Fungal and plant gene expression during synchronized infection of tomato leaves by Botrytis cinerea

An inoculation procedure was developed to obtain efficient and synchronous infection on detached tomato leaves by Botrytis cinerea. In spray-inoculated leaves incubated at 20 degrees C, the infection process consisted of three phases: the formation of primary necrotic lesions (until 20 hpi), a quiescent phase (20-72 hpi), and the expansion of a proportion of the primary lesions (from 72 hpi onwards), resulting in full tissue maceration. At 4 degrees C, the infection progressed slowly but steadily without inducing necrotic responses in the host. The actin and beta-tubulin genes of B. cinerea were cloned, characterized and used as probes on blots containing RNAs from leaves at various stages of the infection. The genes displayed a similar expression pattern throughout the infection and the hybridization signal reflected the amount of fungal biomass. The actin mRNA accumulated to higher levels than the beta-tubulin mRNA. Tomato PR protein mRNAs (chitinase, beta-1,3-glucanase and PR-1) were induced during the infection, albeit with different kinetics and to different levels. At 20 degrees C, beta-1,3-glucanase and PR-1 mRNAs were induced more rapidly than chitinase mRNAs. At 4 degrees C, mRNAs encoding extracellular beta-1,3-glucanase and intracellular, as well as extracellular chitinase were hardly induced.