Deletion and expression analysis of beta-(1,3)-glucanosyltransferase genes in Neurospora crassa.

Abstract GPI(glycosylphosphatidylinositol)-anchored beta-(1,3)-glucanosyltransferases play an active role in cell wall biosynthesis in fungi. Neurospora crassa has 5 putative beta-(1,3)-glucanosyltransferase genes, namely, gel-1 , gel-2 , gel-3 , gel-4 , and gel-5 , in its genome. Among them, the gel-3 gene is constitutively expressed at the highest level in growing hyphae, whereas gel-1 is expressed at the lowest level. The gel-3 deletion mutant displayed slow growth, while other gel gene disruptants exhibited normal growth. Although no gel gene disruption affected pH sensitivity and fertility, all Δgel mutants were resistant to cell wall degradation enzymes. Micafungin, a beta-(1,3)-glucan synthase inhibitor, induced gel-4 expression in the wild-type and 2 MAP kinase mutants mak-1 and mak-2 strains. In contrast, fludioxonil, an activator of OS-2 MAP kinase, strongly induced the gel-1 gene in the wild-type strain. Its induction was nearly abolished in the os-2 and in the atf-1/asl-1 mutant. These suggested that GEL-3 is a major factor in mycelial growth, while GEL-1 and GEL-4 may play important roles in cell wall remodeling in response to stress conditions or cell wall damage, respectively.