Ment, D., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Alkan, N., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Luria, N., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Bi, F.-C., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Reuveni, E., Department of Plant Sciences, Weizmann Institute of Science, Rehovot, Israel
Fluhr, R., Department of Plant Sciences, Weizmann Institute of Science, Rehovot, Israel
Prusky, D., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel

Gene expression regulation by pH in filamentous fungi and yeasts is controlled by the PACC/RIM101 transcription factor. In Colletotrichum gloeosporioides, PACC is known to act as positive regulator of alkaline-expressed genes, and this regulation was shown to contribute to fungal pathogenicity. PACC is also a negative regulator of acid-expressed genes, however; the mechanism of downregulation of acidexpressed genes by PACC and their contribution to C. gloeosporioides pathogenicity is not well understood. RNA sequencing data analysis was employed to demonstrate that PACC transcription factor binding sites (TFBS) are significantly overrepresented in the promoter of PACC-upregulated, alkaline-expressed genes. In contrast, they are not overrepresented in the PACC-downregulated, acid-expressed genes. Instead, acid-expressed genes showed overrepresentation of AREB GATA TFBS in C. gloeosporioides and in homologs of five other ascomycetes genomes. The areB promoter contains PACC TFBS; its transcript was upregulated at pH 7 and repressed in ΔpacC. Furthermore, acid-expressed genes were found to be constitutively upregulated in ΔareB during alkalizing conditions. The areB mutants showed significantly reduced ammonia secretion and pathogenicity on tomato fruit. Present results indicate that PACC activates areB expression, thereby conditionally repressing acid-expressed genes and contributing critically to C. gloeosporioides pathogenicity. © 2015 The American Phytopathological Society.