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Title: Genetic Characterization of Kernel Polyphenol Oxidases in Wheat and Related Species

item Beecher, Brian
item Xu, Steven

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2007
Publication Date: 8/19/2008
Citation: Fuerst, E., Beecher, B.S., Xu, S.S. 2008. Genetic Characterization of Kernel Polyphenol Oxidases in Wheat and Related Species. Journal of Cereal Science 48:359-368.

Interpretive Summary: An undesired brown color appears in Asian noodle and certain other wheat products due to the activity of an enzyme known as Polyphenol Oxidase (PPO). Improvements have been made in wheat cultivar fields that are aiding in eliminating the brown coloring from affected wheat products, but further improvements could be made by identifying how and which wheat relatives have less PPO activity and using that knowledge in wheat cultivation to produce wheat with low PPO activity. In this study, certain aspects of PPO genetics and activity were explored in order to gain further knowledge of the origins of PPO and the levels of PPO that occur in various wheat relatives. The results of the study show that high PPO activity is likely caused by only a small number of the many PPO genes that are found in wheat and that a single genetic locus on a specific chromosone is possibly the cause of high PPO activity.

Technical Abstract: Polyphenol oxidase (PPO) activity causes undesirable darkening of raw Asian noodles and other wheat products. In this study we investigate the genetic origins and diversity of wheat kernel PPO. PPO was characterized via activity assays, antigenic staining, and Southern blots in Triticum aestivum, T. dicoccooides, T. durum, T. dicoccum, T. monococcum, T. urartu, Aegilops speltoides, and Ae. tauschii. Among these species, PPO activity was well correlated with antigenic staining intensity toward a wheat kernel-type PPO antibody. High PPO activity was observed in all three T. monococcum accessions (Am genome), one Ae. speltoides accession, one T. durum accession, and two hexaploid wheat cultivars. Southern blots suggested the presence of two or more kernel-type PPO genes in diploid progenitors of the hexaploid A, B, and D genomes. Whole-kernel PPO activity was evaluated in disomic substitution lines derived from three T. dicoccoides accessions in the background of T. durum 'Langdon'. PPO activity was primarily associated with chromosome 2A and to a much lower degree with chromosome 2B. DNA sequence comparisons showed that the intron associated with the high PPO allele on chromosome 2AL of hexaploid wheat had 94% nucleotide identity with the homeologous intron found in T. monococcum, a species with high kernel PPO activity. This implies that the ancestral PPO allele on the A genome is one of high activity, and the low PPO allele found in hexaploid wheat represents a relatively recent genetic alteration. Results confirm the presence of multiple kernel-type PPO genes in the diploid and tetraploid progenitors and relatives of hexaploid wheat. However, it is likely that relatively few of the many kernel-type PPO genes present in wheat contribute substantially to kernel PPO activity. A single genetic locus on homeologous group 2 chromosomes may be the primary cause of high PPO activity in wheat kernels.