Function Of Rice Plant Architecture Regulated By AP2 Family Transcription Factor OsRPH1

Rice（Oryza sativa L.）is one of the most important food crops for human beings,and nearly half of the population uses rice as the main food.Increasing the yield of rice is still the main purpose of the current research.The plant type of rice is closely related to the formation of rice yield.It not only can control the seed setting rate of rice,but also can affect the efficiency of photosynthesis.APETALA2/Ethylene Response Factor（AP2/ERF）is widespread in the plant kingdom and plays a vital role in the transcriptional regulation of plant growth,development,and defense responses.In this paper,a novel AP2/ERF transcription factor,OsRPH1,was isolated and functionally characterized.The molecular mechanism of OsRPH1 biological function was elucidated to provide a theoretical basis for molecular breeding of rice plant type.The main findings are as follows:Based on the amino acid similarity of the AP2 DNA binding domain,OsRPH1protein belongs to the Iva group of the AP2/ERF family,and has a potential nuclear localization signals（NLS）.OsRPH1 protein was localized in the nucleus and has transcriptional activity.At the seedling stage,the seedling height of the OsRPH1-overexpressing（OE）rice was significantly shorter than non-recipient rice variety,Kitaake:in the reproductive stage,the plant height,root weight,ear length,grain length and stem node length of OsRPH1-OE rice was significantly shorter than Kitaake.High-performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）analysis showed that the level of active GAs（GA₁,GA₃,and GA₄）was significantly decreased in OsRPH1-OE plants compared with Kitaake.By applying exogenous gibberellin GA₃,the second stem node of the OsRPH1-OE plants can be restored to the Kittake.The expression levels of gibberellin-related genes indicated that in OsRPH1-OE plants,six of GA biosynthesis genes,OsGA20ox1^OsGA20ox4 and OsGA3ox1,OsGA3ox2,were suppressed,while three of GA inactivation genes,OsGA2ox7,OsGA2ox9,and OsGA2ox10,were induced.In addition,six candidate proteins interacted with OsRPH1 were detected by rice cDNA library screening.The interaction between OsRPH1 and the blue light receptor OsCRY1b was confirmed by yeast two-hybrid and two-molecule fluorescence complementary analysis（BiFC）.Furthermore,OsRPH1-OE plants can inhibit the growth of riceunder blue light.In summary,OsRPH1 is a new AP2/ERF transcription factor in rice.It decreases the levels of active GAs by regulating the expression of GA biosynthesis and GA inactivation genes,leading to reduced plant heights.In addition,OsRPH1 interacts with the blue light receptor,OsCRY1b,however,their interaction effect on plant height will be elucidated in further studies.