Isolation of a cinnamoyl CoA reductase gene involved in formation of stone cells in pear (Pyrus pyrifolia)

Stone cell which appears in most pear cultivars contributes badly to pear internal quality. Lignin is the important component of stone cells and its first biosynthetic but specific step is catalyzed by cinnamoyl CoA reductase (CCR). In the present study, a cDNA encoding CCR, named as PpCCR (GenBank accession no. GU138672), was isolated from pear (Pyrus pyrifolia) fruit. Its full length is 1,247 bp with a putative maximal open reading frame of 1,017 bp, encoding a protein of 339 amino acids. Sequence alignment revealed that the deduced protein contained a typical CCR catalytic site and NADP(H) binding site. Phylogenetic analysis showed that PpCCR belonged to dicot CCR class II in which most CCRs participated in the regulation of lignin biosynthesis. PpCCR transcript could be detected in leaves, flowers and fruits. In addition, PpCCR expression profiles during fruit development were compared between two cultivars with significant difference in stone cell content in the flesh. Although PpCCR expressed in a similar pattern between the two cultivars and their transcript level consisted strictly with the change of lignin content, its transcript level was always higher in the high-lignin content cultivar than in the low-lignin content cultivar during fruit development. Therefore, it could be suggested that PpCCR is involved in the regulation of lignin biosynthesis and plays an important role in stone cell formation in pear flesh.