Mapping and molecular marker development for the BnaSBT gene controlling inflorescence and plant architectures in B. napus

Exploring the molecular mechanism underlying plant architecture and breeding new varieties suitable for mechanized harvesting are primary objectives for rapeseed breeders in China. However, few genes controlling plant architecture have been cloned in Brassica napus. In this study, SX3, a scattered-bud B. napus line with a dwarf and compact plant architecture, was characterized. To identify the genes underlying bud arrangement, plant height and branch angle, segregating populations were constructed by crossing SX3 with two clustered-bud lines with a tall and loose plant architecture. Genetic analysis revealed that the scattered-bud trait (SBT) was controlled by a single dominant gene, BnaSBT. BnaSBT is likely a pleiotropic gene that simultaneously controls plant height and branch angle. Using BSA-seq analysis, BnaSBT was mapped to a 4.15 Mb region on ChrA10. Owing to the lack of recombinants within this region, it was infeasible to finely map BnaSBT. RNA-seq analysis of BC2 plants with contrasting inflorescence and plant architectures revealed that the upregulation of genes involved in amino acid and lipid metabolism and genes encoding MADS-box transcription factors is related to the the phenotype of SX3. These findings together with comparative sequencing indicated that BnaA10.SEP1, BnaA10.AGL15, BnaA10.GLN1-4 and BnaA10.AGP15 are candidate genes for BnaSBT. Markers closely linked to the scattered-bud trait were developed for selecting dwarf and compact plants. These findings provide molecular markers and germplasms for breeding new varieties with ideal plant types and lay a theoretical foundation for cloning key genes and elucidating the genetic basis of inflorescence and plant architectures in B. napus. Overall design: RNA-seq profiling of whole apical meristem from wildtype(ZS11), Natural mutant(SX3), and their BC2 individuals (Zlike and Slike) with contrasting inflorescence and plant architectures at the developmental transition from inflorescence primordium differentiation to floral primordium initiation

解析株型分子机制、培育适宜机械化收获的新品种是中国油菜育种工作者的核心目标。然而，目前在甘蓝型油菜（Brassica napus）中已克隆的控制株型的基因寥寥无几。本研究对一株兼具矮化紧凑株型的散花蕾甘蓝型油菜品系SX3进行了特征分析。为鉴定调控花蕾排布、株高及分枝角度的基因，研究人员将SX3与两株株型高大松散的聚花蕾品系杂交，构建了分离群体。遗传分析结果显示，散花蕾性状（scattered-bud trait, SBT）由单个显性基因BnaSBT控制，该基因极有可能为同时调控株高与分枝角度的多效基因。通过BSA-seq分析，BnaSBT被定位到ChrA10染色体上一段4.15 Mb的区域内。由于该区域内缺乏重组体，无法对BnaSBT进行精细定位。对具有相反花序与株型特征的BC2代植株进行RNA-seq分析后发现，参与氨基酸与脂质代谢的基因，以及编码MADS-box转录因子的基因的上调表达，与SX3的表型密切相关。结合比较测序结果，本研究确定BnaA10.SEP1、BnaA10.AGL15、BnaA10.GLN1-4及BnaA10.AGP15为BnaSBT的候选基因。研究人员开发了与散花蕾性状紧密连锁的分子标记，用于筛选矮化紧凑株型植株。本研究结果为培育理想株型的油菜新品种提供了分子标记与种质资源，同时为克隆甘蓝型油菜关键功能基因、解析花序与株型的遗传基础奠定了理论基础。实验整体设计：在花序原基分化至花原基起始的发育转换阶段，采集野生型（ZS11）、自然突变体（SX3）以及二者的BC2代个体（Zlike与Slike，二者具有相反的花序与株型特征）的全株顶端分生组织，进行RNA-seq转录组分析。