Functional Identification Of TaGW2-6A And QTL Analysis For Kernel Weight Related Traits

Thousand kernel weight (TKW), kernel number per spike and spike number per unit areaare three major determinants of wheat grian yield and the improvement of kernel weight isone of the important ways to increase the wheat yield. Kernel length (KL) and kernel width(KW) are important factors that affect the grain size, and have great effects on grain weight.TKW, KW and KL are quantitative traits controlled by many genes with small effects andvulnerable to environmental impacts, so the development and application of functionalmarkers may facilitate rapid identification of grain weight genes and lead to more efficientwheat breeding. In addition, the study on the relation between TKW and kernel size traits(KW, KL) and dissection of the genetic mechanism of the effect of KW and KL on TKW onthe level of QTL is of great significance to the improvement of wheat yield. In the presentstudy, three populations (one BC2F4, one RIL population and one natural population) wereused to identify the function of wheat grain gene TaGW2-6A and the relationship between thetwo allelic variations (Hap-6A-A/G) and kernel weight related traits (TKW, KW and KL). Inaddition, the unconditional and conditional QTL for kernel weight related traits wasperformed using three genetic populations (one DH population and two RIL populations). Theresults were as following:1、Three populations were used to vertify the function of the two allelic variations ofTaGW2-6A (Hap-6A-A/G). The results indicated the differences in average thousand grainweight, width, and length between haplotypes Hap-6A-G and Hap-6A-A were8.09g,0.22mm, and0.38mm, respectively, in the BC2F4population;4.01g,0.11mm, and0.10mm inthe RIL1population; and3.95g,0.10mm, and0.20mm in the natural population. All thedifferences were significant. Sequencing results of the products of second round PCRindicated that a167bp TaqI restriction fragment had been generated from small-grain-sizematerials because of three TaqI restriction sites (TCGA). However, the large-grain-sizevariant generated a218bp fragment due to a single-nucleotide mutation (SNP)(TCGA�'TCGG) at the third site. TaGW2-6A expression levels were negative with respect tograin width, length, and weight. For this reason, Hap-6A-G was considered a superior allele. These results contradict those of a previous study, which showed Hap-6A-A to besignificantly associated with wider grain and higher grain weight.2、14and11additive QTL for KW and KL were detected in three genetic populations. Of14QTL for KW, Qkw1B detected in the RIL2population had the greatest contribution andexplained15.24%of phenotypic variance indicating it was a major QTL for KW. Of11QTLfor KL, Qkl6D identified in the DH population had the greatest contribution and accounted for10.18%of phenotypic variance indicating it was a major QTL for KL. In addition,7and10pairs of epistases for KW and KL were detected in three genetic populations. Of7pair ofepistatic effects for KW, Qkw7A/Qkw7D detected in the DH population possessed the greatestcontribution and contributed8.32%of KW variance. Of10pair of epistatic effects for KL,Qkl2A-2/Qkl3B.1identified in the RIL1population accounted for the largest KL variance andits contribution was25.53%.3、Both unconditional and conditional mapping methods were applied in the analysis ofgenetic relationship between TKW and kernel size traits (KW and KL).36unconditional andconditional additive QTL for TKW and30pair of unconditional and conditional epistaticeffects for TKW were detected in three genetic populations. Both KW and KL played animportant role in the heredity of TKW, while the contribution of KW was greater. The resultsshowed that both additive effects and epistases made significant contribution to the heredityof TKW. In addition, the conditional analysis method could indeed deeply dissect the geneticrelationship among kernel weight related traits (TKW, KW and KL). For example, in the RIL2population, three additive QTL were found to be completely dependent of KW, butindependent of KL, Qtkw1A.1, Qtkw2A-1and Qtkw7A, respectively. This indicated that theseQTL were important in wheat breeding because they could increase TKW by regulating KWwithout affecting KL.4、In the present study, some pleiotropic chromosome regions simultaneously controllingKW, KL and TKW were identified. The additive QTL—Qkw3A controlling KW was detectedin the chromosome region Xswes107-Xbarc86on3A of the DH population, and this regionsimultaneously participate in the epistatic effect (Qtkw3A-2/Qtkw5B.1) for TKW. Theadditive QTL for KW and TKW (Qkw6A and Qtkw6A-1) were both detected in the chromosome interval Xgwm82-Xwmc553on6A of the DH population. In the RIL1population, the QTL for KW and TKW (Qkw6A.1and Qtkw6A.1) were both located in theinterval CFE043-TaGW2-CAPS on the chromosome6A, and the positive alleles were bothcontributed by the female parent Shannong01-35. In the RIL2population, Qkl2B andQtkw2B-1which were the additive QTL for KL and TKW were both located in thechromosome region wPt-0473-wPt-1068on2B. The marker interval wPt-7524-wPt-2788onchromosome4A contained the additive QTL for KW, KL and TKW (Qkw4A、Qkl4A-1andQtkw4A-1), while the additive QTL for KW and KL (Qkw6A.3、Qkl6A.3) were detected in theinterval wPt-730772-Xgpw312on chromosome6A at the same time. It was possible thatthese chromosome regions containing pleiotropic or closely linked QTL greatly contributed tothe wheat grain yield formation.