GENETIC IMPROVEMENT AND EVALUATION OF HARD WINTER AND SPRING WHEATS
Location: Grain, Forage & Bioenergy Research
Title: A novel codominant marker for selection of the null Wx-B1 allele in wheat breeding programs
| Saito, Mika - NIPPON FLOUR MILLS |
| Vrinten, Patricia - BIORIGINAL FOOD |
| Ishikawa, Goro - TOHOKU NATIONAL |
| Nakamura, Toshiki - TOHOKU NATIONAL |
Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 29, 2008
Publication Date: October 23, 2008
Citation: Saito, M., Vrinten, P., Ishikawa, G., Graybosch, R.A., Nakamura, T. 2008. A novel codominant marker for selection of the null Wx-B1 allele in wheat breeding programs. Molecular Breeding 23:209-217 (2009).
Interpretive Summary: Over the past decade, wheat breeders have been working to develop wheats with altered starch properties. Altering the starch properties leads to altered cooking properties, and, hopefully, expanded use of wheat starch in the food processing and starch industries. The most commonly sought modification is the development of amylose-free, or waxy starch. Such starch is composed only of amylopectin, a complex biopolymer formed of both straight and branched chains of glucose. To produce such wheats, breeders have been relying on the deployment of natural, non-GMO approaches. Such approaches entail the use of spontaneous mutations in genes encoding various forms of an enzyme necessary for amylose synthesis. If this enzyme is lacking, starch still is formed, but it is composed only of amylopectin. Breeding such wheats is difficult, as the three necessary mutations all are recessive, meaning they are masked by the presence of a normal gene in the heterozygous condition. Heterozygotes carry one normal and one mutant gene. To facilitate the introgression of the mutant gene, the authors developed a DNA-based method for its detection. The method allows the detection of lines carrying one mutant gene, even when a normal functional gene still is present. Application of this DNA marker will reduce by 50% the number of years necessary to introgress the mutant genes into adapted genetic backgrounds.
Waxy protein (granule-bound starch synthase I) is a key enzyme in the synthesis of amylose in endosperm tissue. The amylose content of wheat flour plays a significant role in determining Japanese udon noodle quality. Most wheat cultivars suitable for producing udon noodles have a low amylose level due to a lack of Wx-B1 protein conditioned by null Wx-B1 alleles. It was previously determined that the entire coding region of the wheat Wx-B1 gene is deleted in the most common null allele. However, the extent and breakpoints of the deletion have not been established. In this study, the position of the 3’ deletion breakpoint was refined by mapping with PCR-based markers. Using information from this analysis, a chromosome walk was initiated and the DNA sequence flanking the deletion breakpoints was obtained. The deletion included a 3872 bp region downstream from the termination codon of Wx-B1 gene. Based on similarity with T. monococcum sequences, it was estimated that approximately 60 kb upstream of the Wx-B1 gene was also deleted. Using this sequence information, a codominant marker for the identification of the Wx-B1 null allele was developed. This marker can unambiguously identify heterozygous plants, which will accelerate the selection of partial waxy mutants carrying the Wx-B1 null allele.