Functional Identification Of Rice Auxin Influx CarrieR OsAUX3

Auxin is one of the main hormones produced by plants,and its intercellular flow depends on auxin transporters on the cell membrane.Three types of auxin transporters have been identified: AUX1/LAX,ABCB/PGP,and PIN.The AUX1/LAX influx carriers contribute to movement of IAA into the cell;The PIN efflux carriers contribute to directional movement of IAA out of the cell.The ABCB/PGP proteins mediate IAA to the outside of plasma membrane in an ATPdependent manner.In this study,a mutant osaux3 encoding auxin influx carrier was constructed utilizing CRISPR/cas9 technology in rice,and found that the mutant had more tiller numbers and lower plant height compared with wild type ZH11.The purpose of the study is to establish the relationship between auxin and rice tillering regulation,explore the molecular mechanism of OsAUX3 regulating rice tillering,and improve rice tiller regulation network.The main results are as follows:1.The expression profile of rice AUX1/LAX family showed that OsAUX1 and OsAUX5 were all expressed in different tissues,and OsAUX2 was highly expressed in inflorescence and embryo,OsAUX3 was highly expressed in culm,and OsAUX4 was highly expressed in root,culm,inflorescence and embryo.Real Time PCR andβ-galactosidase staining showed that OsAUX3 expression levels were the highest in culm and basal part,followed by root,embryo,endosperm and seeds flowering after10 days,and the lowest in axillary bud,leaf sheath,leaf and young panicle.2.Subcellular localization in rice protoplasts and tobacco indicated that OsAUX3 localized on the cell membrane.3.Compared with wild type ZH11,the tiller number of OsAUX3 knockout mutant was increased observably,the plant height was decreased significantly,and the panicle length was shorter markedly.Compared with 30 days wild type ZH11 seedlings,the elongation rate of tiller buds of OsAUX3 knockout mutant was faster,the auxin content increased significantly in basal part,and the expression levels of tiller negative regulation genes Os TB1 and D10 were significantly decreased in 0-1cm tiller buds.4.Haplotypes of OsAUX3 HAP I and HAP IV were mainly retained in japonica subspecies,while HAP II and HAP III were mainly retained in indica subspecies.OsAUX3 has obvious genetic differentiation between Indica and japonica subspecies;This gene is under selection pressure in the process of rice evolution and domestication.This study explained the reasons for the increase of tiller number of OsAUX3 knockout mutants from the perspectives of auxin concentration and transcriptional regulation,and expounded the molecular mechanism of OsAUX3 regulating rice tillering preliminarily,which laid a foundation for further mining the biological function of OsAUX3 and improving the rice tillering regulation network.