Biology Department, University of California, Riverside, California, USA.
Appl Environ Microbiol. 2014 Feb;80(3):1159-69. doi: 10.1128/AEM.02920-13. Epub 2013 Dec 2.
The bacterial pathogen Xylella fastidiosa infects xylem and causes disease in many plant species in the Americas. Different subspecies of this bacterium and different genotypes within subspecies infect different plant hosts, but the genetics of host adaptation are unknown. Here we examined the hypothesis that the introduction of novel genetic variation via intersubspecific homologous recombination (IHR) facilitates host shifts. We investigated IHR in 33 X. fastidiosa subsp. multiplex isolates previously identified as recombinant based on 8 loci (7 multilocus sequence typing [MLST] loci plus 1 locus). We found significant evidence of introgression from X. fastidiosa subsp. fastidiosa in 4 of the loci and, using published data, evidence of IHR in 6 of 9 additional loci. Our data showed that IHR regions in 2 of the 4 loci were inconsistent (12 mismatches) with X. fastidiosa subsp. fastidiosa alleles found in the United States but consistent with alleles from Central America. The other two loci were consistent with alleles from both regions. We propose that the recombinant forms all originated via genomewide recombination of one X. fastidiosa subsp. multiplex ancestor with one X. fastidiosa subsp. fastidiosa donor from Central America that was introduced into the United States but subsequently disappeared. Using all of the available data, 5 plant hosts of the recombinant types were identified, 3 of which also supported non-IHR X. fastidiosa subsp. multiplex, but 2 were unique to recombinant types from blueberry (7 isolates from Georgia, 3 from Florida); and blackberry (1 each from Florida and North Carolina), strongly supporting the hypothesis that IHR facilitated a host shift to blueberry and possibly blackberry.
细菌病原体韧皮部坏死病菌（Xylella fastidiosa）感染木质部并导致美洲许多植物物种患病。该细菌的不同亚种和亚种内的不同基因型感染不同的植物宿主，但宿主适应性的遗传机制尚不清楚。在这里，我们检验了这样一种假设，即通过种间同源重组（IHR）引入新的遗传变异有助于宿主转移。我们研究了 33 个先前根据 8 个基因座（7 个多位点序列分型 [MLST] 基因座加上 1 个基因座）确定为重组的 X. fastidiosa subsp. multiplex 分离株中的 IHR。我们在 4 个基因座中发现了来自 X. fastidiosa subsp. fastidiosa 的基因渗入的显著证据，并且使用已发表的数据，在另外 6 个基因座中的 9 个基因座中发现了 IHR 的证据。我们的数据表明，在 4 个基因座中的 2 个基因座中，IHR 区域与在美国发现的 X. fastidiosa subsp. fastidiosa 等位基因不一致（12 个错配），但与中美洲的等位基因一致。另外两个基因座与两个地区的等位基因一致。我们提出，所有重组形式都起源于一个 X. fastidiosa subsp. multiplex 祖先与一个从中美洲引入美国但随后消失的 X. fastidiosa subsp. fastidiosa 供体的全基因组重组。利用所有可用数据，鉴定了重组类型的 5 种植物宿主，其中 3 种也支持非 IHR X. fastidiosa subsp. multiplex，但 2 种仅存在于蓝莓（格鲁吉亚的 7 个分离株，佛罗里达州的 3 个分离株）和黑莓（佛罗里达州和北卡罗来纳州各 1 个分离株）的重组类型中，这强烈支持了 IHR 促进了蓝莓和可能黑莓的宿主转移的假设。
