QTL Mapping For Seminal Root Number In Synthetic Hexapliod Wheats And Molecular Characterization Of TaMYBX

Root is one of the main organs of plants,which is the main channel of grains to absorb water and nutrient.The root system architecture(RSA)affects wheat yield as well as the time and range of water uptake from the soil.The number of seminal roots is the main factor affecting RSA at seedling stage.In this paper,the WinRHIZO was used to count the number(three replicates)of seminal root in the recombinant inbred lines(HAI-120)that gained by crossing synthetic wheat(SHW-L1)and common wheat Chuanmai 32(CM32).Combined with the genetic map that was constructed by wheat 660 k SNP assay,a total of six QTLs on chromosomes 1B,3A,6A,6B and 6D were detected,named QRN.sicau-1B,QRN.sicau-3A,QRN.sicau-6A,QRN.sicau-6B.1-2,QRN.sicau-6D respectively.The phenotypic variation explained by each of these QTLs ranges from 10.2 to 15.8%.Among them,one of major QTL,QRN.sicau-1B explained 15.8% of phenotypic variation.Combined with RNA-seq data,the candidate gene TaMYBX was found at a distance of 12.6 Mb from the QRN.sicau-1B locus,which was specifically expressed in SHW-L1.TaMYBX is 3697 bp in length and has 3 exons and 2 introns,encoding a R2R3 type MYB transcription factor.Phylogenetic analysis revealed that this gene was specific on chromosome 1B and has three copies derived from the tetraploid wheat(Triticum turgidum ssp.dicoccoides).There was no difference in the coding sequence of this gene between SHW-L1 and CM32,but real-time quantitative PCR analysis showed that this gene mainly expressed in the root tip of SHW-L1 at the stage of 48h~7D after germination.This gene may be related to the number of seminal roots.In addition,two copies of this gene were located in the region of PHS.sicau-1B,a major QTL related to pre-harvest sprouting(PHS),but TaMYBX was not the candidate gene of PHS.sicau-1B.