אסיף מאגר המחקר החקלאי

PH regulation of ammonia secretion by colletotrichum gloeosporioides and its effect on appressorium formation and pathogenicity

Year:

2010

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Volume :

23

Co-Authors:

Miyara, I., Department of Postharvest Science of Fresh Produce, Bet Dagan 50250, Israel, The Hebrew University of Jerusalem, Robert H. Smith Faculty of Agriculture, Food and Environment, Rehovot 76100, Israel
Shafran, H., Department of Genomics, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Davidzon, M., Department of Postharvest Science of Fresh Produce, Bet Dagan 50250, Israel
Sherman, A., Department of Genomics, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Prusky, D., Department of Postharvest Science of Fresh Produce, Bet Dagan 50250, Israel

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Abstract:

Host-tissue alkalinization via ammonia accumulation is key to Colletotrichum spp. colonization. Using macroarrays carrying C. gloeosporioides cDNAs, we monitored gene expression during the alkalinization process. A set of genes involved in synthesis and catabolism of ammonia accumulation were identified. Expression of NAD+-specific glutamate dehydrogenase (GDH2, encoding ammonia synthesis) and the ammonia exporter AMET were induced at pH 4.0 to 4.5. Conversely, ammonia uptake and transcript activation of the ammonia and glutamate importers (MEP and GLT, respectively) and glutamine synthase (GS1) were higher at pH 6.0 to 7.0. Accumulated ammonia in the wildtype mycelium decreased during ambient alkalinization, concurrent with increased GS1 expression.Δpacl mutants of C. gloeosporioides, which are sensitive to alkaline pH changes, showed upregulation of the acid-expressed GDH2 and downregulation of the alkaline-expressed GSl, resulting in 60% higher ammonia accumulation inside the mycelium. Agdh2 strains of C. gloeosporioides, impaired in ammonia production, showed 85% inhibition in appressorium formation followed by reduced colonization on avocado fruit (Persea americana cv. Fuerte) pericarp, while exogenic ammonia addition restored appressoria formation. Thus the modulation of genes involved in ammonia metabolism and catabolism by C. gloeosporioides is ambient pH-dependent. Aside from its contribution to necrotrophic stages, ammonia accumulation by germinating spores regulates appressorium formation and determines the initiation of biotrophic stages of avocado-fruit colonization by Colletotrichum spp.

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