Abstract：
Apple scab, caused by the hemibiotrophic fungus Venturia inaequalis, is currently the most common and damaging disease in apple orchards. Two strains of V. inaequalis (S755 and Rs552) with different sensitivities to azole fungicides and the bacterial metabolite fengycin were compared to determine the mechanisms responsible for these differences. Antifungal activity tests showed that Rs552 had reduced sensitivity to tebuconazole and tetraconazole, as well as to fengycin alone or in a binary mixture with other lipopeptides (iturin A, pumilacidin, lichenysin). S755 was highly sensitive to fengycin, whose activity was close to that of tebuconazole. Unlike fengycin, lipopeptides from the iturin family (mycosubtilin, iturin A) had similar activity on both strains, while those from the surfactin family (lichenysin, pumilacidin) were not active, except in binary mixtures with fengycin. The activity of lipopeptides varies according to their family and structure. Analyses to determine the difference in sensitivity to azoles (which target the CYP51 enzyme involved in the ergosterol biosynthesis pathway) showed that the reduced sensitivity in Rs552 is linked to (i) a constitutive increased expression of the Cyp51A gene caused by insertions in the upstream region and (ii) greater efflux by membrane pumps with the involvement of ABC transporters. Microscopic observations revealed that fengycin, known to interact with plasma membranes, induced morphological and cytological changes in cells from both strains. Sterol and phospholipid analyses showed a higher level of ergosta-7,22-dien-3-ol and a lower level of PI(C16:0/C18:1) in Rs552 compared with S755. These differences could therefore influence the composition of the plasma membrane and explain the differential sensitivity of the strains to fengycin. However, the similar antifungal activities of mycosubtilin and iturin A in the two strains indirectly indicate that sterols are probably not involved in the fengycin resistance mechanism. This leads to the conclusion that different mechanisms are responsible for the difference in susceptibility to azoles or fengycin in the strains studied.
摘要：
苹果结痂,由半营养真菌Venturiainaequalis引起的，是目前苹果园中最常见和最具破坏性的疾病。比较了对唑类杀真菌剂和细菌代谢物fengcin具有不同敏感性的两株V.inaequalis（S755和Rs552），以确定导致这些差异的机制。抗真菌活性测试表明，Rs552对戊唑醇和四曲康唑的敏感性降低，以及单独使用芬霉素或与其他脂肽的二元混合物（iturinA，pumilacidin,地衣素)。S755对芬霉素高度敏感，其活性接近戊唑醇。不像芬霉素,来自iturin家族的脂肽（mycosubtilin，iturinA）对两种菌株具有相似的活性，而那些来自surfactin家族的人(地衣素，短暂性)不活跃，除了与芬霉素的二元混合物。脂肽的活性根据其家族和结构而变化。确定对唑类（靶向麦角固醇生物合成途径中涉及的CYP51酶）敏感性差异的分析显示，Rs552的敏感性降低与（i）由上游区域的插入引起的Cyp51A基因的组成型表达增加和（ii）膜泵在ABC转运蛋白的参与下产生更大的外排。显微镜观察显示，芬霉素，已知与质膜相互作用，诱导两种菌株细胞的形态和细胞学变化。甾醇和磷脂分析显示，与S755相比，Rs552中的ergosta-7,22-dien-3-ol水平较高，PI水平较低（C16：0/C18：1）。因此，这些差异可能会影响质膜的组成，并解释了菌株对芬霉素的敏感性差异。然而,在这两个菌株中，枯草杆菌素和iturinA具有相似的抗真菌活性，间接表明固醇可能不参与风霉素的耐药机制。这得出的结论是，不同的机制是导致所研究菌株对唑类或芬霉素敏感性差异的原因。
