In-depth genetic analysis reveals conditioning of polyphenol oxidase activity in wheat grains by cis regulation of TaPPO2A-1 expression level.

Time-dependent darkening and discoloration of wheat product caused by high polyphenol oxidase enzymes (PPO) activity is the most undesirable character in wheat processing industry. We performed GWAS of PPO activity in wheat grains utilizing an association panel and identified 22 significant SNPs. The most significant GWAS peak on chromosome 2A was verified by QTL analysis of PPO activity. The candidate gene for this GWAS peak was identified as TaPPO2A-1, which was the highest expressed PPO gene in wheat grains. The expression level of TaPPO2A-1 was significantly correlated with PPO activity. The most significant association signal for GWAS of the expression values of TaPPO2A-1 pinpointed to the genomic region containing TaPPO2A-1. The results suggested that cis regulation of TaPPO2A-1 expression is the key factor in regulation of PPO activity in wheat grains. The conclusion was further enhanced by haplotype analysis of seven SNPs in the promoter of TaPPO2A-1.