Study On The Mechanism Of PpyMYB144 Regulating The Formation Of Suberin In Pear Rust Wood

Pyrus is a deciduous fruit tree native to China,mainly divided into four types:white pear（Pyrus bretschneideri）,sand pear（Pyruspyrifolia）,Qiuzipear（Pyrus ussuriensis）and Western pear（Pyrus communis）.Among them,’Cuiguan’ is the largest and most widely distributed sand pear variety in China.In the middle and lower reaches of the Yangtze River,the fruit development season of ’Cuiguan’ pears coincides with rainy and high humidity,and rust spots are easily formed on the surface of the fruit,which seriously affects the appearance quality of the fruit and reduces the commerciality of the fruit.Suberin is the main component of pear fruit rust.Fruit bagging can reduce the occurrence of pear fruit rust by inhibiting the expression of genes related to suberin synthesis.In this paper,the ’Cuiguan’ pear peel was used as the test material,combined with the bagging treatment to slow down the formation of rust,to observe the structural differences of the untreated（rust）and bagged（without rust）pear peels during fruit development,and to analyze the related substances Content differences;based on transcriptome sequencing data,focusing on members of the PpyMYBs transcription factor family,through gene expression analysis,evolution analysis,dual luciferase experiments and tobacco transient overexpression functional verification,etc.,to analyze and identify the key PpyMYBs members involved in pear fruit rust formation,the result is as follows:1.The occurrence of fruit rust and the change of suberin content in untreated and bagged pears during fruit development were clarified.During the fruit development of’Cuiguan’ pear,the accumulation of fruit rust was mainly in the middle and late stages of fruit development.Through the observation of ripe pear peel slices and staining,it was found that compared with the non-rust pear peel,the rust pear peel had a thin and incomplete cuticle,and there was an obvious cork layer under it,and the outermost of the cork layer had yellow-brown accumulation;The increase of total content was significantly related to the occurrence of pear fruit rust.Among the various suberin monomer components,the content of α,ω-dicarboxy fatty acids was significantly higher than that of other suberin monomer components,which accounted for the rust of pear fruit.35%of the total amount of suppository.2.Based on the transcriptome sequencing data of untreated and fruit bagged pear peels,screened to obtain multiple differentially expressed PpyMYBs transcription factors,and analyzed the expression patterns of related genes during pear fruit development,PpyMYB34,PpyMYB138,PpyMYB138L,PpyMYB139,PpyMYB144 gene expression gradually increased during the formation of pear fruit rust,and fruit bagging treatment could significantly inhibit the expression of related genes.At the same time,the expression of structural genes PpyCYP86A1 and PpyCYP86B1,which regulate the synthesis of suberin α,ω-dicarboxy fatty acid components in pear peel,were significantly correlated with the formation of pear rust.3.The mechanism of PpyMYB144 regulating suberin in pear peel was clarified.Using the dual luciferase experimental system,it was found that PpyMYB34,PpyMYB138,PpyMYB138L and PpyMYB139 had no regulatory effect on the PpyCYP86A1 and PpyCYP86B1 promoters,and PpyMYB144 could transcriptionally activate the PpyCYP86B1 promoter activity.The results of promoter-binding element analysis showed that there is an AC element bound by MYB transcription factor in PpyCYP86B1,and PpyMYB144 has no obvious regulatory effect on the PpyCYP86B1 promoter of the mutant AC element,indicating that PpyMYB144 specifically binds and activates the AC element of the PpyCYP86B1 promoter.Overexpression of PpyMYB144 in tobacco significantly increased the suberin synthesis-related NtCYP86B1 gene and suberin content.In summary,this study found a transcription factor PpyMYB144 involved in the regulation of suberinization of ’Cuiguan’ pear fruit rust.PpyMYB144 activates the suberin synthesis structural gene PpyCYP86B1,and promotes the suberin monomer α,ω-dicarboxyl group.Fatty acid accumulation,which in turn regulates the formation of fruit rust.