The Functional Verification Of Photorespiration Pathway Related Genes AT2 In Hami Melon(Cucumis Melo L.)

Melon?Cucumis melo L.?is an important economic crop in Xinjiang,and its yield is affected by many factors such as adverse conditions and pathogenic bacteria.Photorespiration is an important biological process which involved in plant growth,development,coordination of photosynthesis,and regulation of plant resistance to stress.AT2 is a resistance enzyme gene which was encoding the serine glyoxylate aminotransferase?SGAT/SGT?that the key enzyme of photorespiration pathway.It was shown that SGAT was able to influence plant growth and enhance stress through regulated expression.In this study,we used AT2 gene which from a resistant melon cultivar called‘MR1'as the research object and the overexpressed homozygous tobacco lines and transgenic melons as meterials.We measured the physiological and biochemical indicators in stress and the expression levels of AT2 gene.In this study,the AT2 gene of MR1,a resistant melon cultivar,was used as the research object.To overexpress the AT2 gene in tobacco and melon,the relevant physiological and biochemical markers and AT2 gene expression were measured under stress conditions;meanwhile,the expression level of SHMT1 and GOX that metabolic pathway-related genes were analyzed.The results of the study are as follows:?1?The optimal concentration of kanamycin for the screening homozygous lines was determined to be 150 mg/L.and finally there were three overexpressed AT2 homozygous tobacco lines were obtained.The salt stress of T₁ generation overexpressed tobacco lines showed that under salt stress the germination rate of the transformed lines was significantly higher than that of the wild type?P<0.05?,the malondialdehyde and conductivity were opposite;under salt stress the expression level of overexpressed homozygous AT2 gene was significantly higher than wild type which indicated overexpressedAT2 gene could enhance salt tolerence in tobacco.?3?The treatment of overexpressed tobacco for inoculation of brown spot disease showed that the incidence of wild type after inoculation with pathogenic bacteria was 90%,the incidence of different homozygous lines was 25%,37.5%and 32.5%which were significantly lower than wild type?P<0.05?.The expression levels of AT2,GOX,and SHMT1genes were significantly increased after susceptible,and the expression levels of AT2 and GOX in the homozygous lines were significantly higher than those in the wild type,but there was no significant difference in the SHMT1 indicated that overexpression of AT2 gene can increase resistance to brown spot disease in tobacco.?4?The optimal condition for tissue culture of the'Queen'was 6-BA 1 mg/L,the optimal condition for genetic transformation was seedling age 3 days,and the OD value was 0.5;finally,three positive melon seedlings were obtained by PCR identification and two strains were empty.?5?The bioinformatics analysis showed that the promoter region was located in the range of 69-1068 bp that contains a large number of functional elements related to adverse stress responses.The expression level of AT2 in overexpressing melon lines and MR1 were significantly higher than the Queen?P<0.01?.In the contrast,the GOX and SHMT1 genes had the highest expression in the Queen indicated that the overexpression of AT2 gene might inhibit the expression of GOX and SHMT1.After SA administration,the expression of AT2gene was significantly increased,indicating that the expression of AT2 gene was induced by SA.