Control of plant diseases by chitinase expressed from cloned DNA in Escherichia coli

A DNA fragment carrying the chiA gene from Serratia marcescens was subcloned into the plasmid pBR322. The resulting plasmid, pCHIA, includes a 2-kilobase-pair segment upstream of the chiA gene and presumably carries the gene regulatory elements. To obtain high levels of chitinase expression, we introduced the leftward operator promoter of bacteriophage λ, oLpL, upstream of the chiA gene. The resulting plasmid, pLCHIA was introduced into cells of Escherichia coli. High levels of chitinase were produced and secreted following induction, and the enzyme was partially purified. When Sclerotium rolfsii was sprayed with partially purified chitinase produced by the cloned gene described above, rapid and extensive bursting of the hyphal tips was observed. This chitinase preparation was found to be effective in reduction of disease incidence caused by S. rolfsii in beans and Rhizoctonia solani in cotton under greenhouse conditions (62% disease reduction in both diseases). A similar effect was obtained when we used viable cells of E. coli containing the plasmid pLCHIA. However, E. coli carrying the plasmid lacking the pL promotor did not have any effect. These results suggest a role for chitinase in biological control of plant pathogenic fungi.