Title : Identification and fine-mapping of a major QTL qSB.A09 that controls shoot branching in Brassica rapa ssp. chinensis Makino
Abstract:
hoot branching is a complex quantitative trait that contributes to plant architecture and ultimately yield, yet the genetic control of shoot branching in Brassica rapa L. subsp. chinensis remains poorly understood. In this study, a major QTL for shoot branching, designated shoot branching 9 (qSB.A09), was detected on the long arm of chromosome A09 in Brassica rapa L. subsp. chinensis using bulked segregant analysis (BSA) of an F2 population. Traditional QTL mapping of the F2 population was also carried out, revealing six QTLs in different regions. Of these, the mapping region on chromosome A09 was consistent with the results of BSA-seq analysis as well as being stable over the 2-year study period, contributing to 19.37 and 22.18% of the phenotypic variation across multiple genetic backgrounds. Using extreme recombinants, qSB.A09 was further delimited to a 127-kb genomic region harboring 28 annotated genes. The GRAS transcript factor Bra007056, an ortholog of MONOCULM 1 (MOC1), which is the key gene controlling tillering in rice, was subsequently identified as a potential candidate gene. Quantitative RT-PCR further revealed that expression of Bra007056 was positively correlated with the shoot branching phenotype. Furthermore, an Indel marker specific to Bra007056 co-segregated with the shoot branching trait in the F2 populations. Overall, these results provide a foundation for uncovering the molecular mechanism of shoot branching in Brassica rapa ssp. chinensis Makino Keywords: Non-heading Chinese cabbage, shoot branching, QTL, fine mapping, candidate gene
