| Pear(Pyrus L.)belongs to the Rosaceae family and four primary varieties:white pear,sand pear,ussurian pear,and sinkiang pear are commercially cultivated in China.Among them,the sand pear is the main varieties that is widely planted in drainage areas of the Yangtze River in China.The color of skin is an important aesthetic quality in pear fruit,and the skin of the sand pear can be divided into three different types:russet,semi-russet(partial russet),and green.The skin stru cture and substance composition of sand pears with distinct colors are different.This study analyzed and compared the differences in the structure of four pearvarieties fruit with distinct colors,including ’Akibae’ ’Nijisseiki’ ’SuCui NO.1’ and’CuiYu’,and the content and composition of the main metabolites(wax,suberin,and lignin)in the skin of four selected pear varieties are compared.We performed a genome-wide identification of the KCS genes in Chinese white pear and conducted the related bioinformatic analysis.Additionally,based on transcriptome sequencing data,subcellular localization and transient over-expression,key KCS genes involved in wax and suberin synthesis were characterized.The main results are as follows:1.The analysis and comparison of the structure and substance composition of sand pear skin of different colors revealed the differences of content and composition in wax,suberin,and lignin.Observations of the pear skin anatomical structure showed that the cuticle and epidermal cells of russet and semi-russet fruit skin were ruptured and secondary suberin lamellae formed on the surface of the fruit.The cuticle of green sand pear skin remained intact,and there was no obvious suberin formation.The results of metabolite analysis showed that the content of wax,lignin and suberin in pear peel of different colors also showed significant differences.The content of suberin and lignin in russet and semi-russet pear skin was significantly higher than that in green pear skin,while the wax content in green pear skin was significantly higher than that in russet pear skin:The lignin and suberin content of russet and semi-russet pears were 2.22 and 5.13 times that of green pears,respectively,while the wax content of russet and semi-russet pears was 0.45 times that of green pears.2.Key KCS family genes involved in sand pear skin color formation were identified through genome-wide identification of the KCS family,related bio informatics analysis,and transcriptome sequencing of four different varieties of pear fruit skin.A total of 35 KCS family members were identified in Chinese white pear and the systematic evolution,gene structure,and chromosome distribution of pear KCS family were analyzed.Six KCS genes were screened and identified based on transcriptome sequencing of the four pear varieties,and the expression of relevant genes in fruit skin at different mature stages and in different tissues was analyzed.Ultimately,four candidate genes,PbrKCS15,PbrKCS19,PbrKCS24,and PbrKCS28,were selected,and the expressions of PbrKCS15,PbrKCS19,and PbrKCS24 were positively correlated with wax content in pear fruit skin of different colors,while the expression of the PbrKCS28 gene was positively correlated with suberin formation.3.The function of candidate KCS genes was verified through transient over-expression analysis in tobacco leaves and pear fruit.Overexpression of PbrKCS15 in tobacco significantly increased the wax content of tobacco leaves,while other genes had no significant effect on wax or suberin content.Overexpression of PbrKCS15,PbrKCS19,and PbrKCS24 in pear fruit significantly increased the wax content of fruit skin,but had no significant effect on suberin content,while overexpression of PbrKCS28 could promote the accumulation of suberin in fruit skin. |
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