Allelic variation of polyphenol oxidase (PPO) genes located on chromosomes 2A and 2D and development of functional markers for the PPO genes in common wheat |
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| Authors: | X Y He Z H He L P Zhang D J Sun C F Morris E P Fuerst X C Xia |
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| Institution: | (1) Institute of Crop Science, National Wheat Improvement Center/The National Key Facility for Crop Gene Resources and Genetic Improvement, Chinese Academy of Agricultural Sciences (CAAS), Zhongguancun South Street 12, Beijing, 100081, China;(2) International Maize and Wheat Improvement Center (CIMMYT) China Office, c/o CAAS, Zhongguancun South Street 12, Beijing, 100081, China;(3) Beijing Engineering and Technique Research Center of Hybrid Wheat, Beijing Academy of Agricultural and Forestry Sciences, Beijing, 100097, China;(4) College of Agronomy, Northwest Sci-Tech University of Agriculture and Forestry, Yangling, 712100, Shaanxi Province, China;(5) USDA-ARS Western Wheat Quality Laboratory, Washington State University, P.O. Box 646394, Pullman, WA 99164-6394, USA;(6) Department of Crop and Soil Sciences, Affiliated with the Western Wheat Quality Laboratory, Washington State University, Pullman, WA 99164-6394, USA |
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| Abstract: | Polyphenol oxidase (PPO) activity is highly related to the undesirable browning of wheat-based end products, especially Asian
noodles. Characterization of PPO genes and the development of their functional markers are of great importance for marker-assisted
selection in wheat breeding. In the present study, complete genomic DNA sequences of two PPO genes, one each located on chromosomes
2A and 2D and their allelic variants were characterized by means of in silico cloning and experimental validation. Sequences
were aligned at both DNA and protein levels. Two haplotypes on chromosome 2D showed 95.2% sequence identity at the DNA level,
indicating much more sequence diversity than those on chromosome 2A with 99.6% sequence identity. Both of the PPO genes on
chromosomes 2A and 2D contain an open reading frame (ORF) of 1,731 bp, encoding a PPO precursor peptide of 577 amino acids
with a predicted molecular mass of ∼64 kD. Two complementary dominant STS markers, PPO16 and PPO29, were developed based on the PPO gene haplotypes located on chromosome 2D; they amplify a 713-bp fragment in cultivars with
low PPO activity and a 490-bp fragment in those with high PPO activity, respectively. The two markers were mapped on chromosome
2DL using a doubled haploid population derived from the cross Zhongyou 9507/CA9632, and a set of nullisomic–tetrasomic lines
and ditelosomic line 2DS of Chinese Spring. QTL analysis indicated that the PPO gene co-segregated with the two STS markers
and was closely linked to SSR marker Xwmc41 on chromosome 2DL, explaining from 9.6 to 24.4% of the phenotypic variance for PPO activity across three environments. In
order to simultaneously detect PPO loci on chromosomes 2A and 2D, a multiplexed marker combination PPO33/PPO16 was developed and yielded distinguishable DNA patterns in a number of cultivars. The STS marker PPO33 for the PPO gene on chromosome 2A was developed from the same gene sequences as PPO18 that we reported previously, and can amplify a 481-bp and a 290-bp fragment from cultivars with low and high PPO activity,
respectively. A total of 217 Chinese wheat cultivars and advanced lines were used to validate the association between the
polymorphic fragments and grain PPO activity. The results showed that the marker combination PPO33/PPO16 is efficient and reliable for evaluating PPO activity and can be used in wheat breeding programs aimed for noodle and other
end product quality improvement. |
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