Priming of defense-related genes in Brassica oleracea var. capitata using concentrated metabolites produced by Rhizobium tropici CIAT 899.

To verify the potential of metabolites extracted from Rhizobium tropici to trigger the priming of defense responses in cruciferous plants, we analyzed the expression of defense-related genes by qRT-PCR. Brassica oleracea var. capitata, susceptible to Xanthomonas campestris pv. campestris, were grown in greenhouse conditions. At 18 days after sowing, plants were inoculated with 1 mL of 1% concentrated metabolites produced by R. tropici (CM-RT) in the root. In a second experiment, leaves were sprayed with 1 mL of a solution containing 1% CM-RT. Aerial and root tissue were collected separately at 0 (non-treated control condition), 24, and 48 h after application, submitted to RNA extraction and gene expression analysis by qRT-PCR. The results showed that, after root treatment with CM-RT, most evaluated genes were upregulated at 24 h after application and downregulated at 48 h after application in roots, while in leaves, genes were downregulated both at 24 and 48 h after application. On the other hand, leaf treatment with CM-RT showed that most evaluated genes in leaves and roots were upregulated at 24 and 48 h after application. These results indicate that the effect of CM-RT applied in roots seems restricted to the applied region and is not sustained, while the application in leaves results in a more systemic response and maintenance of the effect of CM-RT for a longer period. The results obtained in this study emphasize the biotechnological potential of using metabolites of R. tropici as an elicitor of active defense responses in plants.