Brassinosteroid Regulates Cell Elongation by Modulating Gibberellin Metabolism in Rice    

Abstract

Brassinosteroid (BR) and gibberellin (GA) are two predominant hormones regulating plant cell elongation. A defect in either of these leads to reduced plant growth and dwarfism. However, their relationship remains unknown in rice (Oryza sativa). Here, we demonstrated that BR regulates cell elongation by modulating GA metabolism in rice. Under physiological conditions, BR promotes GA accumulation by regulating the expression of GA metabolic genes to stimulate cell elongation. BR greatly induces the expression of D18/GA3ox-2, one of the GA biosynthetic genes, leading to increased GA 1 levels, the bioactive GA in rice seedlings. Consequently, both d18 and loss-of-function GA-signaling mutants have decreased BR sensitivity. When excessive active BR is applied, the hormone mostly induces GA inactivation through upregulation of the GA inactivation gene GA2ox-3 and also represses BR biosynthesis, resulting in decreased hormone levels and growth inhibition. As a feedback mechanism, GA extensively inhibits BR biosynthesis and the BR response. GA treatment decreases the enlarged leaf angles in plants with enhanced BR biosynthesis or signaling. Our results revealed a previously unknown mechanism underlying BR and GA crosstalk depending on tissues and hormone levels, which greatly advances our understanding of hormone actions in crop plants and appears much different from that in Arabidopsis thaliana.

Dynamic Cytology and Transcriptional Regulation of Rice Lamina Joint Development

“…The expression synchronicity of GA-and BR-related genes may be due to the fact that they both promote cell elongation and to the complicated cross talk between them in rice (Tong et al, 2014). Similar to GA, decreased expression of an ABA biosynthesis gene (ABA4) and increased expression of a metabolic gene (ABA8OX1) may lead to a decreased active ABA level at later stages.…”

“…Interestingly, most auxin-related mutants present changed BR sensitivity (Song et al, 2009;Zhao et al, 2013;Zhang et al, 2015), and the inclination by treatment with brassinolide alone is suppressed by an inhibitor of IAA transport (Cao and Chen, 1995) or promoted by additional IAA (Han et al, 1997), suggesting a complex regulation of phytohormones in lamina joint development. In addition, BR-induced leaf inclination is accompanied by ethylene production and inhibited by an inhibitor of 1-aminocyclopropane-1-carboxylic acid oxidase (Cao and Chen, 1995) or suppressed by treatment with abscisic acid (ABA) and gibberellin (GA) (Han et al, 1997;Tong et al, 2014), further indicating that phytohormones synergistically and antagonistically regulate lamina joint development and leaf inclination.…”

OsmiR396d Affects Gibberellin and Brassinosteroid Signaling to Regulate Plant Architecture in Rice

“…And their crosstalk differs depending on hormone concentrations, development stages, tissues, and species (Tong and Chu, 2016;Unterholzner et al, 2016). BR signaling-defected mutants are impaired in GA biosynthesis in Arabidopsis and rice (Tong et al, 2014;Unterholzner et al, 2015). Expression of GA biosynthesis gene GA20ox1 under the promoter of BRI1 in bri1-301 mutant can rescue most of its defects (Unterholzner et al, 2015).…”

“…Expression of GA biosynthesis gene GA20ox1 under the promoter of BRI1 in bri1-301 mutant can rescue most of its defects (Unterholzner et al, 2015). Arabidopsis BES1 and rice OsBZR1 can bind the promoters of GA biosynthesis or inactivation genes to regulate GA biosynthesis (Tong et al, 2014;Unterholzner et al, 2015). On the other hand, GA regulates BR biosynthesis at the transcription level.…”

“…For example, the erect leaf rice mutant, osdwarf4-1, which is partially deficient in biosynthesis of brassinosteroid (BR), can improve biomass production and grain yield under dense planting conditions without extra fertilizer . Gibberellin (GA) and BR are two predominant plant hormones that determine plant height and leaf angle by regulating cell growth (Tong et al, 2014;Zhang et al, 2014). GA is perceived and bound by the soluble protein GIBBERELLIN INSENSITIVE DWARF1 (GID1), which results in GID1 conformation change; thus, the interaction of GID1 and DELLA proteins (GA response repressors) is promoted (Ueguchi- Tanaka et al, 2007;Hedden and Sponsel, 2015).…”