Ecologie, Systématique et Evolution, Université Paris-Sud, F-91405 Orsay cedex, France.
Mol Ecol. 2010 Jan;19(2):292-306. doi: 10.1111/j.1365-294X.2009.04454.x. Epub 2009 Dec 8.
Numerous genes in diverse organisms have been shown to be under positive selection, especially genes involved in reproduction, adaptation to contrasting environments, hybrid inviability, and host-pathogen interactions. Looking for genes under positive selection in pathogens has been a priority in efforts to investigate coevolution dynamics and to develop vaccines or drugs. To elucidate the functions involved in host specialization, here we aimed at identifying candidate sequences that could have evolved under positive selection among closely related pathogens specialized on different hosts. For this goal, we sequenced c. 17,000-32,000 ESTs from each of four Microbotryum species, which are fungal pathogens responsible for anther smut disease on host plants in the Caryophyllaceae. Forty-two of the 372 predicted orthologous genes showed significant signal of positive selection, which represents a good number of candidate genes for further investigation. Sequencing 16 of these genes in 9 additional Microbotryum species confirmed that they have indeed been rapidly evolving in the pathogen species specialized on different hosts. The genes showing significant signals of positive selection were putatively involved in nutrient uptake from the host, secondary metabolite synthesis and secretion, respiration under stressful conditions and stress response, hyphal growth and differentiation, and regulation of expression by other genes. Many of these genes had transmembrane domains and may therefore also be involved in pathogen recognition by the host. Our approach thus revealed fruitful and should be feasible for many non-model organisms for which candidate genes for diversifying selection are needed.
许多不同生物的基因已经被证明受到正选择的影响，特别是那些与繁殖、适应不同环境、杂种不育和宿主-病原体相互作用相关的基因。在病原体中寻找受到正选择的基因一直是研究共同进化动态和开发疫苗或药物的重点。为了阐明与宿主特化相关的功能，我们旨在确定候选序列，这些序列可能在专门针对不同宿主的密切相关病原体中受到正选择的影响。为此，我们对四个 Microbotryum 物种的每个物种测序了约 17000-32000 个 EST，这些物种是引起石竹科植物花药黑粉病的真菌病原体。在 372 个预测的直系同源基因中，有 42 个显示出正选择的显著信号，这代表了许多候选基因，可供进一步研究。在 9 个其他 Microbotryum 物种中对其中 16 个基因进行测序，证实它们在专门针对不同宿主的病原体物种中确实在快速进化。显示出正选择显著信号的基因可能涉及从宿主中吸收营养、次生代谢物合成和分泌、应激条件下的呼吸和应激反应、菌丝生长和分化，以及其他基因的表达调控。这些基因中有许多具有跨膜结构域，因此也可能参与宿主对病原体的识别。我们的方法因此揭示了富有成效的结果，对于许多需要多样化选择候选基因的非模式生物来说，这种方法应该是可行的。
