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Applied and Environmental Microbiology, January 2001, p. 75-81, Vol. 67, No. 1
Department of Plant Pathology, University of
Nebraska, Lincoln, Nebraska 68583
Received 11 February 2000/Accepted 4 October 2000
Sclerotinia sclerotiorum acidifies its ambient
environment by producing oxalic acid. This production of oxalic acid
during plant infection has been implicated as a primary determinant of pathogenicity in this and other phytopathogenic fungi. We found that
ambient pH conditions affect multiple processes in S. sclerotiorum. Exposure to increasing alkaline ambient pH
increased the oxalic acid accumulation independent of carbon source,
sclerotial development was favored by acidic ambient pH conditions but
inhibited by neutral ambient pH, and transcripts encoding the
endopolygalacturonase gene pg1 accumulated maximally under
acidic culture conditions. We cloned a putative transcription
factor-encoding gene, pac1, that may participate in a
molecular signaling pathway for regulating gene expression in response
to ambient pH. The three zinc finger domains of the predicted Pac1
protein are similar in sequence and organization to the zinc finger
domains of the A. nidulans pH-responsive transcription
factor PacC. The promoter of pac1 contains eight PacC
consensus binding sites, suggesting that this gene, like its homologs,
is autoregulated. Consistent with this suggestion, the accumulation of
pac1 transcripts paralleled increases in ambient pH. Pac1
was determined to be a functional homolog of PacC by complementation of
an A. nidulans pacC-null strain with pac1. Our
results suggest that ambient pH is a regulatory cue for processes
linked to pathogenicity, development, and virulence and that these
processes may be under the molecular regulation of a conserved
pH-dependent signaling pathway analogous to that in the nonpathogenic
fungus A. nidulans.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.1.75-81.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
pH Signaling in Sclerotinia
sclerotiorum: Identification of a pacC/RIM1 Homolog
and
*
Corresponding author. Mailing address: Department of
Plant Pathology, 406 Plant Sciences Hall, University of Nebraska,
Lincoln, NE 68583-0722. Phone: (402) 472-2849. Fax: (402) 472-2853. E-mail: mdickman{at}unlnotes.unl.edu.
Present address: Department of Plant Pathology, University of
Florida, Gainesville, FL 32611-0680.
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