Isolation, Identification And Functional Marker Development Of Wheat TaTGW6 Genes

The phytohormone auxin is an important enzyme that regulates almost all functions of plant growth and development. The most common and important naturally occurring auxin is indole-3-acetic acid （IAA）. The TGW6 gene encodes a novel indole-3-acetic acid-glucose hydrolase and plays a significant role in improving thousand grain weight （TGW） and yield by accumulation of carbohydrates in rice grains. In the current study, nine TGW6 orthologs including three from bread wheat chromosomes group 2, three orthologs from chromosome group 7 and three orthologues from chromosome group 3 were isolated using genome specific primers. These orthologues were designated as TaTGW6-2A, TaTGW6-2B and TaTGW6-2D from group 2 chromosomes and TaTGW6-7A, TaTGW6-7B and TaTGW6-7D from group 7 chromosomes. Sequence and alignment analysis expressed that cloned sequences consists of 942-,942-and 922-bp fragments from wheat chromosomes 2AL,2BL and 2DL, respectively. Whereas the cloned sequences from wheat chromosomes 7A, 7B and 7D consists of 972-,947-and 844-bp fragments respectively. Open reading frame （ORF） prediction and alignment analysis indicated that the cloned sequences have single exons without introns and high similarity with OsTGW6 （about 60% in amino acid）. Unfortunately, no polymorphism was observed in the orthologues from 2 and 7 chromosomes between individuals of the two contrasting sets of cultivars for TGW. The orthologues from 3 chromosomes were designated as TaTGW-Al, TaTGW6-B1 and TaTGW6-D1, respectively. TaTGW6-B1 and TaTGW6-Dl are lost-of-function, whereas TaTGW6-Al harbors three single-nucleotide polymorphisms （SNPs） between cultivars with higher and lower TGW, forming two haplotypes, TaTGW6-Ala and TaTGW6-Alb. A derived cleaved amplified polymorphic sequence marker, TaTGW6-Al-CAPS, was developed to differentiate the two haplotypes. Linkage analysis using the wheat 90K iSelect SNP array mapped TaTGW6-Al-CAPS at 18cM from BobWhite_c47304₅6 in a RIL population derived from Zhou 8425B/Chinese Spring. A QTL for yield at the TaTGW6-Al locus explained 17.4% of the phenotypic variance in average yield over four environments. Association analysis on 242 Chinese and foreign cultivars indicated that TaTGW6-Al was significantly associated with TGW. The cumulative frequency of the TaTGW6-Ala allele associated with higher TGW was approximately 80%, indicating that the TaTGW6-Ala allele was positively selected in wheat breeding. In conclusion, TaTGW6-Al in conjunction with its molecular marker may contribute as a valuable gene in improving yield potential in wheat.