QTL mapping plus bulked segregant analysis revealed a major QTL for shoot branching in non-heading Chinese cabbage. The candidate gene was then identified using sequence alignment and expression analysis. Shoot branching is a complex quantitative trait that contributes to plant architecture and ultimately yield. Although many studies have examined branching in grain crops, the genetic control of shoot branching in vegetable crops such as Brassica rapa L. ssp. chinensis remains poorly understood. In this study, we used bulked segregant analysis (BSA) of an F2 population to detect a major quantitative trait locus (QTL) for shoot branching, designated shoot branching 9 (qSB.A09) on the long arm of chromosome A09 in Brassica rapa L. ssp. chinensis. In addition, traditional QTL mapping of the F2 population revealed 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, explaining 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. We subsequently identified the GRAS transcription factor gene Bra007056 as a potential candidate gene; Bra007056 is an ortholog of MONOCULM 1 (MOC1), the key gene that controls tillering in rice. Quantitative RT-PCR further revealed that expression of Bra007056 was positively correlated with the shoot branching phenotype. Furthermore, an insertion/deletion marker specific to Bra007056 co-segregated with the shoot branching trait in the F2 populations. Overall, these results provide the basis for elucidating the molecular mechanism of shoot branching in Brassica rapa ssp. chinensis Makino.

中文翻译：

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qSB.A09 的鉴定和精细定位，这是控制芸苔属植物枝条分枝的主要 QTL。中华牧野。

QTL作图加上大量分离分析揭示了不结球大白菜芽分枝的主要QTL。然后使用序列比对和表达分析鉴定候选基因。枝条分枝是一种复杂的数量性状，有助于植物结构和最终产量。尽管许多研究已经检查了粮食作物的分枝，但蔬菜作物（如 Brassica rapa L. ssp.）的枝条分枝的遗传控制。chinensis 仍然知之甚少。在这项研究中，我们使用 F2 种群的批量分离分析 (BSA) 来检测芽分枝的主要数量性状基因座 (QTL)，在芸苔 L 染色体 A09 的长臂上指定芽分枝 9 (qSB.A09) .ssp。中华。此外，传统的 F2 种群 QTL 作图揭示了不同区域的 6 个 QTL。其中，染色体 A09 上的作图区域与 BSA-seq 分析的结果一致，并且在 2 年的研究期间保持稳定，解释了多种遗传背景下 19.37% 和 22.18% 的表型变异。使用极端重组体，qSB.A09 被进一步划分为一个包含 28 个注释基因的 127 kb 基因组区域。我们随后将 GRAS 转录因子基因 Bra007056 鉴定为潜在的候选基因；Bra007056是控制水稻分蘖的关键基因MONOCULM 1 (MOC1)的直系同源物。定量 RT-PCR 进一步揭示 Bra007056 的表达与枝条分枝表型呈正相关。此外，Bra007056 特有的插入/缺失标记与 F2 群体中的枝条分枝性状共同分离。总体，这些结果为阐明油菜芽分枝的分子机制提供了依据。中华牧野。