Functional Analysis Of Arabidopsis MIP2 In Vesicle Trafficking In Plant Cell

In eukaryotic cells,Transfer of proteins between organelles of inside cells mainly depends on vesicular transport.Vsicular transport includes vesicle budding,trasport,tethering,docking and fusion.The initial contact between the vesical and target membranes is mediated by tethering,tethering factors are responsible for this process.In previous study,we found MAG2 complex is a homolog of yeast Dsll complex,which may regulate the vesicular transport between the ER and the Golgi.MIP2,a subunit of MAG2 complex,its yeast and mammalian homologes play important roles in vesicle trafficking and the mechanisms underlying are mainly known.While,we know little about MIP2 in vesicular transport nor its biological function.In order to reveal the mechanism underlying ER-Golgi vesicule trafficking,further understand MAG2-complex-dependent pathway,we made a preliminary analysis of the function of MIP2 gene on vesicular transport and the effects on plant growth and development using the model plant Arabidopsis.Through the promoter activity and western analysis,we found that the expression level of MIP2 in seedlings and flowers are higher than other organells.Subsequently,we screened a MIP2 T-DNA insertion line,mip2-1,and performed a series of phenotype observation and physiological and biochemical analysis.Western blot analysis indicated that MIP2 protein was down regulated but not totally defected,and mip2-1 seeds abnormally accumulated precursors of 2S albumin and 12S globulin.Through phenotype observation,we found that root of mip2-1 seedlings were shorter then wild-type,and rosstte leaves were smaller,flowers were abnormal,and siliques were shorter..The number of mip2-1 mutant seeds in single silique was reduced,and their morphology was abnormal.Above results indicate that down regulate of MIP2 not only affects the normal transport of seed storage proteins,but also influences the growth and development of plant.Under NaCl,mannital and ABA treatment,mip2-1 was sensitive to NaCl,but not sensitive to ABA,implied that MIP2 affect the stress response pathway independence on ABA.Also,we explored the interaction sites between MIP2 and MIP1 and MIP3,we found that MIP2-C interacted with MIP1 and MIP3 through MIP2-C1 and MIP2-C2,respectively.Taken together,MIP2 plays an important role on transport of seed storage proteins,and is also involed in plant growth and development.all these results will give us a base for further study of the molecular mechanism underlying vesicular transport between the ER and the Golgi.