Evolution and differentiation of plant pathogenic fungi mediated by horizontal gene transfer.

植物-寄生物相互作用的特异性机制是现代植物病理学中最有趣的问题之一。虽然在大多数植物病害中决定这种特异性的关键因素是未知的，但已知某些真菌病原体产生宿主特异性毒素（HST）作为相容性决定因子。我们的研究旨在评估产生HST的互隔孢霉病原体的致病策略的进化。我们已经克隆并鉴定了一个基因（AMT），该基因在苹果致病型互隔孢霉的AM毒素生物合成中起着关键作用，并表明它是对易感苹果致病所必需的。我们还显示了一个聚酮合酶基因，ALT 1，其产物催化AAL毒素在番茄致病型A. alternata的生产。这些HST的生物合成基因驻留在条件反射（CD）染色体上发现，只有在致病性和HST生产菌株的互隔孢霉和同源基因没有检测到非致病性菌株的互隔孢霉。这表明，这些基因可能是通过水平基因转移获得的，并提供了一种可能的机制，使新的致病型可能在自然界中出现。

The mechanism for determining specificity in plant-parasite interactions is one of the most intriguing issues in modern plant pathology. Although key factors that determine such specificity are unknown in most plant diseases, certain fungal pathogens are known to produce host-specific toxins(HSTs) as compatibility determinants. Our research is aimed at assessing evolution of pathogenic strategy in A.alternata pathogens that produce HSTs. We have cloned and characterized a gene (AMT) that plays a crucial role in AM-toxin biosynthesis by the apple pathotype of A.alternata and shown that it is required for pathogenicity to susceptible apple. We have also shown a polyketide synthase gene, ALT1, whose product catalyzes the production of AAL-toxin in the tomato pathotype of A.alternata. These HST biosynthetic genes reside on conditionally dispensable(CD) chromosomes found only in the pathogenic and HST-producing strains of A.alternata and homologues of the genes were not detected in nonpathogenic strains of A.alternata. This suggests that these genes may have been acquired by horizontal gene transfer and provides a possible mechanism whereby new pathotypes could arise in nature.