Preliminary Study On Roles Of Phytochrome-interacting Factor OsPIL14 In Rice Growth And Development

PIF transcription factors(phytochrome-interacting factors)are key components of phytochrome-mediated light signaling pathways.It was predicted that there are six candidate genes encoding PIF transcription factors in rice genome,designated as OsPIL11 to OsPIL16 At present,there have few reports about functions of PIFs in light signal transduction and in regulating rice growth and development,which greatly limits the understanding and application of light signal pathways of monocotyledons.In this study,we analyzed the structural features,subcellular localization of OsPIL14 protein and expression patterns of OsPIL14 gene.Moreover we also produced both overexpressed and loss-of-function transgenic lines of OsPIL14-,in order to reveal the roles of OsPIL14 in rice growth and development.The main results are as followed:(1)OsPIL14 protein was predicted to be a type of bHLH transcription factor using bioinformatics and other methods.OsPIL14 contains a bHLH domain,an APB domain,and a nuclear localization sequence(NLS).Subcellular localization results showed that OsPIL14 protein localizes to the nucleus.However,the interaction between OsPIL14 and rice phytochromes was not detected using the yeast two-hybrid assay in this study.(2)Both red light(R)and far-red(FR)light induced the expression of OsPIL14.Analysis of OsPIL14 transcript levels in wild type,phyB mutants and phyAphyB double mutants grown under dark and continuous R conditions showed that phyB and other phytochromes(probably phyA)were able to sense red light to induce OsPIL14 expression.Meantime,we also compared the transcript levels of OsPIL14 among the wild type,phyA mutant and phyAphyC double mutants grown under dark and continuous FR conditions.It was found that phyA and phyC perceive far-red light to induce expression of OsPIL14.Therefore,OsPIL14 is probably involved in phytochrome-mediated R and FR light signaling pathways.(3)Quantitative Real-time PCR analysis of the expression level of OsPIL14 in the different tissues and organs of wildtype showed that OsPIL14 was mainly expressed in leaves,especially flag leaves.(4)Comparing the phenotypes of wild type and OsPIL14 transgenic rice lines grown in dark conditions revealed that overexpression of OsPIL14 can promote the elongation of mesocotyles in rice seedlings,but inhibit coleoptile elongation.(5)We compared photomorphogenesis of wild type and OsPIL14 transgenic seedlings grown under either R or FR light conditions.The results showed that overexpression of OsPIL14 gene resulted in elongation of coleoptiles and the first incomplete leaf relative to wild type.These results suggest that overexpression of OsPIL14 caused the insensitivity to either R or FR.Therefore OsPIL14 is involved in R or FR-mediated photomorphogenesis.(6)Overexpression of OsPIL14 gene can lead to significant increase in plant height,slenderer leaf blade,larger leaf angle,and exposed internnodes compared with wild type.Moreover,OsPIL14 is also involved in the regulation of panicle architecture,for example,affecting seed grain length,grain width,and 1000-grain weight and other grain traits.(7)The salt-tolerance assays suggest that the OsPIL14-CRISPR lines exhibited reduced salt tolerance compared to wild type when being treated with 200 mM NaCl solution.These results suggest that OsPIL14 is also involved in rice salt stress responses although the mechanism is elusive in this study.In summary,the rice phytochrome interaction factor OsPIL14,encoding one bHLH type transcription factor,is involved in phytochrome-mediated light signal pathway to affect photomorphogenesis.OsPIL14 plays very important roles in rice growth and development.This study not only provides a cue for dissecting light signal transduction pathways in rice and other monocotyledons,and also lays a theoretical basis for genetically improving agronomic traits in rice.