Molecular Characterization Of Photoperiod And Quality Genes In Chinese Wheat Cultivars

Imcreasing the adaptability and the end processing quality of wheat are an important breeding goal in China. Ppd-D1a is photoperiod insensitive gene at Ppd-D1 locus on common wheat chromosome 2D and is closely associated with wide adaptability.Yellow pigment (YP) content is responsible for flour color. A bright white to creamy colour is preferred for white Chinese noodles and steamed bread in China, requiring a low YP content in wheat grains.Wheat HMW-GS and LMW-GS have a high correlation with dough strength that determines bread-making quality. Studying above characters using molecular makers can not only understand the distribution of genes for the related traits and screen good materials with desirable alleles; also help know adaptive mechanism in different wheat growing regions in China and converge good genes controlling different characteristic into only one genotype. Distribution of photoperiod insensitive gene Ppd-D1a was detected using allele-specific marker in a total of 926 Chinese wheat landraces and improved cultivars collected from nine wheat growing zones and origin of Ppd-D1a was deduced from molecular level in combination with pedigree analysis. Distributing frequency of phytoene synthease gene for yellow pigment content on chromosome 7A (Psy-A1) was studied with molecular marker YP7A in 374 improved cultivars from 4 winter wheat growing regions and 197 core landraces in China; the association was validated between YP content and Psy-A1 alleles and good cultivars with Psy-A1b for low yellow pigment content were screened. A total of 224 and 216 cultivars from 4 winter wheat zones were tested for HMW-GS and LMW-GS subunits at Glu-B3 locus, respectively, by allele-specific makers; frequencies of alleles detected and the availability of molecular markers were indicated. The main results in the present study were as follows:1. The molecular marker developed from Ppd-D1 gene sequence with highly specific characteristics and repeatability could discriminate the alleles Ppd-D1a and Ppd-D1b. The average frequency of the photoperiod-insensitive Ppd-D1a allele was 66.0%, with the frequencies of 38.6% and 90.6% in landraces and improved cultivars, respectively. However, the Ppd-D1a allele was present in all improved cultivars released after 1970s except for spring wheats in high latitude northwestern China, and winter wheats in Gansu and Xinjiang. The presence of the Ppd-D1a allele in landraces and improved cultivars increased gradually from north to south, illustrating the relationship between photoperiod response and environment. Ppd-D1a in Chinese wheats was derived from three sources, Japanese landrace Akagomughi and Chinese landraces Mazhamai and Youzimai.2. Characterization of phytoene synthease gene for yellow pigment (YP) content indicated that YP7A, a co-dominant marker of Psy-A1 gene, can amplify a 194-bp and a 231-bp fragment in the genotypes with Psy-A1a frequently for higher YP content and Psy-A1b mostly for lower YP content, respectively. Highly significant differences in YP content were detected between the genotypes with Psy-A1a and those with Psy-A1b (P<0.01). The occurrence frequencies for Psy-A1a and Psy-A1b were 66.8% and 33.2% in the 374 improved cultivars, respectively. Significant differences of allelic variations were found in improved wheat cultivars from different wheat regions of China. In the Northern Winter Wheat Region, Yellow & Huai Facultative Winter Wheat Region, Middle & Low Yangtze Valley Winter Wheat Region and Southwestern Winter Wheat Region, frequencies of the allele Psy-A1a were 73.8%,73.9%,25.9% and 46.7%, respectively. Whereas frequencies of the alleles Psy-A1a and Psy-A1b in Chinese landraces were 97.5% and 2.5%, respectively.3. Molecular markers can more accurately evaluate HMW-GS composition in comparison with SDS-PAGE. Distribution of detected subunits were quite different in 224 Chinese winter wheat cultivars and advanced lines tested. Of them, 55 cultivars carried Dx5 subunit with a frequency of 24.6%; whereas 80 cultivars(35.7%)produced specific band (527bp) for By8. 5.8% for Bx20 based on markers Mar and ZSBy9aF1/R3, and Bx14+By15 was present in only one genotype, followed by two cultivars with Bx13+By16 according to marker ZSBy9F2/R2. Four Genotypes (1.8%) had Bx6 and five cultivars (2.2%) contained Bx17. One hundred and six (47.3%) varieties had By9, detected by ZSBy9aF1/R3, yielding 663-bp and 708-bp PCR fragments. Compared with the results of SDS-PAGE, 5 genotypes for Dx5 subunit were different in the test with allele specific molecular marker, with a 90.9% of consistent results, followed by 88.9% for By8, 100% for Bx17 and Bx6, 97.2% for By9. The difference may be mainly due to incorrect identifications of proteins that are functionally distinct, but have the similar molecular weights and relative mobilities in the test with SDS-PAGE.4. 8 gene-specific markers with good repeatability could be used for marker-assisted selection in wheat breeding programs targeting for LMW-GS at Glu-B3 locus. A total of 216 Chinese winter wheat cultivars produced 8 allelic variations, out of them, 34 (15.7%) genotypes contained Glu-B3g, followed by 34 (15.7%) cultivars with Glu-B3d, 15 (6.9%) genotypes with Glu-B3b, 4 with Glu-B3e, 13 (6.0%) with Glu-B3f; 8 and 4 materials with Glu-B3h and Glu-B3i, respectively. Some differences were found between the results of SDS-PAGE and those of allele specific marker test. This was due to lower differentiation for LMW-GS subunits using SDS-PAGE .In this study, the distribution were clarified for photoperiod insensitive gene Ppd-D1a, phytone synthease gene for yellow pigment content and high- and low-molecular-weight subunits allelic variation. Meanwhile, the characteristics of high efficiency and reliability of tested markers were validated in evaluating related gene alleles. The research was extremely useful for new cultivars selection with high production, good quality and wide adaptability in wheat breeding programs.