Function And Mechanism Of Maize Methionine Sulfoxide Reductase ZmMSRB1

High salt and drought are two major factors limiting crop yield.Therefore,it is one of the main directions in crop breeding to characterize new genes with stress-resistance function and analyze their mechanism.The plant MSR gene family can repair the oxidative damage of intracellular macromolecules,so they play an important role in plant response to stress.Corn is one of the main crops in China,but the functions of its MSR gene family is rarely reported.Our previous studies showed that ZmMSRB1 could be induced by NaCl and PEG,so we hypothesized that ZmMSRBl might play an important role in plants' response to salt stress.The main research contents of this thesis include:1.Functional analysis of ZmMSRB1 geneZmMSRB1 protein is located in chloroplast and the results of multiple sequence alignment showed that this gene had high homology with MSRB1 from sorghum,wheat and Brachypodium.The results of conserved domain analysis showed that this protein has SelR domain which is unique to MSRB sub-family,and combined with enzymatic properties analysis experiment,it was proved that ZmMSRBl belonged to MSRB sub-family.The results of promoter analysis show that there are a large number of light and stress response elements in the ZmMSRB1 promoter region,which is consistent with the results of sub-cellullar localization and induced expression.The germination experiments of overexpression of ZmMSRB1 in Arabidopsis showed that ZmMSRB1 did not affect the early germination of Arabidopsis.The phenotypic experiments showed that the overexpression of ZmMSRB1 could significantly enhance the resistance of Arabidopsis to salt,osmotic and oxidative stresses.2.Analysis of ZmMSRB1 stress resistance mechanismOverexpression of ZmMSRB1 in Arabidopsis significantly reduced the accumulation of ROS.Further,the expression level of ROS producing and scavenging genes was detemined.Compared with wild type,the expression level of ROS producing genes in overexpression lines were significantly decreased,while ROS scavenging genes were opposite.At the same time,the enzyme activity of ROS scavenging enzymes such as SOD,CAT and POD in the overexpression lines was significantly higher than that in wild type,while the content of H2O2 and MDA was also significantly reduced.The results showed that ZmMSRB1 expression could regulate the balance of ROS in Arabidopsis.Our results also showed that ZmMSRB1 could promote the expression of SOS genes and maintain the intracellular K+/Na+ balance,thus improving the salt tolerance of Arabidopsis.On the other hand,overexpression of ZmMSRB1 can significantly promote the expression of key gene in the proline and the glucose synthesis,and also increase the content of proline and soluble sugar in Arabidopsis.The above results show that ZmMSRB1 is involved in the process of plant response to abiotic stress by different mechanism.According to the previous studies,the interaction was tested between ZmMSRB1 and ZmGSTF8 by yeast two hybridization.The total GST activity was measured and the expression level of AtGSTF8 gene of Arabidopsis was also determined under salt stress treatment.Compared with wild type,the total GST activity of overexpression lines were significantly enhanced,and the expression level of AtGSTF8 gene was also significantly improved.In addition,the phenotypic results of exogenous BSO added showed that exogenous BSO could partially limit the stress-tolerance phenotypes of transgenic Arabidopsis by ZmMSRB1.These results indicated that ZmGSTF8 might be one of the substrate of ZmMSRB1,and the salt tolerance of ZmMSRBl transgenic arabidopsis partly depends on the function of ZmGSTF8.