Function Analysis Of OsRAA1 Predominantly Expressed In Rice Root

OsRAA1(Rice ROOT ARCHITECTURE ASSOCIATED1)is a small GTP-binding protein in rice and encodes a 12.0-kD protein which has 58% homology identity to the protein AtFPF1 in Arabidopsis.The transcription of OsRAA1 is specifically in the root apical meristem,elongation zone,young lateral root and lateral root primordial.The root system plays an important role in the acquisition of water and nutrient.The length of crown root and lateral root number is of great importance to the root system architecture.Therefore,it is very essential to understand the molecular mechanism underlying root growth and development process and improve the root system architecture in rice.In this study,we preliminary investigated the biological functions of OsRAA1 by reverse genetics.To further explore the molecular mechanism,we used the yeast two-hybrid technology and analyzed the transcriptome in root tissue of OsRAA1 transgenic plants.The main results as follows:(1)Phenotype of OsRAA1 in transgenic plants indicated that both RNA interference(RNAi)and overexpression of OsRAA1 could inhibit primary root growth which forms a helix root.Overexpression of OsRAA1 produces more adventitious roots and increases lateral root density,however OsRAA1 RNAi inhibites adventitious roots length,adventitious roots number and lateral root density.This result suggested that OsRAA1 plays an important role in rice root development.(2)In flowering,the spikelet shows yellow and plump anthers and pollen have high vitality in WT plants.Whereas,abnormal expression of OsRAA1 in transgentic rice,especially in RNAi transgenic lines resulted in abnormally white and shrunken anthers,and most of the pollens have lower vitality,even no vitality.This result showed that OsRAA1 plays an important role in rice reproduction.(3)Transcriptome analysis indicated that the altere expression of OsRAA1 changed transcript levels of the related gene in both auxin and signalings.This result layed the foundation for further study of the molecular mechanism of OsRAA1 in rice root development(4)The expression of OsRAA1 was induced by auxin.After NPA treatment,the primary root and adventitious root length was inhibited in WT plants but were increased in transgenic plants.However after NAA treatment,the primary root length,adventitious root length and number,lateral root density of WT and trangenenic rice were seriously inhibited.This result suggested that OsRAA1 might regulate the development of rice root by affecting the auxin homeostatis.(5)The results of ROS analysis showed that,after PEG,mannitol and NaCl treatment,the difference of roots between wild type and transgenic plant decreased.The content of ROS in wild type and transgenic plants is higher than that in untreated plants,and the content of ROS in transgenic plants are higher than wild type either in treated or untreated experiments.DAB and NBT staining results are consistent with with PEG mannitol or NaCl treatments.There results indicated that OsRAA1 affectes rice root development by affecting the content of ROS.(6)Nine candidate proteins that may interact with OsRAA1 were screened by yeast two-hybrid system.Among them the peptidyl-prolyl cis-trans isomerase and cinnamyl alcohol dehydrogenase are related to auxin signal transduction and reactive oxygen species production,respectively.This result further suggests that OsRAA1 is involved in the rice growth mediated by auxin or(and)ROS signalling.