Study Of Key Sorbitol Transporters In Regulating The Occurrence Of Watercore Of Pyrus Pyrifolia

Watercore is a common physiological disease of pear fruit,which is closely related to environmental factors such as high temperature.When the watercore of pear fruit is serious,it will lead to the corruption of the pulp,which will affect the edible value and storage quality of the pear fruit after harvest.Previous studies have found that the excessive accumulation of sorbitol in the intercellular space of pulp is an important reason for the formation of watercore,but the molecular mechanism of pear watercore has not been studied.In order to further explore the molecular mechanism of sorbitol transport in regulating the occurrence of watercore,this study used sand pear varieties with different resistance to watercore as materials to analyze the relationship between sorbitol transporter and the formation of watercore,and identified key genes for functional verification.The result is as follows:（1）Transcriptome sequencing of ’Akibae’ diseased fruit was performed,and it was found that there were 5218 genes and 1732 genes in watercore fruit with significantly up-regulated and down-regulated expression.Among them,the gene expression of enzymes related to cell wall degradation was significantly increased,and the expression of ethylene synthesis genes and abscisic acid synthesis genes was significantly increased,which indicated that the increase of ethylene and abscisic acid content in watercore fruit led to the degradation of cell wall.In addition,one sorbitol synthesis gene was significantly up-regulated,while the expression levels of two sorbitol decomposition-related genes and four sorbitol transporter genes were significantly decreased in watercore fruit.（2）PpSOT3 was expressed in different tissues and organs of ’Akibae’ pear,’Hosui’pear and ’Aikansui’ pear.Among them,the watercore resistant cultivar ’Aikansui’ was mainly expressed in young leaves and young fruits,and in ’Hosui’ pear and ’Akibae’ pear susceptible to watercore,it was mainly expressed in young leaves and mature fruits.By applying a sugar alcohol transport inhibitor（p-chloromercuric acid,PCMBS）to young fruits in vivo,it was found that all three varieties were obviously water-stained,the transcription level of PpSOT3 in the pulp was significantly reduced,and the content of sorbitol in the intercellular space was significantly increased high.The results further indicated that the expression of PpSOT3 was inhibited in late fruit development of sand pear cultivars prone to watercore,which may be an important reason for the difference in resistance among different cultivars.（3）The results of subcellular localization analysis showed that PpSOT3 was located in the cell membrane.PpSOT3 overexpression vector was injected with Agrobacterium tumefaciens into pears,and it was found that the expression of PpSOT3 was significantly increased,and the content of sorbitol in the intercellular space was significantly decreased.The alcohol content increased,and the pear pulp appeared water-soaked.The above results indicate that PpSOT3 is localized to the cell membrane and has the function of transmembrane transport of sorbitol.In conclusion,PpSOT3 is a PCMBS-sensitive sorbitol transporter located on the cell membrane,its expression is inhibited and its activity is reduced,which leads to the accumulation of sorbitol in the intercellular space of fruit,which directly causes the occurrence of watercore.This study will provide a theoretical basis for the research on the occurrence mechanism of pear watercore,and provide genetic resources for the prevention and treatment of watercore.