Sillo Fabiano, Garbelotto Matteo, Friedman Maria, Gonthier Paolo
Department of Agricultural, Forest and Food Sciences, University of Torino, Grugliasco, Italy.
Department of Environmental Science, Policy and Management, University of California, Berkeley.
Genome Biol Evol. 2015 Nov 1;7(12):3190-206. doi: 10.1093/gbe/evv209.
It has been estimated that the sister plant pathogenic fungal species Heterobasidion irregulare and Heterobasidion annosum may have been allopatrically isolated for 34-41 Myr. They are now sympatric due to the introduction of the first species from North America into Italy, where they freely hybridize. We used a comparative genomic approach to 1) confirm that the two species are distinct at the genomic level; 2) determine which gene groups have diverged the most and the least between species; 3) show that their overall genomic structures are similar, as predicted by the viability of hybrids, and identify genomic regions that instead are incongruent; and 4) test the previously formulated hypothesis that genes involved in pathogenicity may be less divergent between the two species than genes involved in saprobic decay and sporulation. Results based on the sequencing of three genomes per species identified a high level of interspecific similarity, but clearly confirmed the status of the two as distinct taxa. Genes involved in pathogenicity were more conserved between species than genes involved in saprobic growth and sporulation, corroborating at the genomic level that invasiveness may be determined by the two latter traits, as documented by field and inoculation studies. Additionally, the majority of genes under positive selection and the majority of genes bearing interspecific structural variations were involved either in transcriptional or in mitochondrial functions. This study provides genomic-level evidence that invasiveness of pathogenic microbes can be attained without the high levels of pathogenicity presumed to exist for pathogens challenging naïve hosts.
据估计，姊妹植物病原真菌物种不规则异担子菌和多年异担子菌可能已经异域隔离了3400 - 4100万年。由于第一种物种从北美引入意大利，它们现在同域分布，并在那里自由杂交。我们采用了比较基因组学方法来：1）确认这两个物种在基因组水平上是不同的；2）确定物种间哪些基因组的差异最大和最小；3）表明它们的整体基因组结构相似，正如杂种的生存能力所预测的那样，并识别出不一致的基因组区域；4）检验先前提出的假设，即与致病性相关的基因在这两个物种之间的差异可能小于与腐生衰变和孢子形成相关的基因。基于每个物种三个基因组测序的结果显示出种间相似性较高，但明确证实了这两个物种作为不同分类单元的地位。与致病性相关的基因在物种间比与腐生生长和孢子形成相关的基因更保守，这在基因组水平上证实了入侵性可能由后两个特征决定，正如田间和接种研究所记录的那样。此外，大多数受到正选择的基因和大多数具有种间结构变异的基因都涉及转录或线粒体功能。这项研究提供了基因组水平的证据，表明致病微生物的入侵性可以在不存在针对未接触过病原体的宿主所假定的高致病性的情况下实现。
