Involvement of phytochromes in gibberellin-mediated photomorphogenesis in rice seedlings

Abstract

Gibberellin (GA) is an important plant hormone, which, together with phytochrome-mediated light signals, regulates Arabidopsis thaliana development. However, roles of GA and its interaction with phytochromes in mediating skotomorphogenesis and photomorphogenesis remain unclear in rice. In the present study, the lengths of coleoptiles, seminal roots and up-ground parts were measured in either dark- or white light-grown seedlings treated with GA biosynthesis inhibitor PAC in wild type and rice phytochrome mutants. Meantime, transcript levels of light-regulated genes LHCB were also analyzed. It was observed that PAC treatment caused the inhibition of coleoptile elongation and induction of LHCB genes in dark-grown seedlings. Moreover phyA mutant exhibited less sensitive to PAC than wild type and phyB mutant in dark-grown seedlings. In white light-grown seedlings, growth of up-ground parts was inhibited by PAC while phyB mutant exhibited less sensitive than wild type and phyA mutant did. In addition, phyB antagonistically affect the inductive responses of root elongation triggered by PAC in light-grown seedlings. These results suggest that GA is necessary to maintain skotomorphogenesis and to suppress photomorphogenesis in dark-grown rice seedlings. In addition, phyA and phyB either negatively or positively affect responses caused by PAC treatment in rice seedlings. For the first time, our findings reveal the interaction between phytochrome- and GA-mediated pathways which lays the foundation for dissecting the molecular mechanism of coordinated regulation of rice development by light and GA.