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 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 tried to do single gene deletion for all the genes encoding the eight exocyst components and only succeed to construct 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. Septa-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 while Exo70 and Sec5 both take part in the septum-directed secretion, the two conduct 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 to humans, the exocyst components in filamentous fungi show different localization patterns in the apical tips of hyphae that suggests filamentous fungi have evolved divergent strategies to regulate endomembrane trafficking. In this study, we demonstrated that the exocyst components in
Fusarium odoratissimum
are not only localized 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 influence.