A Novel Class of Gibberellin 2-Oxidases Control Semidwarfism, Tillering, and Root Development in Rice

Abstract

Gibberellin 2-oxidases (GA2oxs) regulate plant growth by inactivating endogenous bioactive gibberellins (GAs). Two classes of GA2oxs inactivate GAs through 2b-hydroxylation: a larger class of C 19 GA2oxs and a smaller class of C 20 GA2oxs. In this study, we show that members of the rice (Oryza sativa) GA2ox family are differentially regulated and act in concert or individually to control GA levels during flowering, tillering, and seed germination. Using mutant and transgenic analysis, C 20 GA2oxs were shown to play pleiotropic roles regulating rice growth and architecture. In particular, rice overexpressing these GA2oxs exhibited early and increased tillering and adventitious root growth. GA negatively regulated expression of two transcription factors, O. sativa homeobox 1 and TEOSINTE BRANCHED1, which control meristem initiation and axillary bud outgrowth, respectively, and that in turn inhibited tillering. One of three conserved motifs unique to the C 20 GA2oxs (motif III) was found to be important for activity of these GA2oxs. Moreover, C 20 GA2oxs were found to cause less severe GA-defective phenotypes than C 19 GA2oxs. Our studies demonstrate that improvements in plant architecture, such as semidwarfism, increased root systems and higher tiller numbers, could be induced by overexpression of wild-type or modified C 20 GA2oxs.

Regulation of Strigolactone Biosynthesis by Gibberellin Signaling

“…Therefore, the result that Tanginbozu displayed a GR24-insensitive phenotype suggests the possibility that the SL signal is saturated with the accumulated SL in Tanginbozu. However, the overexpression of GA 2-oxidase also positively regulated the number of tillers, indicating the importance of GA signaling in shoot outgrowth in rice (Lo et al, 2008). Further physiological studies may contribute to the elucidation of the mechanism of shoot outgrowth.…”

“…GA-deficient mutants show increased tiller bud outgrowth and dwarfism (Lo et al, 2008;Ito et al, 2010). To evaluate the effects of SL on GA-deficient rice, we used the GA-deficient mutant Tanginbozu.…”

“…However, contradicting results have been reported in which SLs act independently of GAs in stimulating internode elongation in the pea (Pisum sativum; de Saint Germain et al, 2013). Therefore, there is as yet no physiological evidence of the existence of cross talk between the GA and SL signaling pathways, although Lo et al (2008) reported that GA deficiency promotes tiller bud elongation in rice.…”

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

“…GA biosynthesis/turnover, signaling, and expression of GA-responsive genes have been associated directly or indirectly with variation in shoot branching (Lo et al, 2008;Mauriat et al, 2011;Ni et al, 2015). Genes encoding GA2ox1 were expressed at 7-fold to 18-fold higher levels in phyB-1 buds compared to wild-type at all time points examined (Fig.…”

Molecular mechanism of strigolactone perception by DWARF14

“…The Arabidopsis gibberellin (GA) biosynthetic mutant ga1-3 exhibits enhanced shoot branching, and the overexpression of GA 2-oxidase genes in rice, in which GA levels are reduced, promotes tillering 32 . These results suggest that GAs regulate branching together with or without SLs.…”