductive development in all combinations of mutants.…”

“…In the Arabidopsis genome, there are five DELLA genes , GA-INSENSITIVE [GAI], RGA-LIKE1 [RGL1], RGL2, and RGL3), whereas rice contains one, SLENDER RICE1 (SLR1; Itoh et al, 2002). In Arabidopsis, RGA and GAI are the major repressor of GA-promoted vegetative growth and floral initiation, RGL2 is the primary DELLA during seed germination, and RGA, RGL1, and RGL2 are all involved in controlling flower development King et al, 2001;Lee et al, 2002;Cheng et al, 2004;Tyler et al, 2004). The discovery that DELLAs are nuclear localized and regulate the expression of GAresponsive genes suggests that they act as transcriptional regulators (Silverstone et al, 1998).…”

The Gibberellin perception system evolved to regulate a pre-existing GAMYB-mediated system during land plant evolution

“…I n flowering plants, gibberellin (GA) regulates the formation of the outer wall on pollen and is therefore essential for pollen development [1][2][3] . The outermost pollen wall, which is known as the exine or exospore, consists largely of sporopollenin, an organic polymer that is extremely resistant to degradation and is so durable that it has been found in microfossils that are over 500 million years old [4][5][6] .…”