Centre for Biological Sciences, Life Sciences, University of Southampton, Southampton, United Kingdom ; Current address: USDA Forest Service, National Forest Genetics Lab, 2480 Carson Road, Placerville, California, United States of America.
PLoS One. 2013 Nov 19;8(11):e79925. doi: 10.1371/journal.pone.0079925. eCollection 2013.
Identifying genetic sequences underlying insect associations on forest trees will improve the understanding of community genetics on a broad scale. We tested for genomic regions associated with insects in hybrid poplar using quantitative trait loci (QTL) analyses conducted on data from a common garden experiment. The F2 offspring of a hybrid poplar (Populus trichocarpa x P. deltoides) cross were assessed for seven categories of insect leaf damage at two time points, June and August. Positive and negative correlations were detected among damage categories and between sampling times. For example, sap suckers on leaves in June were positively correlated with sap suckers on leaves (P<0.001) but negatively correlated with skeletonizer damage (P<0.01) in August. The seven forms of leaf damage were used as a proxy for seven functional groups of insect species. Significant variation in insect association occurred among the hybrid offspring, including transgressive segregation of susceptibility to damage. NMDS analyses revealed significant variation and modest broad-sense heritability in insect community structure among genets. QTL analyses identified 14 genomic regions across 9 linkage groups that correlated with insect association. We used three genomics tools to test for putative mechanisms underlying the QTL. First, shikimate-phenylpropanoid pathway genes co-located to 9 of the 13 QTL tested, consistent with the role of phenolic glycosides as defensive compounds. Second, two insect association QTL corresponded to genomic hotspots for leaf trait QTL as identified in previous studies, indicating that, in addition to biochemical attributes, leaf morphology may influence insect preference. Third, network analyses identified categories of gene models over-represented in QTL for certain damage types, providing direction for future functional studies. These results provide insight into the genetic components involved in insect community structure in a fast-growing forest tree.
确定森林树木上昆虫共生的遗传序列将提高对广泛范围内群落遗传学的理解。我们使用来自共同田间试验的数据进行数量性状位点（QTL）分析，测试了杂交杨树上与昆虫相关的基因组区域。杂交杨（Populus trichocarpa x P. deltoides）杂交的 F2 后代在两个时间点（6 月和 8 月）评估了 7 种昆虫叶片损伤类别。在 6 月和 8 月，损伤类别之间以及采样时间之间检测到正相关和负相关。例如，6 月叶片上的汁液吸吮者与叶片上的汁液吸吮者呈正相关（P<0.001），但与 8 月的潜叶虫损伤呈负相关（P<0.01）。这 7 种叶片损伤形式被用作 7 种昆虫功能组的代表。杂交后代中昆虫共生的发生存在显著差异，包括对损伤易感性的超越分离。NMDS 分析显示，在遗传体之间，昆虫群落结构存在显著的变异和适度的广义遗传力。QTL 分析确定了 14 个与昆虫关联相关的基因组区域，分布在 9 个连锁群上。我们使用三种基因组学工具来测试 QTL 背后的潜在机制。首先，莽草酸-苯丙烷途径基因与 13 个测试的 QTL 中的 9 个共定位，这与酚糖苷作为防御化合物的作用一致。其次，两个昆虫关联 QTL 与之前研究中确定的叶片性状 QTL 的基因组热点相对应，表明除了生化特性外，叶片形态可能影响昆虫偏好。第三，网络分析确定了在某些损伤类型的 QTL 中过表达的基因模型类别，为未来的功能研究提供了方向。这些结果提供了对快速生长的森林树木中昆虫群落结构所涉及的遗传成分的深入了解。
