Genome-wide approach to dissecting the genetic basis of heterosis

杂种优势是两个自交系杂交的后代相对于一个或两个亲本具有更高的适应性或性能的现象。它已成功地应用于植物育种和进化生物学。然而，尽管在过去的几十年里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未知。这些模型无法解释杂种优势是由于缺乏对全基因组杂合性和杂种基因组中杂种优势位点遗传效应分布的了解。在这里，我提出了一种新的方法来评估全基因组杂合性和遗传效应的分布，有助于杂种优势。我将使用油菜（Brassica napus L.）进行评估。B. napus （2n=38， AACC基因组）起源于二倍体祖种B. rapa （2n=20， AA基因组）和B. oleracea （2n=18， CC基因组）的杂交，但由于驯化和集约化育种，其遗传多样性降低。我将做三种杂交：春油菜×春油菜（窄杂交）、春油菜×冬油菜（中间杂交）和春油菜×再合成甘蓝型油菜系（宽杂交）。重组系由种间杂交获得。将利用单核苷酸多态性（SNP）阵列对亲本和杂交后代进行基因分型，并对总生物量和其他性状进行表型分析。估计全基因组杂合性。对不同基因作用模式下的SNP效应进行全基因组预测。预期结果为：窄交杂种优势与杂合度不相关；（ii）中间交叉呈线性关系；(3)宽交叉非线性关系。本研究将显著提高我们对油菜等植物杂种优势和近交抑制的遗传基础的认识。杂交油菜是一种主要作物，由于其产量和其他性状优于传统的开放授粉品种，因此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.