אסיף מאגר המחקר החקלאי

Effect of ammonia production by Colletotrichum gloeosporioides on pelB activation, pectate lyase secretion, and fruit pathogenicity

Year:

2006

Source of publication :

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Volume :

72

Co-Authors:

Kramer-Haimovich, H., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Servi, E., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Katan, T., Department of Plant Pathology, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Rollins, J., Department of Plant Pathology, University of Florida, Gainesville, FL 32611, United States
Okon, Y., Department of Plant Pathology and Microbiology, Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot 76100, Israel
Prusky, D., Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel

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Abstract:

The accumulation of ammonia and associated tissue alkalinization predispose avocado fruit to attack by Colletotrichum gloeosporioides. Secretion of ammonia by C. gloeosporioides in the presence of KNO3 was induced by decreasing the pH from 7.0 to 4.0. When the fungus was grown at pH 4.0 or 6.0 in the absence of a nitrogen source, ammonia did not accumulate, and neither pelB (encoding pectate lyase) transcription nor pectate lyase secretion was detected. Under these nitrogen starvation conditions, only transcriptional activation of areA, which encodes the global nitrogen regulator, was detected. pelB transcription and pectate lyase secretion were both detected when C. gloeosporioides was grown at pH 6.0 in the presence of ammonia accumulated from different nitrogen sources. The early accumulation of ammonia induced early pelB expression and pectate lyase secretion. As the external pH increased from 4.0 to 6.0, transcripts of pac1, the C. gloeosporioides pacC homolog, also could be detected. Nit mutants of C. gloeosporioides, which cannot utilize KNO 3 as a nitrogen source, did not secrete ammonia, alkalinize the medium, or secrete pectate lyase. If Nit mutants were grown at pH 6.0 in the presence of glutamate, then pectate lyase secretion was induced. Infiltration of 0.1 M ammonium hydroxide at pH 10 into ripening avocado fruits enhanced the activation of quiescent infection and symptom development by C. gloeosporioides. These results suggest that ambient pH alkalinization resulting from ammonia accumulation and the availability of ammonia as a nitrogen source independently regulate pelB expression, pectate lyase secretion, and virulence of C. gloeosporioides. These data suggest that alkalinization during C. gloeosporioides infection is important for its transformation from the quiescent biotrophic stage to the necrotrophic stage of fungal colonization in the fruit host. Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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