Department of Plant Pathology, Cornell University, Ithaca, New York 14853-5908.
Appl Environ Microbiol. 1992 Mar;58(3):809-14. doi: 10.1128/aem.58.3.809-814.1992.
Chickpea (Cicer arietium L.) produces the antimicrobial compounds (phytoalexins) medicarpin and maackiain in response to infection by microorganisms. Nectria haematococca mating population (MP) VI, a fungus pathogenic on chickpea, can metabolize maackiain and medicarpin to less toxic products. These reactions are thought to be detoxification mechanisms in N. haematococca MP VI and required for pathogenesis by this fungus on chickpea. In the present study, these hypotheses were tested by examining the phenotypes of progeny from crosses of the fungus that segregated for genes (Mak genes) controlling phytoalexin metabolism. Mak1 and Mak2, two genes that individually confer the ability to convert maackiain to its 1a-hydroxydienone derivative, were linked to higher tolerance of the phytoalexins and high virulence on chickpea. These results indicate that this metabolic reaction is a mechanism for increased phytoalexin tolerance in the fungus, which thereby allows a higher virulence on chickpea. Mak3, a gene conferring the ability to convert maackiain to its 6a-hydroxypterocarpan derivative, also increased tolerance to maackiain in strains which carried it; however, the contribution of Mak3 to the overall level of pathogenesis could not be evaluated because most progeny from the cross segregating for this gene were low in virulence. Thus, metabolic detoxification of phytoalexins appeared to be necessary, as demonstrated in the Mak1 and Mak2 crosses, but not sufficient by itself, as in the Mak3 cross, for high virulence of N. haematococca MP VI on chickpea.
鹰嘴豆（Cicer arietinum L.）在受到微生物感染时会产生抗菌化合物（植物抗毒素） medicarpin 和 maackiain。豌豆炭疽病菌交配群体（MP）VI 是一种对鹰嘴豆致病的真菌，可以将 maackiain 和 medicarpin 代谢为毒性较低的产物。这些反应被认为是 N. haematococca MP VI 中的解毒机制，也是该真菌在鹰嘴豆上致病所必需的。在本研究中，通过检查分离出控制植物抗毒素代谢基因（Mak 基因）的真菌后代的表型来检验这些假设。Mak1 和 Mak2 是两个单独赋予将 maackiain 转化为 1a-羟二烯酮衍生物能力的基因，它们与对植物抗毒素的更高耐受性和对鹰嘴豆的高毒力相关。这些结果表明，这种代谢反应是真菌增加植物抗毒素耐受性的一种机制，从而使其对鹰嘴豆具有更高的毒力。Mak3 是一个赋予将 maackiain 转化为其 6a-羟紫檀烷衍生物能力的基因，它也增加了携带该基因的菌株对 maackiain 的耐受性；然而，由于该基因分离的大多数后代在毒力方面较低，因此无法评估 Mak3 对总体致病性水平的贡献。因此，正如在 Mak1 和 Mak2 杂交中所证明的那样，代谢解毒植物抗毒素似乎是必要的，但在 Mak3 杂交中，它本身并不足以使豌豆炭疽病菌 MP VI 对鹰嘴豆具有高毒力。
