A cis-acting sequence homologous to the yeast filamentation and invasion response element regulates expression of a pectinase gene from the bean pathogen Colletotrichum lindemuthianum.

Abstract

Phytopathogenic fungi secrete hydrolytic enzymes that degrade plant cell walls, notably pectinases. The signaling pathway(s) that control pectinase gene expression are currently unknown in filamentous fungi. Recently, the green fluorescent protein coding sequence was used as a reporter gene to study the expression of CLPG2, a gene encoding an endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum. CLPG2 is transcriptionally induced by pectin in the axenic culture of the fungus and during formation of the appressorium, an infection structure specialized in plant tissue penetration. In the present study, promoter deletion and mutagenesis, as well as gel shift mobility assays, allowed for the first time identification of cis-acting elements that bind protein factors and are essential for the regulation of a pectinase gene. We found that two different adjacent DNA motifs are combined to form an active element that shows a strong sequence homology with the yeast filamentation and invasion response element. The same element is required for the transcriptional activation of CLPG2 by pectin and during appressorium development. This study strongly suggests that the control of virulence genes of fungal plant pathogens, such as pectinases, involves the formation of a complex of transcriptional activators similar to those regulating the invasive growth in yeast.