Analyses Of Correlation Between MAG2 Tethering Complex And ABA Signaling Pathway

In higher plants,seeds accumulate numerous storage proteins to use as nitrogen resources for early development.Seed storage proteins(SSPs)are synthesized as large precursors on the rough endoplasmic reticulum(rER),and are delivered to protein storage vacuoles(PSVs)via vesicle transport,where they are processed to mature forms.We previously identified an Arabidopsis ER-localized tethering complex,MAG2 complex,which might be involved in Golgi to ER retrograde transport.The MAG2 complex is composed of 4 subunits,MAG2,MIP1,MIP2 and MIP3.Mutants defective on these subunits have defects on vesicle transport.The SSPs were accumulated inside the ER lumen and induced ER stress.During embryogenesis and maturation,ABA signaling plays essential role.In this study,we used mutants mip2-1,mag2-1,mip3-1,mag2-1mip3-1 and mip2-1mip3-1 which are defective on vesicle transport,and mutants abi5-7,pyl1112458,snrk2.2/2.3/2.6 and aba2-1 which are defective on ABA signaling,to preliminarily investigate the correlation between the ER-Golgi vesicle transport and ABA signaling during seed maturation,dormancy and germination.Through the phenotype observation of the whole growth cycle of the vesicle transport defective mutants,we found that the single and double mutants had shorter root length,plant height,siliques and smaller seeds.These indicated that defects on MAG2 complex subunits affected plant gro,wth and development.The accumulation of SSP precursors in the double mutants was more than that the single mutants,indicating that the vesicle transport was blocked more seriously in the double mutants.Compared with Col-0,the mutant seeds have less protein content,and reduced protein quality.Germination ratio of the mutant seeds decreased with extension of storage time,especially the double mutant seeds decreased dramatically.These results suggest that the decreased efficiency of vesicle transport affects the quality of seed proteins,which in turn affects seed longevity.Under ABA and salt treatments,the germination ratio of the MAG2 complex defective mutants decreased faster than that of the wild type,and the germination ratio of the double mutants decreased significantly,indicating that the vesicle transport mutants were sensitive to ABA and salt stress.The expression levels of transcription factors,WRKY40,WRKY41,WRXY6,FUS3,LEC2,LEC1,ABI3,ABI4 and ABI5 were also reduced in these mutants.All these suggested that the vesicle transport affects ABA signaling and relating factors.The protein accumulation of MIP1,MIP2 and MAG2 was significantly changed in ABA signaling mutants.The accumulation of SSP precursors was increased in these mutants,and the germination ratio of these mutant seeds was decreased with the extension of storage time.All these results indicated that ABA signaling affects ER-Golgi vesicle transport.Yeast two hybrid analysis indicated that SnRK2.2/2.6 and MAG2 interacted directly,suggesting that ER-Golgi transport and ABA signaling pathway are closely correlated.This need further investigation to clarify the mechanism.In this study,we explore the correlation between MAG2 tethering complex-dependent vesicle transport and ABA signaling pathway.This will contribute to clarify the mechanism underlying ABA signaling and vesicle transport interaction during seed maturation7dormancy and germination.