Weber Isabella, Gruber Christian, Steinberg Gero
Max-Planck-Institut für Terrestrische Mikrobiologie, D-35043 Marburg, Germany.
Plant Cell. 2003 Dec;15(12):2826-42. doi: 10.1105/tpc.016246. Epub 2003 Nov 13.
In the early stages of plant infection, yeast-like haploid sporidia of Ustilago maydis respond to pheromone secreted by compatible partners by forming conjugation tubes. These then fuse to generate a dikaryotic hypha that forms appressoria to penetrate the host plant. As a first step toward understanding the structural requirements for these transitions, we have identified myo5, which encodes a class-V myosin. Analysis of conditional and null mutants revealed that Myo5 plays nonessential roles in cytokinesis and morphogenesis in sporidia and is required for hyphal morphology. Consistent with a role in morphogenesis, a functional green fluorescent protein-Myo5 fusion protein localized to the bud tip and the hyphal apex as well as to the septa and the spore wall during later stages of infection. However, the loss of Myo5 did not affect the tip growth of hyphae and sporidia. By contrast, Myo5 was indispensable for conjugation tube formation. Furthermore, myo5 mutants were impaired in the perception of pheromones, which indicates a particular importance of Myo5 in the mating process. Consequently, few mutant hyphae were formed that penetrated the plant epidermis but did not continue invasive growth. These results indicate a crucial role of Myo5 in the morphogenesis, dimorphic switch, and pathogenicity of U. maydis.
在植物感染的早期阶段，玉米黑粉菌的酵母样单倍体担孢子会通过形成接合管来响应由相容配偶体分泌的信息素。这些接合管随后融合形成双核菌丝，该双核菌丝会形成附着胞以穿透宿主植物。作为理解这些转变的结构要求的第一步，我们鉴定出了肌球蛋白5（myo5），它编码一种V类肌球蛋白。对条件性突变体和缺失突变体的分析表明，Myo5在担孢子的胞质分裂和形态发生中发挥非必需作用，但对菌丝形态是必需的。与在形态发生中的作用一致，一种功能性绿色荧光蛋白 - Myo5融合蛋白在感染后期定位于芽尖、菌丝顶端以及隔膜和孢子壁。然而，Myo5的缺失并不影响菌丝和担孢子的顶端生长。相比之下，Myo5对于接合管的形成是不可或缺的。此外，myo5突变体在信息素感知方面存在缺陷，这表明Myo5在交配过程中具有特殊重要性。因此，形成的能够穿透植物表皮但不继续进行侵入性生长的突变菌丝很少。这些结果表明Myo5在玉米黑粉菌的形态发生、二态转换和致病性中起着关键作用。
