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

红松天然杂交种的正确鉴定前大声。和P.bansiana Lamb.(PCBC)对于评估它们的进化意义至关重要。尽管几十年来进行了大量的形态、生化和分子研究，但从这个杂交区鉴定杂交种仍然很困难，主要原因有两个。首先，经典的Anderson杂交指数或相似的形态计量学指数是基于杂交种与其亲本物种之间显著的表型差异，但所观察到的性状相关性和形态中介可能源于进化现象(例如，两个分离物种的祖先种群的残余)，而不是杂交本身。第二，亲本类型缺乏独特的分子标记和PCBC群体间的遗传亲缘关系密切，并没有显著提高形态性状区分杂种和亲本的能力。最近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(SNP)标记，这增加了全基因组关联研究的前景。然而，由于异交松基因组大(约300亿碱基)和连锁不平衡的快速衰减(在1000碱基以内或更快)，候选基因方法更适合于这些针叶树。在这项提议中，我将开发一个从负担得起的丰富SNPs到明确识别PCBC复合体中的杂交种和亲本个体和群体的‘准基因组范围’的抗旱性杂交指数。我将使用总树高作为替代指标来测量36个PCBC种群对干旱的反应的表型差异。然后，将用不同混合模式下所有SNP标记的遗传型值(育种)的总和来预测‘准全基因组’的抗旱性杂交指数。所提出的用于鉴定杂种的关联遗传学方法使用了最新的混合模型发展，允许将适应性状的信息与SNP标记相结合，因此是朝着解决天然杂交种分类和使用的长期问题迈出的重要一步。

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.