A role for Penicillium rubens strain 212 xylanolytic system in biocontrol of Fusarium wilt disease in tomato plants

Penicillium rubens strain 212 (PO212) is an effective inducer of resistance mechanisms in tomato plants against Fusarium oxysporum f.sp. lycopersici. During the interaction of PO212 with the plant, different classes of molecules may act as elicitors such as certain secreted endo-xylanases. The aim of this work was to elucidate the possible role of the xylanolytic system of PO212 in its biocontrol activity. We identified potential genes coding for xylanases (xlnA, xlnE, xylP), ss-xylosidase (xlnD) and their transcriptional regulators (xlnR and araR) in PO212, and evaluated their transcriptional patterns in response to tomato root extracts or synthetic medium containing xylan as main carbon source. For this work we compared data from biocontrol strain PO212 with those of two strains of Penicillium, P. rubens S27, and P. chrysogenum IPLA33001, lacking the biocontrol efficacy. Time-course experiments showed the effect of these carbon sources on the expression rates of xylanase genes. To achieve a strong reduction in expression of xylanolytic genes, we generated a null allele of XlnR, as the specific regulator of the xylanase pathway. Absence of XlnR function prevented growth of PO212 on media containing xylan as main carbon source and consequently, expression levels of xylanases were downregulated. The relationship of the xlnR gene regulated pathway to the efficacy of PO212 as a biological control agent was evaluated. Null xlnR strains did not reduce either disease severity or incidence as wild-type PO212 does. Thus, there is a relationship between a correct expression of xylanolytic system and the capability of these enzymes as effective elicitors to trigger of plant defense systems in tomato plants against F. oxysporum f.sp. lycopersici.