Functional analysis of the β2 -tubulin gene of Fusarium graminearum and the β-tubulin gene of Botrytis cinerea by homologous replacement.

Background: Resistance to carbendazim and other benzimidazole fungicides in Botrytis cinerea and most other fungi is usually conferred by one or several allelic mutations in the β-tubulin. Carbendazim resistance in Fusarium graminearum, however, differs from that in B. cinerea and other fungi in that F. graminearum has two β-tubulins (Fgtub1 and Fgtub2) rather than one, and the resistance is conferred by mutations in the β2 -tubulin. In a previous study, the β1 -tubulin of F. graminearum (Fgtub1) was replaced with the β-tubulin of B. cinerea conferring carbendazim resistance (BctubE198A). The transformants were sensitive to carbendazim.

Results: BctubE198A was successfully transferred into the β2 -tubulin locus of F. graminearum (Fgtub2) via homologous replacement. The mutants were still sensitive to carbendazim. Furthermore, Fgtub2 of the mutant 20C1 (Fgtub1 had been replaced with BctubE198A) and Fgtub1 of the mutant 20D10 (Fgtub2 had been replaced with BctubE198A) were deleted. Surprisingly, the mutants were also sensitive to carbendazim. Meanwhile, the biological characteristics of all the mutants were determined.

Conclusion: The B. cinerea β-tubulin (Bctub) could complement the function of the two F. graminearum β-tubulins even when both were deleted. Expression of the β-tubulin conferring carbendazim resistance differs between pathogenic fungi.