Isolation and Expression Analysis of Anthocyanin Biosynthesis Genes from the Red Chinese Sand Pear, Pyrus pyrifolia Nakai cv. Mantianhong, in Response to Methyl Jasmonate Treatment and UV-B/VIS Conditions

Abstract

The effects of UV-B/VIS on the expression of genes involved in anthocyanin biosynthesis in the red Chinese sand pear cultivar ‘Mantianhong’, and the role played by the plant hormone methyl jasmonate (MJ) in this effect, were investigated. Four full-length cDNAs and three partial cDNA fragments of genes involved in anthocyanin biosynthesis were isolated from the cultivar. PpPAL2 and PpCHS2 showed considerable sequence identity to the reported PpPAL1 and PpCHS1 sequences. Other genes showed low pronounced sequence identity to other reported members of the same gene family. Bagged mature pear fruits were harvested and then used for postharvest treatment. Fruits were immersed in distilled water, then irradiated with UV-B/VIS light; or treated with MJ first, and then irradiated with UV-B/VIS light. Fruits immersed in distilled water and kept in darkness were used as controls. During UV-B/VIS irradiation, most anthocyanin biosynthesis genes were upregulated in pears in quantities commensurate with the accumulation of anthocyanin, but PpDFR1, PpDFR2, PpbHLH, and PpWD40 were not. MJ treatment had two effects on the expression of genes related to anthocyanin biosynthesis. It advanced the peak time and increased mRNA levels. Each family member of genes involved in anthocyanin biosynthesis showed a differential expression profile. The expression patterns of two genes regulating MJ-mediated plant responses, PpJAZ1 and PpCOI1, were also analyzed. More obvious downregulation and upregulation of PpJAZ1 and PpCOI1, respectively, were detected at 2 days of irradiation (DI) in fruits that were subjected to MJ treatment, as the expressions of most genes related to anthocyanin biosynthesis peaked at this time. We also showed that the regulation of MJ and UV-B/VIS occurred at the transcriptional level. These findings should improve our understanding of the molecular mechanism(s) underlying anthocyanin biosynthesis, which may in turn facilitate the development of new methods to improve fruit color.