Characterization of the composition and gene expression involved the shikimate pathway in the exocarp of ‘Dangshansuli’ pear and its russet mutant

‘Dangshansuli’ pear is a yellow–green fruit when mature, whereas that of the mutant ‘Xiusu’ is russeted. In this study, the contents of glucose, fructose and sucrose in the exocarp of ‘Xiusu’ were found to be lower than those in ‘Dangshansuli’ at 75–100 days after full bloom (DAFB) but were higher at 150 DAFB. Additionally, the contents of six polysaccharides in the exocarp of ‘Xiusu’ were higher than those in ‘Dangshansuli’ at 75 DAFB, the stage at which ‘Xiusu’ becomes russet in color, as well as at 150 DAFB; however, this was not observed for xylose. The contents of type I and II amino acids in the exocarp of ‘Xiusu’ were higher than those in ‘Dangshansuli’ at different stages, except for at 150 DAFB. The entire sequences of eight genes involved in the shikimate pathway and cell wall structure were cloned, and expression of these genes in the exocarp of ‘Dangshansuli’ and ‘Xiusu’ were significantly different during fruit development, indicating that these genes might be involved in the russeting process. It is speculated that the shikimate pathway connects primary and secondary metabolism and that high contents of sugars as carbon sources provide precursors for suberin, lignin and lignan to generate russet skin in pear.