The Study Of The Relationship Between Soluble Carbohydrate And Marssonina Coronaria Resistance In Apple Leaves

Apple brown spot disease(Marssonina mali)is one of the most important diseases of apple trees' growing season in China,which lead to fruit tree leaves early fall,seriously affect the yield and quality of apple.Sugar as important energy and structural substance is also important in signal transduction and osmotic regulation.Also regulates the expression of thousands of genes and participates in plant response to pathogen.In order to elucidate the relationship between sucrose / sorbitol and leaf spot resistance in apple,we studied the changes of soluble sugar content and the expression of key genes in carbohydrate metabolism after inoculated with Marssonina coronaria.Also,we used decreased of sorbitol / sucrose transgenic apples and different carbon feeding leaves to verify the effect of Marssonina mali resistance.The main results were as follows:1.The content of sugar and sugar metabolism in leaves of susceptible cultivar 'Pacific rose' and disease resistance cultivar 'Shandingzi' showed that after inoculated,the sucrose and glucose contents in leaves of 'Pacific Rose' were increased first and then decreased,and higher than those of the un-inoculated,but there was no obvious changes in 'Shandingzi'.The expression of SWEET genes were decreased in both cultivars,and the expression of MdSWEET1.1 / 1.2,MdSWEET2.4,MdSWEET3.9 and MdSWEET3.10 in 72 h were significantly lower than that of 24 h.The expression of MdSDH1 and MdSPS showed up-regulated with the inoculated time going,and the expression of MdSPS increased significantly.These results indicated that the inoculation of Marssonina coronaria had different effects on the sugar content of different resistance leaves,and had more influence on susceptible cultivar.key genes of sugar metabolism may also be involved in the regulation of resistance to Marssonina coronaria.2.For further study the function of sucrose and sorbitol in resistance of Marssonina coronaria,Decreasing of sorbitol and sucrose transgenic apple and different carbon feeding leaves' resistance were analyzed.The results showed that compared with the wild type,the content of sorbitol were decreased,and the sucrose were increased of sorbitol-synthesis-inhibited transgenic lines,and the expression of the resistance gene was down-regulated.Meanwhile,the content of sorbitol in the leaves of the sucrose-synthesis-inhibited transgenic apple was increased and the content of sucrose was decreased,the resistance gene was significantly down-regulated.This indicated that the resistances to Marssonina coronaria in different transgenic lines were different,and the regulation might be through the mechanism other than disease resistance genes.Carbon feeding leaves further showed that the incidence of apple brown spot disease was increased after feeding with sucrose,while was lighter after feeding with sorbitol.Meanwhile,the expression of disease-resistance gene was lower than that of ck leaves after feeding with sucrose and sorbitol.These results shown that increased of sucrose reduced the leaf resistance,on the other hand,sorbitol may be involved in the resistance to apple brown spot disease,but the mechanism is independent to the expression of disease resistance gene.3.In order to determine the relationship between content of sugars & alditols and the resistance of different germplasm resources to Marssonina coronaria,based on the evaluation of disease resistance of the team research.The content of soluble sugar and acid of 33 wild and 15 cultivar germplasms were determined,along with its correlation to disease resistance.The results showed that there was no significant correlation between the content of sorbitol,sucrose,glucose and malic acid in the wild or cultivar germplasm,but the correlation of sorbitol was higher than that of sucrose.4.The expression of SUSY gene was induced by the inoculation of Marssonina coronaria,in order to analyze SUSY on sugar metabolism and disease resistance in apple.The structure and expression of SUSY gene family in apple genome was analyzed.Results showed that 11 MdSUS genes in apple were divided into three types: SUS I,SUS II and SUS III,with 10-14 introns.The expression patterns of MdSUSY were diverse in different tissues and fruit development of apple,and MdSUS2.1 was highly expressed in fruit.The expression of MdSUSY1-4 was induced obviously by Marssonina coronaria.These results suggest that different MdSUS genes may play a different role in sugar metabolism and sugar utilization between source and sink.