Phenotype Analysis Of Oxysterol-binding Protein (OSBP)-related Protein Mutant Abr1 In Arabidopsis

Oxysterol-binding protein (OSBP)-related proteins (ORPs) are lipid-binding proteins. They participate in many plant physiological processes including singaling transduction, vesicular trafficking, lipid metabolism, and nonvesicular sterol transport.Here we identified an Arabidopsis T-DNA insertion mutant ABA resistant 1(abr1) from OSBP family. The mutant showed wider shoulder of the silique, rounder rosette leaf, and less sensitive to Abscisic acid compared with wide type.As the phenotypes of abrl mutant is similar to those of agbl-2(the G protein mutant), we introduced the abrl mutation into the single mutant agbl-2 and double mutant agbl-2/gpal-4. The double mutant agbl-2/abrl and the triple mutant agbl-2/gpal-4/abrl showed more severe morphological phenotypes than their parents. But the sensitivity phenotype to ABA treatment of agbl-2/abrl and agbl-2/gpa 1-4/abrl tends to be similar to those of the two G protein mutants. These results indicate that both ABR1 and G proteins control the morphological development of siliques and leaves in the different pathways. However, further study is needed to the function of ABR1 in ABA signaling pathway. The shortened siliques and leaves in ABR1 over-expression lines are more remarkable than in abrl. Furthermore, they are more sensitive to ABA.The ABR1 was found to be expressed in the various tissues tested by histological localization analysis, such as in roots, stomates, stem meristem and siliques. The confocal data suggested that the subcellular localization of YFP-ABR1 might be in the endoplasmic reticulum and plasma membrane. The result of yeast two-hybrid showed that ABR1 could interact with VAP27 in vitro.Altogether, we propose primarily that ABR1 participates in the ABA singaling pathway and regulates the development of siliques and leaves mediated by unknown intracellular signal molecule trafficking.