Genetic characterization and expression analysis of wheat (Triticum aestivum) line 07OR1074 exhibiting very low polyphenol oxidase (PPO) activity

Authors: HYSTAD, S. - Montana State University; MARTIN, J. - Montana State University; Graybosch, Robert; GIROUS, M. - Montana State University

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2015
Publication Date: 5/16/2015
Publication URL: http://www.springer.com/home?SGWID=0-0-1003-0-0&aqId=2844978&download=1&checkval=458ec754032e3b28d1e16b563d1850ba http://www.springer.com/home?SGWID=0-0-1003-0-0&aqId=2844978&download=1&checkval=458ec754032e3b28d1e16b563d1850ba
Citation: Hystad, S.M., Martin, J.M., Graybosch, R.A., Girous, M.J. 2015. Genetic characterization and expression analysis of wheat (Triticum aestivum) line 07OR1074 exhibiting very low polyphenol oxidase (PPO) activity. Journal of Theoretical and Applied Genetics. Volume 128, Issue 8 (2015), Page 1605-1615.

Interpretive Summary: Discoloration is a common source of waste in food products, and leads to excessive amounts of potentially needed calories being discarded each year. Many discoloring reactions are the result of activities of enzymes known as polyphenol oxidases. Such enzymes are responsible for well-known undesirable reactions such as browning of sliced apples and avocados. Polyphenol oxidases also cause discoloration in products of wheat, including fresh noodles, fresh and frozen breads, and refrigerated biscuits. Hard white winter wheats are desired, both for domestic production of whole grain breads, and for export markets. Asian markets would purchase additional U.S. hard white winter wheat if such wheats had reduced, or absent, levels of grain polyphenol oxidase. While some low polyphenol oxidase wheats have been developed, complete removal of the enzyme would be even more desirable. In this paper, naturally occurring genetic mutations were characterized. These mutations result in nearly complete loss of polyphenol oxidase activity. The mutations were discovered in a wheat breeding line 07OR1074, developed by controlled matings of two Australian wheats dating to the 1930’s, and maintained by the USDA-ARS National Small Grains Collection. The trait is inherited and expressed in improved breeding lines developed by crossing 07OR1074 with elite Montana wheats. Further introgression of this trait into elite lines will result in highly desirable cultivars that will expand the demand for U.S. hard white winter wheat. In addition, the study demonstrates the continued importance of the USDA-ARS germplasm collections in the maintenance of key genetic resources for American farmers.

Technical Abstract: Wheat (Triticum aestivum) polyphenol oxidase (PPO) contributes to the time dependent discoloration of Asian noodles. Wheat contains multiple paralogous and orthologous PPO genes , Ppo-A1, Ppo-D1, Ppo-A2, Ppo-D2, and Ppo-B2, 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. 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 cultivars Choteau and Vida. Expression analysis using RNA-seq demonstrated no detectable Ppo-A1 transcripts in 07OR1074 while Ppo-D1 transcripts were present at less than 10% of that seen in 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 segregating populations. Evaluation of lines indicated a substantial genotypic effect on PPO with Ppo-A1 and Ppo-D1 alleles contributing significantly to total PPO in both populations. These results show that the novel mutations in Ppo-A1 and Ppo-D1 present in 07OR1074 are both important to lowering overall wheat seed PPO activity and may be useful to produce more desirable and marketable wheat based products.