Molecular Mechanism Of Sorbitol Dehydrogenase Genes PpSDH3 And PpSDH9 Regulating The Occurrence Of Watercore In

Watercore is a kind of physiological disease in pear and apple.The flesh color browning,bitter taste,and easy to rot after harvest seriously affect the edible value and storage quality of pear fruit.In order to further explore the molecular mechanism of the occurrence of watercore,we identified the sorbitol dehydrogenase genes PpSDH3 and PpSDH9 through the expression analysis of fruits at different development stages and watercore fruits,and verified their functions and transcriptional regulation through subcellular localization analysis,transient overexpression,transcriptome sequencing,yeast one hybrid and double luciferase experiments.The results are as follows:(1)Sorbitol content in ’Akiba’ and ’Aikansui’ fruits decreased continuously at the late stage of fruit development,and the activity of sorbitol dehydrogenase was the lowest at 75 days after flowering the content of sorbitol increased significantly and the activity of sorbitol dehydrogenase decreased significantly.The expression levels of PpSDH3 and PpSDH9 genes were high abundantly expressed during fruit development,while the expression levels of PpSDH3 and PpSDH9 genes were significantly decreased during fruit development.After boron treatment,sorbitol content in ’Aikansui’ fruit decreased significantly,and the expression of PpSDH3 and PpSDH9 genes increased.These results suggest that PpSDH3 and PpSDH9 are important functional genes in sorbitol metabolism and participate in the regulation of the occurrence of watercore.(2)The results of subcellular localization showed that both PpSDH3 and PpSDH9 were located in the cytoplasm.The expression levels of PpSDH3 and PpSDH9 were significantly increased and the content of sorbitol was significantly decreased after Agrobacterium tumefaciens containing the overexpression vectors of PpSDH3 and PpSDH9 were injected into young pear fruits.These results indicate that PpSDH3 and PpSDH9 are two sorbitol degrading genes located in cytoplasm.(3)The differentially expressed transcription factor PpMYB62 was screened by transcriptome sequencing of ’Akiba’ and ’Aikansui’.Yeast one hybrid verification showed that there was interaction between PpMYB62 and the promoters of PpSDH3 and PpSDH9.Double luciferase test showed that PpMYB62 could Positive regulate the activation of the promoter functions of PpSDH3 and PpSDH9.These results indicate that PpMYB62 can positively regulate the expression of PpSDH3 and PpSDH9 genes.In summary,the expression of PpSDH3 and PpSDH9 is positively regulated by PpMYB62,which plays a key role in the regulation of sorbitol degradation during the development of Pyrus pear.The inhibition of PpSDH3 and PpSDH9 expression is the key reason for the occurrence of watercore.