Cutin monomers, generated by the low levels of constitutively expressed
cutinase, induce high levels of
cutinase that can help pathogenic fungi to penetrate into the host through the cuticle whose major structural
polymer is
cutin. We cloned three highly homologous
cutinase genes, cut1, cut2, and cut3, from Fusarium solani f. pisi (Nectria haematococca). Amino acid sequence deduced from the nucleotide sequence of cut1 and cut2/3 matched with that of the
peptides from
cutinase 1 and
cutinase 2, respectively, isolated from F. solani pisi grown on
cutin as the sole
carbon source. Induction of
beta-glucuronidase gene fused to the promoters of the cutinases integrated into F. solani pisi genome indicates that cut2 is constitutively expressed and induced under
starvation, whereas cut1 is highly induced by
cutin monomers. A palindrome
binding protein (PBP) previously cloned binds only to palindrome 1 of cut1 promoter but not palindrome 1 of cut2/3 which contains two base substitutions. PBP is thought to interfere with the binding of CTF1 alpha, the
transcription factor involved in induction, to cut1 promoter and thus keep cut1 gene repressed until induced by
cutin monomers. Because PBP cannot bind palindrome 1 of cut2, this gene is not repressed. CTF1 alpha does not transactivate cut2 promoter. A new Cys(6)Zn(2) motif-containing
transcription factor, CTF1 beta, that binds palindrome 2 was cloned and sequenced. In yeast, CTF1 beta transactivates cut2 promoter but not cut1 promoter unless its palindrome 1 is mutated, unlike CTF1 alpha which transactivates cut1. Thus, CTF1 beta is involved in the constitutive expression of cut2 that causes production of low levels of
cutin monomers that strongly induce cut1 using CTF1 alpha as the
transcription factor.