Colonization of Piriformospora indica enhances insect herbivore resistance of rice plants through jasmonic acid- and antioxidant-mediated defense mechanisms

Piriformospora indica (P. indica) is a mutualistic endophyte that colonizes plant roots. In this study, effects of P. indica on rice resistance against rice leaffolder (Cnaphalocrocis medinalis Guenee) were investigated. Growth inhibition and leaf injury caused by leaffolder larvae infestation in P. indica-colonized rice was significantly alleviated. Moreover, growth retardation was observed in larvae which fed on P. indica-colonized plants. JA-Ile levels and trypsin inhibitor activities in leaf tissues of P. indica-colonized plants were higher than those in noncolonized plants under leaffolder-infested conditions. P. indica effects on increasing trypsin inhibitor expression and reducing larval growth were repressed by aspirin. JA signaling drives P. indica-enhanced insect resistance in rice, and trypsin inhibitors might be candidates involved in this mechanism. Changes in antioxidant enzyme activities and malondialdehyde levels in P. indica-inoculated plants were observed, and it was demonstrated that oxidative stress induced by insect infestation could be reduced in P. indica-colonized plants.