| Wheat (Triticum aestivum L.) is one of the most important staple crop in the world. Drought stress is a major environment constraint greatly impacting wheat production. It is a fundamental approach to mining drought tolerance gene resources for new variety breeding. Wheat germplasm is very abundunt in China and there are lots of functional genetic variations for drought tolerance. Identifying these functionally alleles contributes to understanding molecular mechanism for drought tolerance, and developing functional markers based on these alleles, thus improving drought tolerance of wheat new germplasm and hybrids by marker-assisted selection. Association analysis is a powerful way to identify functional alleles associated with phenotype.Structural subunit gene TaPP2Aa and catalytic subunit gene TaPP2Ac of protein phosphatase 2A (PP2A) involved in abiotic stress, such as drought, high salt, low temperature and exogenous ABA in wheat. We choose natural population consist of 154 wheat germplasm,4 genetic mapping population, wild relative species and nulli-tetrasomic lines of Chinese spring, in order to analyze sequence diversity and gene location of different genome in TaPP2Aa/c, two candidate genes for drought tolerence. Developing functional markers and mapping TaPP2Aalc. In addition, field phenotypes and seedling biomass related to drought tolerance were characterized for natural population consist of 154 wheat germplasm. Finally, association analysis between TaPP2Aalc polymorphisms with phenotype variations were performed in order to identify functional alleles and haplotype that are responsible to drought tolerance phenotype variations.1. Nucleotide diversity (π) in A, B and D genome of entire TaPP2Aa region were 0.00062,0.00227 and 0.00037. Nucleotide diversity (π) in A, B and D genome of entire TaPP2Aa region were 0.00074,0.00962 and 0.00050. It is similar in these two genes and demonstrate that there are high nucleotide diversity in B genome of wheat, but D genome is most conservation in the three genone of wheat.2. The TaPP2Aa gene was located on chromosomes 5A,5B and 5D. TaPP2Aa-B was mapped in the intervals between markers Xwg909 and Xgwm67 on chromosome 5B in RIL population(Opata 85×W7984),4.0 cM and 3.6 cM from the flanking markers, and between markers Xgwm234 and WMC363 on chromosome 5B in DH population(Hanxuan 10 hao×Lumai 14),7.5 cM from WMC363,3.6 cM and 11.4 cM from the common marker Xgwm67 in two populations, respectively. TaPP2Aa-D was mapped in the interval between markers Xcmwg770 and Xbarc205 on chromosome 5D in RIL population(Opata 85×W7984),9.8 cM and 10.0 cM from them. Through comparative analysis with main effect QTLs for stress resistance in DH and RIL genetic populations, the genetic linkage between TaPP2Aa and stress-resistant QTLs was identified.3. TaPP2Ac-A was mapped next to markers WMC173 on chromosome 4A in DH(Lovrin 10×Chinese spring),4.4 cM from the flanking marker. TaPP2Ac-B was mapped in the intervals between markers KSUM154 and WMC47 on chromosome 4B in RIL population(Yanzhan 1 haoxZaosui 30),3.7 cM and 23.5 cM from the flanking marker. Through comparative analysis with QTLs in DH and RIL genetic populations, the genetic linkage between TaPP2Ac and thousand grain weight QTLs was identified.4. Four haplotype of TaPP2Aa-B associated with plant height (PH), length from flag leaf pulvinus to spike base (LFS), peduncle length (PLE) and seeding biomass(SBM). Hap-B1 had a significantly positive effect on drought tolerance and its drought resistance index (DRI) was higher than other haplotype. Hap-A and Hap-G of TaPP2Ac-A associated with thousand grain weight and drought resistance index (DRI) of it and spike number per plant(SNP). Hap-A had more significantly positive effect on thousand grain weight and drought resistance index (DRI) than Hap-G. Hap-4093 and Hap-4044 of TaPP2Ac-B associated with plant height (PH), peduncle length (PLE) and drought resistance index (DRI) of them.The drought resistance index (DRI) of Hap-4093 was higher than Hap-4044. |
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