Genetic Characterization and Expression Analysis of Wheat (Triticum aestivum) Line 07OR1074 Exhibiting Very Low Polyphenol Oxidase (PPO) Activity.

Wheat (Triticum aestivum) polyphenol oxidase (PPO) contributes to the time dependent discoloration of Asian noodles. Wheat contains multiple paralogous and orthologous PPO genes expressed in wheat kernels, Ppo-A1, Ppo-D1, Ppo-A2, Ppo-D2, and Ppo-B2. To date, wheat noodle color improvement efforts have focused on breeding cultivars containing Ppo-D1 and Ppo-A1 alleles conferring reduced PPO activity. A major impediment to wheat quality improvement is a lack of additional PPO alleles conferring reduced kernel PPO. Thus, the discovery of novel low or null PPO alleles is critical to further reduce PPO and improve noodle color stability. In this study, a previously reported very low PPO line, 07OR1074, was found to contain a novel allele at Ppo-A2 and null alleles at Ppo-A1 and Ppo-D1 loci. To examine the impact of each mutation upon kernel PPO, populations were generated from crosses between 07OR1074 and the hard white spring wheat varieties Choteau and Vida. Novel markers specific for the Ppo-D1 and Ppo-A2 mutations discovered in 07OR1074 along with the Ppo-A1 STS marker were used to screen the segregating populations. Evaluation of segregating populations indicated a substantial genotypic effect on PPO with Ppo-A1 and Ppo-D1 loci contributing significantly (P <.001) to total PPO in both populations. Expression analysis using RNA-seq demonstrated there were no detectable Ppo-A1 transcripts while Ppo-D1transcripts were shown to be down regulated in 07OR1074 relative to Vida and Choteau. Analysis of the color profile of Chinese white salted noodles revealed that the very low PPO line 07OR1074, produced noodles that were brighter (greater L^*), more yellow (greater b^*) and more red (greater a^*) with time for both white and whole wheat white salted Chinese noodles. These results show that mutations in Ppo-A1 and Ppo-D1 are important to lowering overall wheat seed PPO activity to produce a more desirable and marketable fresh noodle product.