Biocontrol agent Pythium oligandrum induces defense-related gene expression and suppresses bacterial seedling rot caused by Burkholderia glumae in rice

Pythium oligandrum (PO) has the ability to activate defense-related gene expression and induce resistance against pathogens in dicot plants such as sugar beet, tomato, potato and Arabidopsis thaliana. To elucidate the ability of PO to activate the defense reaction in rice, we studied the induction of defense gene expression and the induced resistance to a bacterial pathogen, Burkholderia glumae, in PO-treated rice seeds. Treatment of rice seeds with oospore suspension of PO after inoculation with B. glumae reduced the severity of seedling rot. The expression of a defense-related gene, OsPR10a/PBZ1, a marker for disease resistance in rice, was induced in both rice seeds and seedlings treated with an oospore suspension of PO. In rice seedlings treated with the PO oospore suspension, the expression of jasmonic acid (JA)-responsive OsPR10b and OsPR6 was also induced. A global gene expression analysis of the roots treated with the cell wall protein (CWP) fraction extracted from PO, a resistance elicitor, indicated that CWP enhanced expression of genes encoding lipoxygenase and allene oxide synthase, key enzymes for JA synthesis, in addition to OsPR10a/PBZ1, OsPR10b and OsPR6. However, salicylic acid-responsive genes were not upregulated. These findings suggest that PO activates a JA-signaling-mediated defense reaction and induces resistance in rice against infection by B. glumae.