Molecular Mechanism Of G Prrotein β Subunit AGB1 Regulating Salt Stress Tolerance In Arabidopsis

The heterotrimeric GTP-binding proteins(G-proteins)consist of α,β and γ subunits and receive ectocytic signaling by interacting with G-protein-coupled receptors(GPCR),and the signaling are further tranduced into the cytoplast through appropriate downstream effectors.G protein play important role in signaling transduction in cells.In plant,it was reported that G proteins participated in many important signaling pathways such as plant development,hormone response,pathogen defense response and abiotic stress response,whereas the function of G protein under salt stress condition had not been reported.In this research,we compared the phenotype,physiological indexes and expression profile of some stress-related genes between Arabidopsis wild type(Col-0)and AGB1 deficient mutants agb1-2 under high salt stress,and we also analyzed the regulation mechanism of AGB1 under high salt stress.The major findings are as follows:1.Gene expression analysis showed that,AGB1 was down-regulated under cold and heat stresses,whereas up-regulated under high salt stress;2.Under high salt stress condition,agb1-2 mutant was hypersensitive to high salt stress,and the cotyledon green,fresh weight,germination rate and survival rate of agb1-2 mutant decreased compared to Col-0,and the root length in agb1-2 was shorter than in Col-0;3.Results of physiological indexes testing showed that exposed to salt stress chlorophyll content,proline content,POD(peroxidase)activity,Na+ content and K+ content in agb1-2 were lower than those in Col-0.However,MDA content and the concentration ratio of Na+/K+ were higher compared to Col-0,suggesting that AGB1 positively regulated high salt tolerance in plant;4.The expression analysis of stress-related genes showed that compared to Col-0,some MAPK kinase(mitogen-activated protein kinase)genes,and the other genes involving in ABA response,stress response,ion channel,proline synthesis or oxidative stress response were lower in agb1-2.Those genes involve in physiological processes that were tested in this research and results were showed in part 3.Those results indicated that these genes might be downstream genes of AGB1 and regulate high salt tolerant response through controlling above physiological process in Arabidopsis;5.In order to further reveal the molecular mechanism of AGB1,we conducted two yeast hybrid,BiFC(bimolecular fluorescence complementation)and protein pull-down assay in vitro to verify the interaction between AGB1 and MAPK1,suggesting that MAPK1 may also involved in AGB1 regulating salt stress response,whereas the detail mechanism needed further study.Taken together,in this research,we identify the phenotype and physiological indexes of AGB1 mutants under salt stress,and firstly identified that AGB1 positively regulate salt stress tolerance in plant;We study genes expression of the putative downstream and interacting protein of AGB1,preliminary reveal the molecular mechanism of AGB1 regulating high salt stress tolerance in plant.These studies gave novel way to further dissect the molecular mechanism of plant stress resistance regulated by G protein complex.