Werner Stefan, Sugui Janyce A, Steinberg Gero, Deising Holger B
Institute of Agricultural and Nutritional Sciences, Martin-Luther-Universität-Halle-Wittenberg, Halle (Saale), Germany.
Mol Plant Microbe Interact. 2007 Dec;20(12):1555-67. doi: 10.1094/MPMI-20-12-1555.
Chitin synthesis contributes to cell wall biogenesis and is essential for invasion of solid substrata and pathogenicity of filamentous fungi. In contrast to yeasts, filamentous fungi contain up to 10 chitin synthases (CHS), which might reflect overlapping functions and indicate their complex lifestyle. Previous studies have shown that a class VI CHS of the maize anthracnose fungus Colletotrichum graminicola is essential for cell wall synthesis of conidia and vegetative hyphae. Here, we report on cloning and characterization of three additional CHS genes, CgChsI, CgChsIII, and CgChsV, encoding class I, III, and V CHS, respectively. All CHS genes are expressed during vegetative and pathogenic development. DeltaCgChsI and DeltaCgChsIII mutants did not differ significantly from the wild-type isolate with respect to hyphal growth and pathogenicity. In contrast, null mutants in the CgChsV gene, which encodes a CHS with an N-terminal myosin-like motor domain, are strongly impaired in vegetative growth and pathogenicity. Even in osmotically stabilized media, vegetative hyphae of DeltaCgChsV mutants exhibited large balloon-like swellings, appressorial walls appeared to disintegrate during maturation, and infection cells were nonfunctional. Surprisingly, DeltaCgChsV mutants were able to form dome-shaped hyphopodia that exerted force and showed host cell wall penetration rates comparable with the wild type. However, infection hyphae that formed within the plant cells exhibited severe swellings and were not able to proceed with plant colonization efficiently. Consequently, DeltaCgChsV mutants did not develop macroscopically visible anthracnose disease symptoms and, thus, were nonpathogenic.
几丁质合成有助于细胞壁生物合成，对于丝状真菌侵入固体基质和致病性至关重要。与酵母不同，丝状真菌含有多达10种几丁质合成酶（CHS），这可能反映了其功能重叠，并表明它们具有复杂的生活方式。先前的研究表明，玉米炭疽病菌禾谷炭疽菌的VI类CHS对于分生孢子和营养菌丝的细胞壁合成至关重要。在这里，我们报告另外三个CHS基因CgChsI、CgChsIII和CgChsV的克隆和特性分析，它们分别编码I类、III类和V类CHS。所有CHS基因在营养生长和致病发育过程中均有表达。DeltaCgChsI和DeltaCgChsIII突变体在菌丝生长和致病性方面与野生型分离株没有显著差异。相比之下，编码具有N端肌球蛋白样运动结构域的CHS的CgChsV基因的缺失突变体在营养生长和致病性方面受到严重损害。即使在渗透稳定的培养基中，DeltaCgChsV突变体的营养菌丝也会出现大的气球状肿胀，附着胞壁在成熟过程中似乎会解体，并且感染细胞无功能。令人惊讶的是，DeltaCgChsV突变体能够形成施加力的圆顶形菌丝状附着器，并且显示出与野生型相当的宿主细胞壁穿透率。然而，在植物细胞内形成的侵染菌丝表现出严重肿胀，并且无法有效地进行植物定殖。因此，DeltaCgChsV突变体没有出现宏观可见的炭疽病症状，因此是非致病性的。
