QTL for Yield Traits and Their Association with Functional Genes in Response to Phosphorus Deficiency in Brassica napus

BackgroundOilseed rape (Brassica napus L.) is one of the most important oil crops. A primary limitation to the cultivation of this crop is the lack of available phosphorus (P) in soils. To elucidate the genetic control of P deficiency tolerance in Brassica napus, quantitative trait locus (QTL) for seed yield and yield related-traits in response to P deficiency were identified using a double haploid mapping population (TN DH) derived from a cross between a P-efficient cultivar, Ningyou 7 and a P-inefficient cultivar, Tapidor. ResultsThree field trials were conducted to determine seed yield (SY), plant height (PH), number of primary branches (BN), height to the first primary branch (FBH), relative first primary branch height (RBH), pod number per plant (PN), seed number per pod (SN) and seed weight of 1,000 seeds (SW) in 188 lines of TN DH population exposed to low P (LP) and optimal P (OP) conditions. P deficiency decreased PH, BN, SN, PN and SY, and increased FBH and RBH with no effect on SW. Three reproducible LP-specific QTL regions were identified on chromosomes A2, A3 and A5 that controlled SN, PN and SW respectively. In addition, six reproducible constitutive regions were also mapped with two each for SY-LP on A2, and FBH-LP on C6 and one each for PH-LP and SW-LP on A3. About 30 markers derived from 19 orthologous genes involved in Arabidopsis P homeostasis were mapped on 24 QTL regions by comparative mapping between Arabidopsis and Brassica napus. Among these genes, GPT1, MGD2 and SIZ1 were associated with two major loci regulating SY-LP and other yield-related traits on A2 between 77.1 and 95.0 cM. ConclusionThe stable QTLs detected under LP conditions and their candidate genes may provide useful information for marker-assisted selection in breeding high-yield B. napus varieties with improved P efficiency.

背景 油菜（Brassica napus L.）是全球最重要的油料作物之一。该作物规模化栽培面临的主要限制因素之一为土壤有效磷（P）供给匮乏。为阐明甘蓝型油菜耐低磷胁迫的遗传调控机制，本研究以磷高效品种宁油7号与磷低效品种Tapidor杂交构建的双单倍体（double haploid, DH）作图群体TN DH为材料，对响应低磷胁迫的种子产量及产量相关性状的数量性状位点（quantitative trait locus, QTL）进行了定位。
结果 本研究开展3组独立田间试验，在低磷（low P, LP）与适磷（optimal P, OP）培养条件下，对TN DH作图群体的188个株系的种子产量（seed yield, SY）、株高（plant height, PH）、一次分枝数（number of primary branches, BN）、第一分枝高度（height to the first primary branch, FBH）、相对第一分枝高度（relative first primary branch height, RBH）、单株荚果数（pod number per plant, PN）、每荚粒数（seed number per pod, SN）及千粒重（1000-seed weight, SW）进行了表型鉴定。结果表明，低磷胁迫显著降低了株高、一次分枝数、每荚粒数、单株荚果数与种子产量，同时提升了第一分枝高度与相对第一分枝高度，但对千粒重无显著影响。研究在A2、A3和A5染色体上分别鉴定到3个可重复的低磷特异性QTL区域，分别调控每荚粒数、单株荚果数及千粒重。此外，还定位到6个可重复的组成型QTL区域：其中A2染色体上的低磷处理种子产量（SY-LP）、C6染色体上的低磷处理第一分枝高度（FBH-LP）各包含2个位点，A3染色体上的低磷处理株高（PH-LP）与低磷处理千粒重（SW-LP）各包含1个位点。通过拟南芥与甘蓝型油菜的比较基因组定位分析，将源自19个参与拟南芥磷稳态调控的同源基因的约30个分子标记锚定至24个QTL区域。其中，GPT1、MGD2与SIZ1基因与A2染色体77.1~95.0 cM区间内调控低磷处理种子产量及其他产量相关性状的2个主效位点显著相关。
结论 本研究在低磷条件下鉴定到的稳定QTL及其候选基因，可为通过分子标记辅助选择培育高磷效率、高产的甘蓝型油菜品种提供极具价值的理论依据与技术支撑。