A GAL4-like Protein Is Involved in the Switch between Biotrophic and Necrotrophic Phases of the Infection Process of Colletotrichum lindemuthianum on Common Bean

Abstract

Random insertional mutagenesis was conducted with the hemibiotrophic fungus Colletotrichum lindemuthianum , causal agent of common bean anthracnose. Nine mutants that were altered in their infection process on the host plant were generated. One of these, H433 is a nonpathogenic mutant able to induce necrotic spots on infected leaves rapidly. These spots are similar to those observed during the hypersensitive reaction. Cytological observations showed that the development of the mutant H433 is stopped at the switch between the biotrophic and the necrotrophic phases. This mutant carries two independent insertions of the transforming plasmid pAN7-1. Complementation studies using the wild-type genomic regions corresponding to the two insertions showed that one is responsible for the H433 phenotype. Sequencing analysis identified a single open reading frame that encoded a putative transcriptional activator belonging to the fungal zinc cluster (Zn[II] 2 Cys 6 ) family. The corresponding gene was designated CLTA1 (for C. lindemuthianum transcriptional activator 1). Expression studies showed that CLTA1 is expressed in low amounts during in vitro culture. Targeted disrupted strains were generated, and they exhibited the same phenotype as the original mutant H433. Complementation of these disrupted strains by the CLTA1 gene led to full restoration of pathogenicity. This study demonstrates that CLTA1 is both a pathogenicity gene and a regulatory gene involved in the switch between biotrophy and necrotrophy of the infection process of a hemibiotrophic fungus.

Plant infection and the establishment of fungal biotrophy

“…Host walls break down because of the secretion of large amounts of cell-wall-degrading enzymes by the secondary hyphae (arrows). disrupted gene, CLTA1, which appears to be a transcriptional activator belonging to the zinc cluster family [18]. In the cucurbit pathogen Colletotrichum magna, a large-scale screening of REMI mutants resulted in many isolates that caused symptomless infections [13].…”

Overexpression of a Novel Biotrophy-Specific Colletotrichum truncatum Effector, CtNUDIX, in Hemibiotrophic Fungal Phytopathogens Causes Incompatibility with Their Host Plants

“…To date, four genes have been shown to regulate the BNS: CLTA1 and CLNR1 (Colletotrichum lindemuthianum [3,4]), CPR1 (Colletotrichum graminicola [5]), and a gene encoding a putative importin-␤2 protein (Colletotrichum higginsianum [6]). The CLTA1 and CLNR1 genes encode a GAL4-like transcriptional activator belonging to the fungal zinc cluster (Zn 2 2ϩ Cys 6 ) family and an AREA/NIT2-like global nitrogen regulator, respectively, whereas the CPR1 gene encodes a subunit of the signal peptidase complex.…”

Sequence analysis and expression pattern ofMGTA1gene in rice blast pathogenMagnaporthe grisea

“…In these homologues, a predicted protein FG00573.1 from Gibberella zeae had 54% identity to the protein Mgta1p and 56% identity to Clta1p (Fig.3). G. zeae does not form appressorium for plant penetration, and the CLTA1 null mutants of C. lindemuthianum can form appressoria normally (Dufresne et al, 2000), so MGTA1 is possibly involved in other processes. It will be interesting to determine the function of MGTA1, FG00573.1 and their homologous genes fungal pathogens.…”

“…In this study, we isolated MGTA1, a novel gene homologous to CLTA1 involved in the post-penetration processes of C. lindemuthianum (Dufresne et al, 2000). (Dufresne et al, 2000), MGTA1 gene is expressed in several phases of the M. grisea infection cycle: tip hypha, conidium and mature appressorium. While in infectious hypha, eGFP fluorescence cannot be detected.…”

“…A null mutant of CLTA1 gene stops at biotrophic phase and loses its pathogenicity on common bean. In infected cells, mutants can form primary intracellular hyphae but cannot differentiate infectious secondary hyphae (Dufresne et al, 2000).…”