Bertier Lien, Leus Leen, D'hondt Liesbet, de Cock Arthur W A M, Höfte Monica
Department of Crop Protection, Ghent University, Ghent, Belgium.
Plant Sciences Unit, Applied Genetics and Breeding, Institute for Agricultural and Fisheries Research (ILVO), Melle, Belgium.
PLoS One. 2013 Dec 26;8(12):e85385. doi: 10.1371/journal.pone.0085385. eCollection 2013.
It is becoming increasingly evident that interspecific hybridization is a common event in phytophthora evolution. Yet, the fundamental processes underlying interspecific hybridization and the consequences for its ecological fitness and distribution are not well understood. We studied hybridization events in phytophthora clade 8b. This is a cold-tolerant group of plant pathogenic oomycetes in which six host-specific species have been described that mostly attack winter-grown vegetables. Hybrid characterization was done by sequencing and cloning of two nuclear (ITS and Ypt1) and two mitochondrial loci (Cox1 and Nadh1) combined with DNA content estimation using flow cytometry. Three different mtDNA haplotypes were recovered among the presumed hybrid isolates, dividing the hybrids into three types, with different parental species involved. In the nuclear genes, additivity, i.e. the presence of two alleles coming from different parents, was detected. Hybrid isolates showed large variations in DNA content, which was positively correlated with the additivity in nuclear loci, indicating allopolyploid hybridization followed by a process of diploidization. Moreover, indications of homeologous recombination were found in the hybrids by cloning ITS products. The hybrid isolates have been isolated from a range of hosts that have not been reported previously for clade 8b species, indicating that they have novel pathogenic potential. Next to this, DNA content measurements of the non-hybrid clade 8b species suggest that polyploidy is a common feature of this clade. We hypothesize that interspecific hybridization and polyploidy are two linked phenomena in phytophthora, and that these processes might play an important and ongoing role in the evolution of this genus.
越来越明显的是，种间杂交在疫霉属进化中是一个常见事件。然而，种间杂交背后的基本过程及其对生态适应性和分布的影响尚未得到很好的理解。我们研究了疫霉属进化枝8b中的杂交事件。这是一组耐寒的植物病原卵菌，其中已描述了六个寄主特异性物种，它们大多攻击冬季生长的蔬菜。通过对两个核基因座（ITS和Ypt1）和两个线粒体基因座（Cox1和Nadh1）进行测序和克隆，并结合使用流式细胞术估计DNA含量来进行杂种鉴定。在假定的杂种分离物中发现了三种不同的线粒体DNA单倍型，将杂种分为三种类型，涉及不同的亲本物种。在核基因中，检测到了加性，即存在来自不同亲本的两个等位基因。杂种分离物的DNA含量显示出很大差异，这与核基因座中的加性呈正相关，表明是异源多倍体杂交，随后是二倍体化过程。此外，通过克隆ITS产物在杂种中发现了同源重组的迹象。杂种分离物已从一系列以前未报道过进化枝8b物种的寄主中分离出来，这表明它们具有新的致病潜力。除此之外，对非杂种进化枝8b物种的DNA含量测量表明，多倍体是该进化枝的一个共同特征。我们假设种间杂交和多倍体是疫霉属中的两个相关现象，并且这些过程可能在该属的进化中发挥重要且持续的作用。
