Control of polygalacturonase synthesis in Fusarium oxysporum f.sp. radicis lycopersici

Genetic control of polygalacturonase (FG) activity from Fusarium oxysporum f.sp. radicis lycopersici was analyzed on pectin and glucose cultures, One exopolygalacturonase from F. oxysporum f.sp. radicis lycopersici was strongly induced, in stationary culture, when the fungus was grown on apple pectin, while on glucose no extracellular PG activity could be detected. Although SDS-PAGE detected the presence of a putative PG band (66 kDa) in both conditions, specific antibodies obtained against the purified PG only detected it in PG-inducing conditions, that is to say, when apple pectin was used as the carbon source, Northern blot analysis of RNA of two isolates of F. oxysporum f.sp. radicis lycopersici (r(6) and r(2)) confirmed that this regulation of PG synthesis was exerted at the transcriptional level. Only one single mRNA species of around 1400 nucleotides was detected on the cultures containing pectin and was absent in glucose-grown cultures. Southern blot analysis of genomic DNA indicated that pg gene seems to be present in a single copy in the genomes of F. oxysporum f.sp radicis lycopersici r(6) and r(2) and Fusarium oxysporum f.sp. lycopersici, showing similar hybridization patterns in all species. The partial sequence of this pg gene from F. oxysporum f.sp, radicis lycopersici r(6), which is also reported, showed high similarity to diverse PGs already reported, Exopolygalacturonase of F. oxysporum f.sp. radicis lycopersici r(6) is heavily glycosylated; its deglycosylated form had a molecular mass of 50 kDa.