Functional Characteristics On E3 Ubiquitin Ligase SRAR1 In Arabidopsis

Ubiquitination plays important roles in regulating diverse cellular process in plants,including perception and signal transduction of various hormone and external environmental signals.Abscisic acid(ABA) is required for regulating not only plant growth and development,but also plant response to abiotic stresses as signaling sensor.Recent studies suggest that ubiquitination also plays crucial roles in plant response to abiotic stress and the phytohormone abscisic acid(ABA).It is of great importance to reveal the mechanism of stress-related and phytohormone signal pathways in plants.In this study,take advantage of strategies on biochemistry, molecular biology and genetics,we describe a novel RING finger E3 ubiquitin ligase, SMALL RNA-PRODUCING AND ABIOTIC STRESS-INDUCED RING FINGERI(SRAR1),which function as a key regulator in stress-related ABA signaling during abiotic stress in Arabidopsis.We found that the Arabidopsis SRAR1 transcript was strongly induced by dehydration,NaCl stress and ABA treatment.And dehydration-induced accumulation of SRAR1 mRNA was significantly reduced in aba2-1,abi1-1 and abi2-1.We demonstrated that SRAR1 showed E3 ubiquitin ligase activity in vitro and the intergrity of the RING motif was required for its activity.SRAR1 mainly located in the nucleus and weakly outside the nuclear compartment.SRAR1-promoter::GUS analysis showed that SRAR1 was highly expressed in vascular tissues and guard cells. Overexpression of SRAR1 in Arabidopsis led to ABA hypersensitivity in germination and postgerminative growth stages and ABA-related phenotypes,including salt hypersensitivity in germination,enhanced ABA-induced stomatal closure,and increased drought tolerance.Overexpressing SRAR1-mut plants did not show salt hypersensitivity in germination and postgerminative growth stages,demonstrating that the ABA-related phenotypes are due to the overexpression of SRAR1.We also detected a 21bp small RNA signal produced from 3'-UTR of SRAR1,whose biogenesis is dependent on hen1 and hyl1.Microarray analysis indicated that SRAR1 was crucial for the expression of a number of stress-responsive genes.Thus,our results indicate that SRAR1 is a positive regulator of ABA signaling and it might serve as a drought tolerance engineering candidate gene for its promising application in crop plants.