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Applied and Environmental Microbiology, June 2003, p. 3258-3262, Vol. 69, No. 6
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.6.3258-3262.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

External pH and Nitrogen Source Affect Secretion of Pectate Lyase by Colletotrichum gloeosporioides

Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250,¹ Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100,² Department of Molecular Biology, Hebrew University, Medical School, Jerusalem 91120, Israel,⁴ Department of Plant Pathology, University of Florida, Gainesville, Florida 32611³

Received 28 August 2002/ Accepted 6 March 2003

Accumulation of ammonia and associated tissue alkalinization predispose fruit to attack by Colletotrichumgloeosporioides. As the external pH increases from 4.0 to 6.0, pectate lyase (PL) and other extracellular proteins are secreted and accumulate. At pH 4.0 neither pelB (encoding PL) transcription nor PL secretion were detected; however, they were detected as the pH increased. Nitrogen assimilation also was required for PL secretion at pH 6.0. Both inorganic and organic nitrogen sources enhanced PL secretion at pH 6.0, but neither was sufficient for PL secretion at pH 4.0. Sequence analysis of the 5' upstream region of the pelB promoter revealed nine putative consensus binding sites for the Aspergillus transcription factor PacC. Consistent with this result, the transcript levels of pac1 (the C. gloeosporioides pacC homologue) and pelB increased in parallel as a function of pH. Our results suggest that the ambient pH and the nitrogen source are independent regulatory factors for processes linked to PL secretion and virulence of C. gloeosporioides.

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