Abstract
In fungi a genetic system ensures that enzymes are secreted mainly at ambient pH values corresponding to their optima of activity. Although a great deal of information has been obtained concerning this environmental response, there is a lack of studies involving phytopathogenic, endophytic and entomopathogenic fungi as well as different aspects of fungus-host interactions. This study compares in a plate-clearing assays, the effect of ambient pH in the secretion of amylase, cellulase, lipase, pectinase and protease by endophytic, phytopathogenic, and entomopathogenic isolates belonging to several species of Colletotrichum. All enzymes were secreted in a pH-dependent manner by all isolates. Endophytes and pathogens showed distinct patterns of protease secretion, with optima at alkaline and acid growth conditions, respectively. In liquid medium, a Pi-repressible acid phosphatase of an endophytic isolate responded to ambient pH, having a 14-fold increase in secreted specific activity at acid pH, as compared to alkaline pH. Furthermore, part of a Colletotrichum pacC homologue gene, coding for a transcriptional factor responsible for pH-regulated gene expression, was cloned. Ambient pH seems to be a general factor controlling enzyme secretion in fungus-host interactions through a conserved genetic circuit.
Highlights
During fungal infection a range of hydrolytic enzymes is secreted to help promoting host colonization
This study compares in a plate-clearing assays, the effect of ambient pH in the secretion of amylase, cellulase, lipase, pectinase and protease by endophytic, phytopathogenic, and entomopathogenic isolates belonging to several species of Colletotrichum
Genes palA, B, C, F, H, and I are components of a transduction pathway that senses ambient pH and activates the PacC protein. This genetic system seems to be well conserved among fungi (Penãlva & Arst, 2002), but only very recently a pacC homologue has been identified in a phytopathogen, the filamentous fungus Sclerotinia sclerotiorum (Rollins & Dickman, 2001)
Summary
During fungal infection a range of hydrolytic enzymes is secreted to help promoting host colonization. Depending of the ecological niche occupied by each fungus, a particular set of enzymes, mainly composed of proteases and carbohydrases, are displayed to degrade specific tissues and scavenge for nutrient resources (Yakoby et al, 2000). Because these enzymes work outside the fungal cell, activity as well as the mechanisms that control synthesis and secretion are under the influence of several environmental factors such as ambient pH (Caddick et al, 1986; Maccheroni Jr. et al, 1995). Genes palA, B, C, F, H, and I are components of a transduction pathway that senses ambient pH and activates the PacC protein. This genetic system seems to be well conserved among fungi (Penãlva & Arst, 2002), but only very recently a pacC homologue has been identified in a phytopathogen, the filamentous fungus Sclerotinia sclerotiorum (Rollins & Dickman, 2001)
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