| Pre-harvest sprouting (PHS) of wheat is a international balefulness which reduces the quality and economic value of the grains. Breeding for PHS tolerant cultivars is important in the Northern and Northeastern as well as in the Yangtze River valley region in China. So improvement of PHS tolerance is one of the most important objectives in wheat breeding. In this study, Vp-1 and Vp-1's allelic varieties had been isolated from different PHS tolerance cultivars, and the expression characterization of the Vp-1 gene was studied by Semi-quantitative RT-PCR. According to the sequence and expression characterization of the Vp-1, a STS marker had been developed and validated, the efficiency was assessed with other three PHS markers and had been used in molecular assisted- selecting. The main details of the result as follows:1. Two new Viviparous-1 allelic variants related to PHS tolerance were identified on chromosome 3B of bread wheat, and designated as Vp-1Bb and Vp-1Bc, respectively. Sequence analysis showed that Vp-1Bb and Vp-1Bc had an insertion of 193-bp and a deletion of 83-bp fragment, respectively, which were begot to retrotransposon and transposon. A co-dominant STS marker of Vp-1B gene covering the insertion and deletion region was developed and designated as Vp1B3. Statistical analysis indicated that Vp1B3 was strongly associated with PHS tolerance suggesting that Vp1B3 could be used as an efficient and reliable co-dominant marker in the evaluation of wheat germplasm for PHS tolerance and marker-assisted breeding for PHS tolerant cultivars.2. Semi-quantitative RT-PCR analysis showed that alternatively spliced transcripts of the Vp-1A, Vp-1B and Vp-1D homologues were present and there were no differences in the splicing patterns or abundances of Vp-1A and Vp-1D from 25, 30 and 35 DAP embryos between PHS-tolerant and susceptible cultivars. The protein was expressed more highly in genotypes with Vp-1Bb and Vp-1Bc than in those with Vp-1Ba. Furthermore, genotypes with different levels of tolerance to PHS showed different responsiveness to ABA exposure and differences in transcript levels of Vp-1Ba, Vp-1Bb and Vp-1Bc were observed after ABA treatment. The results indicated that insertion or deletion in the third intron region may affect the expression of the Vp-1B gene and its sensitivity to ABA, and thus its resistance to PHS. 3. Another three PHS tolerance-associated markers: MST101, wmc104 and Xgwm155, as well as Vp1B3, were employed, aimed at assessing the efficiency of these markers in selecting genotypes with higher PHS tolerance. Variations at Vp1B3 and Xgwm155 were associated with PHS response, but not for STS marker MST101 and STMS marker wmc104, and the selection efficiency would be improved by use of both markers together.4. Three methods, i.e., spike germination rate (SGR), germination index (GI), and molecular marker Vp1B3, were used to screen the PHS tolerance of 33 new wheat lines. The red grain PHS resistance line CA0489 possessed both Vp1Bb tolerance gene and red grain related dormancy gene; red grain PHS resistance line CA0481 had Vp1Bc tolerance gene. The two white grain PHS resistance lines CA0509 and CA0459 did not contain Vp1 tolerance gene, their PHS tolerance might be related to the characters of spike and the stayers excreted from glumes.5. In addition, 38 landraces,94 historical cultivars and 106 modern cultivars were used to evaluate the diversity of the Vp-1B gene associated with PHS tolerance. Four alleles were found in the wheat varieties tested. Frequencies of Vp1Ba alleles, Vp1Bb, Vp1Bc and Vp1Be genotypes were 45%, 18%, 34% and 3%, respectively, in landraces; 30%, 10%, 60% and 0%, respectively, in historical wheat; while 31%, 1%, 68% and 0%, respectively, and no Vp-1Bd genotype in studied 238 cultivars, which presented in Europe wheat cultivars, was found in this study.
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