Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
Fungal Genet Biol. 2012 Nov;49(11):967-75. doi: 10.1016/j.fgb.2012.08.009. Epub 2012 Sep 12.
The conidia of Colletotrichum orbiculare, the causal agent of cucumber anthracnose, develop appressoria that are pigmented with melanin for host plant infection. Premature appressoria contain abundant lipid droplets (LDs), but these disappear during appressorial maturation, indicating lipolysis inside the appressorial cells. The lipolysis and melanization in appressoria require the peroxin PEX6, suggesting the importance of peroxisomal metabolism in these processes. To investigate the relationships between appressorial lipolysis and fungal metabolic pathways, C. orbiculare knockout mutants of MFE1, which encodes a peroxisomal multifunctional enzyme, were generated in this study, and the phenotype of the mfe1 mutants was investigated. In contrast to the wild-type strain, which forms melanized appressoria, the mfe1 mutants formed colorless nonmelanized appressoria with abundant LDs, similar to those of pex6 mutants. This indicates that fatty acid β-oxidation in peroxisomes is critical for the appressorial melanization and lipolysis of C. orbiculare. Soraphen A, a specific inhibitor of acetyl-CoA carboxylase, inhibited appressorial lipolysis and melanization, producing phenocopies of the mfe1 mutants. This suggests that the conversion of acetyl-CoA, derived from fatty acid β-oxidation, to malonyl-CoA is required for the activation of lipolysis in appressoria. Surprisingly, we found that genetically blocking PKS1-dependent polyketide synthesis, an initial step in melanin biosynthesis, also impaired appressorial lipolysis. In contrast, genetically or pharmacologically blocking the steps in melanin synthesis downstream from PKS1 did not abolish appressorial lipolysis. These findings indicate that melanin biosynthesis, as well as fatty acid β-oxidation, is involved in the regulation of lipolysis inside fungal infection structures.
黄瓜炭疽病病原菌炭疽菌的分生孢子发育出附着胞，附着胞通过合成黑色素来侵染宿主植物。不成熟的附着胞中含有丰富的脂滴（LDs），但在附着胞成熟过程中这些 LDs 消失，表明附着胞细胞内发生脂解作用。附着胞中的脂解作用和黑色素形成需要过氧化物酶体蛋白 PEX6，这表明过氧化物酶体代谢在这些过程中很重要。为了研究附着胞脂解作用与真菌代谢途径之间的关系，本研究生成了编码过氧化物酶体多功能酶的 C. orbiculare MFE1 敲除突变体，并对 mfe1 突变体的表型进行了研究。与形成黑色素附着胞的野生型菌株不同，mfe1 突变体形成无色非黑色素附着胞，且含有丰富的脂滴，类似于 pex6 突变体。这表明过氧化物体中的脂肪酸β-氧化对 C. orbiculare 附着胞的黑色素形成和脂解作用很关键。 Soraphen A 是乙酰辅酶 A 羧化酶的特异性抑制剂，它抑制附着胞脂解作用和黑色素形成，产生类似于 mfe1 突变体的表型。这表明，来源于脂肪酸β-氧化的乙酰辅酶 A 转化为丙二酰辅酶 A 对于激活附着胞中的脂解作用是必需的。令人惊讶的是，我们发现遗传阻断多酮合酶 PKS1 依赖性聚酮合成（黑色素生物合成的初始步骤）也会损害附着胞的脂解作用。相比之下，遗传或药理学阻断 PKS1 下游的黑色素合成步骤并不会阻止附着胞的脂解作用。这些发现表明，黑色素生物合成以及脂肪酸β-氧化都参与了真菌侵染结构内脂解作用的调节。
