Association genetics approach to identification of hybrids in pinus contorta - pinus banksiana complex

扭曲松自然杂种的正确鉴定。练习大声。和P. banksiana Lamb。（PCBC）对于评估它们的进化意义至关重要。尽管在过去的几十年里进行了大量的形态学、生物化学和分子研究，但从这个杂交带鉴定杂种仍然很困难，主要有两个原因。首先，经典的安德森杂交指数或类似的形态计量指数是基于杂交物种与其亲本物种之间显著的表型差异，但观察到的性状相关性和形态中间性可能来自进化现象（例如，两个分离物种的祖先种群的残余），而不是杂交本身。其次，由于缺乏独特的亲本基因型分子标记，以及PCBC居群间的亲缘关系较近，使得形态性状区分杂种与亲本的能力没有显著提高。近年来，在包括松树在内的许多物种中发现了大量的单核苷酸多态性（SNP）标记，这为全基因组关联研究提供了前景。然而，由于异交松的基因组大（约300亿bp）和连锁不平衡的快速衰减（在1000 bp或更快），候选基因方法更适合于这些针叶树。在本提案中，我将开发一个“准全基因组”的耐旱性杂交指数，从负担得起的和丰富的snp到明确鉴定PCBC复合物中的杂交种和亲本个体和群体。我将使用总树高作为代理来测量36个PCBC种群在干旱响应中的表型变异。然后，“准全基因组”耐旱性杂交指数将被预测为不同混合模型下所有SNP标记的基因型（育种）值的总和。提出的关联遗传学方法用于鉴定杂交种，使用了最新的混合模型发展，允许将适应性性状信息与SNP标记相结合，因此是解决长期存在的分类和使用天然杂交种问题的重要一步。

Correct identification of natural hybrids between Pinus contorta Dougl. ex Loud. and P. banksiana Lamb. (PCBC) is essential for assessing their evolutionary significance. Despite numerous morphological, biochemical and molecular studies conducted over decades, hybrids identification from this hybrid zone remains difficult for two main reasons. First, classic Anderson's hybrid index or similar morphometric indices are based on marked phenotypic differences between hybrids and their parental species but the observed character correlation and morphological intermediacy could arise from evolutionary phenomena (e.g., remnants of ancestral population of two isolated species) other than hybridization per se. Second, a lack of unique molecular markers for parental genotypes and the close genetic affinity among PCBC populations have not significantly improved the capability of morphological characters to separate hybrids from the parental species. Recent advances in discovery of vast numbers of single nucleotide polymorphism (SNP) markers in many species including pines have raised prospects of genomewide association studies. However, due to the large genome sizes (~30 billion bp) and rapid decay of linkage disequilibrium (within 1000 bp or faster) in outcrossing pines, a candidate gene approach is more appropriate for these conifers. In this proposal, I will develop a 'quais-genomewide' hybrid index for drought tolerance from affordable and abundant SNPs towards unambiguous identification of hybrids and parental individuals and populations in PCBC complex. I will use total tree height as a surrogate to measure phenotypic variation among 36 PCBC populations in response to drought. The 'quasi-genomewide' hybrid index for drought tolerance will be then predicted as the sum of genotypic (breeding) values across all SNP markers under different mixed models. The proposed association genetics approach to identification of hybrids uses the latest mixed-model developments that allow for combining the information of adaptive traits with SNP markers and thus is a major step towards resolving a longstanding issue of classification and use of natural hybrids.