Botrytis cinerea endo-ß-1,4-glucanase Cel5A is expressed during infection but is not required for pathogenesis

The cel5A gene, coding for an extracellular endo-ß-1,4-glucanase, has been cloned from the phytopathogenic fungus Botrytis cinerea. The gene contains only one 62-bp intron and encodes a putative protein of 424 amino acids with a signal peptide, a family-5 glycosyl hydrolase domain, and a serine-threonine-rich domain of unknown function. The levels of cel5A transcript and extracellular ß-1,4-glucanase activity were regulated by the carbon source in the same way: both were induced by carboxymethylcellulose and repressed by glucose. The cel5A mRNA could also be detected during the infection of tomato leaves by B. cinerea. Disruption of cel5A results in a strain with identical virulence as the wild-type on tomato leaves or gerbera petals, with no significant reduction in the extracellular ß-1,4-glucanase activity, and with similar growth rate with carboxymethylcellulose or Avicel as the only carbon sources.