Inheritance And Gene Mapping Of Branched Spikelets In Wheat

Wheat(Triticum aestivum L.)spike architecture is an important trait associated with spike development.Here,we report a naturally occurring wheat mutant(BSL1)with branched spikelets from its wild-type YD-16,which has a normal spike trait and confers a moderate level of resistance to wheat Fusarium head blight(FHB).The lateral meristems positioned at the basal parts of the rachis node of the BSL1 mutant develop into ramified spikelets characterized as multiple spikelets.The BSL1 mutant shows three to four-day longer growth period but less 1000-grain weight than the wild type,and it becomes highly susceptible to FHB infection,indicating that the locus controlling the BSL trait may have undergone an intensively artificial and/or natural selection in modern breeding process.The self-pollinated descendants of the lines with the BSL trait consistently segregated with an equal ratio of branched and normal spikelets(NSL)wheat,and homozygotes with the BSL trait could not be achieved even after nine cycles of self-pollination.Distinct segregation patterns both from the self-pollinated progenies of the BSL plants and from the reciprocal crosses between the BSL plants with their sister NSL plants suggested that gametophytic male sterility was probably associated with the heterozygosity for the BSL trait.The orthogonal crosses combinations were arranged with BSL1 and Wheaton,and all F1 plants had NSL.The offspring of F1 and F2 were NSL plant when BSL1 as male parents,but the offspring of F2 showed the separation of spike architecture when BSL1 as female parents.This phenomenon further indicated that the early abortion of male gametes was responsible for branched spikelets development.According to the separation ratio,we speculated that the phenotype of the mutant was controlled by polygenes,one of which was heterozygous.After that,we analyzed the 55K SNP chip results of part BSL plants and NSL plants in the F2 and F3 generation when BSL1 as female parents.We found that SNPs on chromosome 2A and 2D were significantly correlated to BSL trait.Phenotyping and genotyping of F3 population indicated that the gene controlling BSL trait on chromosome 2A(TaBSL.2A)was located between molecular markers y120 and 4066,with genetic distance of 2.6cM and physical distance of about 14Mb.Then,297 recombinants were obtained by screening more than 8000 single plants of F4 secondary population.The gene(TaBSL.2A)was further located between the molecular markers M765 and M766,with a physical distance of about 2Mb.Transcriptome sequencing of the RNA bulks contrasting in the two types of spike trait at the heading stage indicated that the differentially expressed genes(DEGs)on chromosome 2DS may be critical for the BSL trait formation.Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis showed that carbohydrate metabolism may be involved in the BSL trait expression.This work provides valuable clues into understanding development and domestication of wheat spike as well as the association of the BSL trait with FHB susceptibility.