Systematic Analysis Of OsIAA And OsGSK Gene Families And Characterization Of OsIAA1 In Rice

Rice(Oryza Sativa L.) is one of the most important food crops in the world. Phytohormones play critical roles in plant growth,development and response to environmental stimuli.Auxin regulates arrays of growth and developmental processes including apical dominance,lateral/adventitious root formation,tropisms,fruit set and development,vascular differentiation,and embryogenesis.Brassinosteroid(BR) also regulates a wide range of cellular and development processes such as elongation, senescence,seed germination,reproductive development,and photomorphogenesis.The signaling pathways of these two phytohormones have been intensively studied in Arabidopsis,however,relatively limited information is available in rice.This study aimed to systematically analyze two gene families in rice,OsIAA and OsGSK that plays critical roles in auxin and brassinosteroid signaling pathways respectively,and to characterize the functions of some members of the two families.The research components of this study include three parts:1) sequence analysis and expression profiling of OsIAA gene family in developmental process and in response to phytohormone and stress treatments;2) systematic analysis of glycogen shaggy-like kinase gene family in rice;and 3) characterization of a few members of OsIAA gene family including OsIAA1 gene which was identified with roles in auxin and BR responses and plant morphogenesis.The main results of OsIAA gene family analysis are as follows:1.Expression profiles for the genes of OsIAA and OsARF families have been investigated in the tissues and organs from an entire life cycle of rice.Results indicated that most of OsIAA members exhibited tissue-specific expression patterns while most of OsARF members showed constitutive expression patterns.By hierarchical analysis,eight OsIAA-OsARF co-expression gene pairs were identified. These gene pairs are possibly involved in specific developmental processes.2.Expression pattern analyses of OsLAA family genes(OsIAAs) under different phytohormones and stress treatments showed that most of the OsIAAs were induced not only by phytohormone treatment but also by abiotic stress,indicating possible involvement of OsIAAs in phytohormone and abiotic stress responses.3.Analysis of the DR5-GUS transgenic rice plant revealed that root phenotypic changes induced by mannitol is associated with the expression change of DR5-GUS,which provides direct evidence for the link between abiotic stress and auxin signaling. The main results of functional analysis of OsIAA genes are as follows:1.Expression profiling analyses by RT-PCR,reporter gene(GFP driven by OsIAA1 promoter),and real-time PCR indicated that OsIAA1 is a constitutively expressed gene.2.Over-expression of OsIAA1 in rice resulted in decreased auxin sensitivity and increased BR sensitivity in root growth.Moreover,transgenic plant exhibited dwarfism and loose plant architecture,suggesting an involvement of OsIAA1 in auxin and BR responses.3.Analysis of OsIAA1-interacting protein implied that OsIAA1 could interact with OsARF1.OsARF1 T-DNA insertion mutant(osarf1) showed similar phenotype to that of OsIAA1-overexpression plant,indicating a critical role of OsIAA1 in mediating auxin and BR signal pathway by interacting with OsARF1.4.Overexpression of OsIAA4 resulted in increased tiller angle and dwarfism,and decreased sensitivity to auxin.5.OsIAA9 is expressed only in roots and coleoptiles,and the expression pattern in the roots is similar to DR5-GUS.OsIAA9-overexpressing rice plants also showed decreased sensitivity to auxin.The main results of OsGSK gene family analysis are as follows:1.Nine members of OsGSK family,distributing on chromosome 1,3,5,6 and 9,were identified by sequence analysis.Protein sequence alignment revealed a highly conserved "kinase domain" in OsGSKs.2.High expression level was detected for most OsGSKs at different developmental stages,suggesting that different OsGSKs may play important roles at different developmental stages of rice.3.Expression profile analysis of OsGSKs under different type of phytohormones and abiotic stresses suggested that some members of OsGSK family are also involved in phytohormone and abiotic stress responses.Taken together,this study provided not only plenty of basic information on the expression profiles of OsIAA and OsGSK gene families,but also some evidence on the involvement of these two families in stress responses with crosstalk to auxin and/or BR signaling.