PDF(Pubmed)
Abstract：
Hyphal polarized growth in filamentous fungi requires tip-directed secretion, while additional evidence suggests that fungal exocytosis for the hydrolytic enzyme secretion can occur at other sites in hyphae, including the septum. In this study, we analyzed the role of the exocyst complex involved in the secretion in the banana wilt fungal pathogen Fusarium odoratissimum. All eight exocyst components in F. odoratissimum not only localized to the tips ahead of the Spitzenkörper in growing hyphae but also localized to the outer edges of septa in mature hyphae. To further analyze the exocyst in F. odoratissimum, we attempted single gene deletion for all the genes encoding the eight exocyst components and only succeeded in constructing the gene deletion mutants for exo70 and sec5; we suspect that the other 6 exocyst components are encoded by essential genes. Deletion of exo70 or sec5 led to defects in vegetative growth, conidiation, and pathogenicity in F. odoratissimum. Notably, the deletion of exo70 resulted in decreased activities for endoglucosidase, filter paper enzymes, and amylase, while the loss of sec5 only led to a slight reduction in amylase activity. Septum-localized α-amylase (AmyB) was identified as the marker for septum-directed secretion, and we found that Exo70 is essential for the localization of AmyB to septa. Meanwhile the loss of Sec5 did not affect AmyB localization to septa but led to a higher accumulation of AmyB in cytoplasm. This suggested that while Exo70 and Sec5 both take part in the septum-directed secretion, the two play different roles in this process. IMPORTANCE The exocyst complex is a multisubunit tethering complex (MTC) for secretory vesicles at the plasma membrane and contains eight subunits, Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84. While the exocyst complex is well defined in eukaryotes from yeast (Saccharomyces cerevisiae) to humans, the exocyst components in filamentous fungi show different localization patterns in the apical tips of hyphae, which suggests that filamentous fungi have evolved divergent strategies to regulate endomembrane trafficking. In this study, we demonstrated that the exocyst components in Fusarium odoratissimum are localized not only to the tips of growing hyphae but also to the outer edge of the septa in mature hyphae, suggesting that the exocyst complex plays a role in the regulation of septum-directed protein secretion in F. odoratissimum. We further found that Exo70 and Sec5 are required for the septum-directed secretion of α-amylase in F. odoratissimum but with different influences.
摘要：
丝状真菌中的菌丝极化生长需要尖端定向分泌，虽然其他证据表明，真菌对水解酶分泌的胞吐作用可以发生在菌丝的其他部位，包括隔膜.在这项研究中,我们分析了香蕉枯萎病真菌病原体镰刀菌中分泌的外囊复合物的作用。F.odoratissimum中的所有八个外囊成分不仅在生长的菌丝中定位于Spitzenkörper之前的尖端，而且在成熟的菌丝中定位于隔膜的外缘。为了进一步分析奥氏F.ododatissimum的外囊，我们尝试对编码8个外囊成分的所有基因进行单基因缺失，仅成功构建了exo70和sec5的基因缺失突变体；我们怀疑其他6个外囊成分是由必需基因编码的。Exo70或sec5的缺失导致营养生长的缺陷，分生孢子，和致病性。值得注意的是,Exo70的缺失导致内切葡萄糖苷酶的活性降低，滤纸酶，和淀粉酶，而sec5的损失仅导致淀粉酶活性略有降低。中隔定位的α-淀粉酶（AmyB）被确定为中隔定向分泌的标志物，我们发现Exo70对于AmyB定位到隔膜是必不可少的。同时，Sec5的丢失不会影响AmyB在隔片上的定位，但会导致AmyB在细胞质中的更高积累。这表明，虽然Exo70和Sec5都参与了隔膜定向分泌，两者在这个过程中扮演不同的角色。重要性外囊复合物是一种多亚基连接复合物（MTC），用于质膜上的分泌囊泡，包含八个亚基，Sec3、Sec5、Sec6、Sec8、Sec10、Sec15、Exo70和Exo84。虽然在从酵母（酿酒酵母）到人类的真核生物中，外囊复合物是明确的，丝状真菌中的外囊成分在菌丝顶端表现出不同的定位模式，这表明丝状真菌已经进化出不同的策略来调节内膜运输。在这项研究中,我们证明了臭镰刀菌中的外囊成分不仅位于生长菌丝的尖端，而且位于成熟菌丝中隔膜的外缘，这表明外囊复合物在F.odoatissimum中隔膜定向蛋白分泌的调节中起作用。我们进一步发现，Exo70和Sec5是F.odoatissimum中α-淀粉酶的隔膜定向分泌所必需的，但影响不同。
