Authors:Zsuzsanna Kiss, Judit Dobránszki, Ildikó Hudák, Zsuzsanna Birkó, G. Vargha, and S. Biró
The Gram-positive soil-borne streptomycetes exhibit a complex life cycle that is controlled by extracellular regulatory molecules. One interesting autoregulator is the protein factor C, originally isolated from the culture fluid of
45H. Southern hybridizations and database searches revealed that although homologues of factor C are not present in most
strains, an exception is the plant pathogenic
, which causes common scab disease on potato. In
and related strains pathogenicity involves a large pathogenicity island that carries thaxtomin biosynthetic genes, the
necrogenic factor and other putative virulence genes. Extracellular enzymes, including extracellular esterases, that attack the surface of the tubers and disintegrate the external protective layer are also known to be involved in pathogenicity. In
45H, factor C coordinates the expression of many secreted hydrolases. To find out whether esterase is also regulated by factor C, we made a factor C null mutant of strain 45H. The mutant showed a bald phenotype and was impaired in pathogenicity and esterase activity. This is a first indication that extracellular regulatory factors may play a role in the development of potato scab.