我国老百姓饭桌上常见的长豇豆可具有长达1米的长荚。然而在非洲,长豇豆的洋兄弟─普通豇豆的豆荚却只有人的手指般长短。是什么原因导致这种“两兄弟,大不同”的现象出现呢?
近日,英国《自然》出版集团旗下著名遗传学期刊《遗传》(Heredity)发表了我国科学家对长豇豆育种驯化的最新研究成果,认为亚洲人对豇豆三条特定染色体的持续人工选择是导致长豇豆超长豆荚形成的遗传主因。
浙江省农业科学院蔬菜所李国景研究员率领的团队在国家、浙江省自然科学基金和中美合作项目的资助下,利用1127个单核苷酸多态性(一种DNA变异)标记分析了我国95份长豇豆资源以及4份来自美国和非洲的普通豇豆DNA。通过以“全基因组连锁不平衡(LD)分析”为主的遗传学方法结合日本学者提出的“LD变异组分分解”,研究人员确定长豇豆和普通豇豆“本是同根生”,并推测出其兄弟当年“分道扬镳”的可能图景:最初豇豆的老祖宗生活在非洲,并且将种子供给当地人民作为蛋白质的主要来源。后来一小部分豇豆随人口流动迁移到了亚洲,但亚洲人并不喜欢吃它的豆子,却喜欢食用其嫩荚。于是人们一代代地选留那些荚长最长的豇豆种子进行繁殖,并且让它们彼此杂交并继续选择。千百年来,人们在不知不觉中对豇豆第5,7和11号染色体进行了高强度的定向选择,而控制豇豆荚长的基因正位于这些染色体上。最终,在亚洲形成了拥有可长达1米超级豆荚的豇豆新亚种—长豇豆亚种。该研究还首次提出在遗传上将长豇豆划分为“典型菜用型”和“非典型菜用型”两大类群,因为“它们存在着明显的遗传‘群体结构’”,论文第一作者徐沛副研究员解释说。
“可以说,双重‘建立者效应’(founder effect)+ 对特定染色体的高强度持续选择是长豇豆育种驯化过程中最显著的特点。这一过程反映的并不是 ‘进化’,而是强调了外部力量(人为选择)对生物多样性的影响”,徐沛博士最后总结说。(生物谷Bioon.com)
doi: 10.1038/hdy.2012.8
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Genome wide linkage disequilibrium in Chinese asparagus bean (Vigna. unguiculata ssp. sesquipedialis) germplasm: implications for domestication history and genome wide association studies
P Xu, X Wu, B Wang, J Luo, Y Liu, J D Ehlers, T J Close, P A Roberts, Z Lu, S Wang and G Li
Association mapping of important traits of crop plants relies on first understanding the extent and patterns of linkage disequilibrium (LD) in the particular germplasm being investigated. We characterize here the genetic diversity, population structure and genome wide LD patterns in a set of asparagus bean (Vigna. unguiculata ssp. sesquipedialis) germplasm from China. A diverse collection of 99 asparagus bean and normal cowpea accessions were genotyped with 1127 expressed sequence tag-derived single nucleotide polymorphism markers (SNPs). The proportion of polymorphic SNPs across the collection was relatively low (39%), with an average number of SNPs per locus of 1.33. Bayesian population structure analysis indicated two subdivisions within the collection sampled that generally represented the ‘standard vegetable’ type (subgroup SV) and the ‘non-standard vegetable’ type (subgroup NSV), respectively. Level of LD (r2) was higher and extent of LD persisted longer in subgroup SV than in subgroup NSV, whereas LD decayed rapidly (0–2?cM) in both subgroups. LD decay distance varied among chromosomes, with the longest (≈5?cM) five times longer than the shortest (≈1?cM). Partitioning of LD variance into within- and between-subgroup components coupled with comparative LD decay analysis suggested that linkage group 5, 7 and 10 may have undergone the most intensive epistatic selection toward traits favorable for vegetable use. This work provides a first population genetic insight into domestication history of asparagus bean and demonstrates the feasibility of mapping complex traits by genome wide association study in asparagus bean using a currently available cowpea SNPs marker platform