Genome-wide approach to dissecting the genetic basis of heterosis

杂种优势是指两个自交系之间的杂交后代相对于单亲或双亲具有更强的适合度或表现。它已经在植物育种和进化生物学中得到了成功的利用。然而，尽管在过去的几十年里，人们提出了多种模型来解释杂种优势，但其遗传基础在很大程度上仍然不清楚。这些模型未能解释杂种优势是由于缺乏关于全基因组杂合性和杂交基因组中杂种基因座上遗传效应分布的知识。在这里，我提出了一种新的方法来评估全基因组的杂合性和有助于杂种优势的遗传效应的分布。我会用油菜(Brassica napus L.)进行这样的评估。甘蓝型油菜(2n=38，AACC基因组)是由二倍体祖先种油菜(2n=20，AA基因组)与甘蓝(2n=18，CC基因组)杂交而来的，但由于驯化和集约化育种，其遗传多样性降低。我将配制三种类型的杂交组合：春油菜×春油菜(窄杂交)、春油菜×冬油菜(中间杂交)和春油菜×重组油菜品系(远交)。人工合成的品系是由油菜×甘蓝种间杂交获得的。三个杂交组合的亲本和杂交后代将使用SNP(单核苷酸多态性)阵列进行基因分型，并对总生物量和其他性状进行表型分析。将估计全基因组的杂合度。我将对不同基因作用模式下的SNP效应进行全基因组预测。预期的结果是：窄交的杂种优势与杂合度之间没有关系；(Ii)中间杂交的杂种优势与杂合度呈线性关系；(Iii)远缘杂交的杂种优势与杂合度呈非线性关系。建议的研究将极大地提高我们目前对油菜和其他植物杂种优势和近交衰退的遗传基础的理解。这也将对亲本系的基因组选择具有实用价值，以最大限度地提高杂交油菜的杂种优势量。油菜是一种主要作物，由于其产量和其他性状优于传统的自由授粉品种，正在加拿大和其他地方迅速扩大。

Heterosis is the phenomenon whereby the progeny of a cross between two inbred lines have enhanced fitness or performance relative to one or both parents. It has been successfully exploited in plant breeding and evolutionary biology. However, its genetic basis remains largely unknown despite the proposal of multiple models to explain heterosis over the past decades. The failure of these models to explain heterosis is due to lack of knowledge on genome-wide heterozygosity and the distribution of genetic effects at heterotic loci across the hybrid genome. Here I propose a novel approach to assessing genome-wide heterozygosity and the distribution of genetic effects contributing to heterosis. I will use canola (Brassica napus L.) for such assessment. B. napus (2n=38, AACC genome) originated from hybridization between diploid progenitor species B. rapa (2n=20, AA genome) and B. oleracea (2n=18, CC genome), but its genetic diversity is reduced due to domestication and intensive breeding. I will make three types of crosses: spring canola × spring canola (narrow cross), spring canola × winter canola (intermediate cross) and spring canola × resynthesized B. napus lines (wide cross). The resynthesized lines are derived from interspecific cross, B. rapa × B. oleracea. The parents and hybrid progeny from the three crosses will be genotyped using a SNP (single nucleotide polymorphism) array and phenotyped for the total biomass and other traits. Genome-wide heterozygosity will be estimated. I will conduct genome-wide prediction of SNP effects under different gene action models. The expected results are: no relationship between heterosis and heterozygosity in narrow cross; (ii) a linear relationship in intermediate cross; and (iii) nonlinear relationship in wide cross. The proposed research will significantly improve our current understanding of the genetic basis of heterosis and inbreeding depression in canola and other plant species. It will also be of practical value to genomic selection of parental lines for maximizing the amount of heterosis in hybrid canola, a major crop that is rapidly expanding in Canada and elsewhere due to its superiority of yield and other traits over traditional open-pollinated cultivars.