Functional Roles of α 1 -, α 2 -, β 1 -, and β 2 -Tubulins in Vegetative Growth, Microtubule Assembly, and Sexual Reproduction of Fusarium graminearum

The plant pathogen Fusarium graminearum contains two α-tubulin isotypes (α and α ) and two β-tubulin isotypes (β and β ). The functional roles of these tubulins in microtubule assembly are not clear. Previous studies reported that α - and β -tubulin deletion mutants showed severe growth defects and hypersensitivity to carbendazim, which have not been well explained. Here, we investigated the interaction between α- and β-tubulin of F. graminearum. Colocalization experiments demonstrated that β - and β -tubulin are colocalized. Coimmunoprecipitation experiments suggested that β -tubulin binds to both α - and α -tubulin and that β -tubulin can also bind to α - or α -tubulin. Interestingly, deletion of α -tubulin increased the interaction between β -tubulin and α -tubulin. Microtubule observation assays showed that deletion of α -tubulin completely disrupted β -tubulin-containing microtubules and significantly decreased β -tubulin-containing microtubules. Deletion of α -, β -, or β -tubulin had no obvious effect on the microtubule cytoskeleton. However, microtubules in α - and β -tubulin deletion mutants were easily depolymerized in the presence of carbendazim. The sexual reproduction assay indicates that α - and β -tubulin deletion mutants could not produce asci and ascospores. These results implied that α -tubulin may be essential for the microtubule cytoskeleton. However, our Δα -2×α mutant (α -tubulin deletion mutant containing two copies of α -tubulin) exhibited normal microtubule network, growth, and sexual reproduction. Interestingly, the Δα -2×α mutant was still hypersensitive to carbendazim. In addition, both β -tubulin and β -tubulin were found to bind the mitochondrial outer membrane voltage-dependent anion channel (VDAC), indicating that they could regulate the function of VDAC. In this study, we found that F. graminearum contains four different α-/β-tubulin heterodimers (α -/β -, α -/β -, α -/β -, and α -/β -tubulin heterodimers), and they assemble together into a single microtubule. Moreover, α - and α -tubulins are functionally interchangeable in microtubule assembly, vegetative growth, and sexual reproduction. These results provide more insights into the functional roles of different tubulins of F. graminearum, which could be helpful for purification of tubulin heterodimers and development of new tubulin-binding agents.