PBJ: 油菜遗传育种首席科学家王汉中院士揭示杂种优势“聚合”新机制

杂种优势利用的核心在于“聚”而不是“杂”。这是日前中国农科院油料所油菜遗传育种创新团队首席科学家王汉中院士带领科研人员揭示的“聚合”新机制，为促进杂种优势的进一步利用提供了新的理论指导。相关研究成果发表在国际期刊《植物生物技术》（Plant Biotechnology Journal）上。

油菜杂种优势利用的核心在于优异等位基因的聚合。油料所供图

论文共同通讯作者、油料所副研究员师家勤介绍，杂种优势是杂交子代在生活力、适应性、抗性和产量等方面优于亲本的一种普遍生物学现象，利用这一现象培育杂交品种成为提高农业动植物生产力的重要途径。杂种优势利用的潜在理论基础是来自双亲的等位基因杂合后会有更优势的表现，但研究发现杂交品种的基因杂合程度与其杂种优势水平的相关性普遍偏低。

油菜是我国产油量最大的油料作物，低芥酸菜籽油是脂肪酸组成较合理的大宗食用油，在国家食用油供给安全中具有十分重要的战略地位。目前全世界油菜杂交种的占比超过70%，然而其遗传机制的研究相对滞后。该研究利用一个代表性的油菜组合从表型、遗传和分子层面进行了多年系统研究。

研究发现，一个基因杂合后的表现大多不超过高值亲本，但优异等位基因分别来自不同亲本的多个基因杂合后的表现因互补和累加效应可以超过高值亲本，并且多个产量构成性状的杂种优势连乘效应可以产生产量的强优势。

上述结果表明，为获得最优的杂交组合，最重要的原则不是增加亲本间的遗传距离，而是尽可能多的聚合优势基因，无论其是杂合还是纯合状态。这一结论突破了认识误区，为选育强优势杂交种指明了方向。

该团队已毕业博士生叶姜和梁华兵为论文共同第一作者，王汉中和师家勤为共同通讯作者。该研究得到国家重点研发计划和中国农科院科技创新工程重大任务等项目的资助。

Heterosis refers to the better performance of cross progeny compared with inbred parents, and its utilization contributes greatly to agricultural production. Several hypotheses have been proposed to explain heterosis mainly including dominance, over-dominance (or pseudooverdominance) and epistasis. However, systematic dissection and verification of these hypotheses are rarely documented. Here, comparison of heterosis level across different traits showed that the strong heterosis of composite traits (such as yield) could be attributed to the multiplicative effects of moderate heterosis of component traits, whether at the genome or locus level. Yield heterosis was regulated by a complex trait-QTL network that was characterized by obvious centre-periphery structure, hub QTL, complex up/downstream and positive/negative feedback relationships. More importantly, we showed that better-parent heterosis on yield could be produced in a cross of two near-isogenic lines by the pyramiding and complementation of two major heterotic QTL showing partial-dominance on yield components. The causal gene (BnaA9.CYP78A9) of QC14 was identified, and its heterotic effect results from the heterozygous status of a CACTA-like transposable element in its upstream regulatory region, which led to partial dominance at expression and auxin levels, thus resulting in non-additive expression of downstream responsive genes involved in cell cycle and proliferation, eventually leading to the heterosis of cell number. Taken together, the results at the phenotypic, genetic and molecular levels were highly consistent, which demonstrated that the pyramiding effect of heterotic QTL and the multiplicative effect of individual component traits could well explain substantial parts of yield heterosis in oilseed rape. These results provide in-depth insights into the genetic architecture and molecular mechanism of yield heterosis.

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