Foliage inoculation by Burkholderia vietnamiensis CBMB40 antagonizes methyl jasmonate-mediated stress in Eucalyptus grandis

Abstract

Methyl jasmonate (MeJA) is widely used as a model chemical to study hypersensitive responses to biotic stress impacts in plants. Elevated levels of methyl jasmonate induce jasmonate-dependent defense responses, associated with a decline in primary metabolism and enhancement of secondary metabolism of plants. However, there is no information of how stress resistance of plants, and accordingly the sensitivity to exogenous MeJA can be decreased by endophytic plant growth promoting rhizobacteria (PGPR) harboring ACC (1-aminocyclopropane-1-carboxylate) deaminase. In this study, we estimated stress alleviating potential of endophytic PGPR against MeJA-induced plant perturbations through assessing photosynthetic traits and stress volatile emissions. We used mild (5 mM) to severe (20 mM) MeJA and endophytic plant growth promoting rhizobacteria Burkholderia vietnamiensis CBMB40 and studied how MeJA and B. vietnamiensis treatments influenced temporal changes in photosynthetic characteristics and stress volatile emissions. Separate application of MeJA markedly decreased photosynthetic characteristics and increased lipoxygenase pathway (LOX) volatiles, volatile isoprenoids, saturated aldehydes, lightweight oxygenated compounds (LOC), geranyl-geranyl diphosphate pathway (GGDP) volatiles, and benzenoids. However, MeJA-treated leaves inoculated by endophytic bacteria B. vietnamiensis had substantially increased photosynthetic characteristics and decreased emissions of LOX, volatile isoprenoids and other stress volatiles compared with non-inoculated MeJA treatments, especially at later stages of recovery. In addition, analysis of leaf terpenoid contents demonstrated that several mono- and sesquiterpenes were de novo synthesized upon MeJA and B. vietnamiensis applications. This study demonstrates that foliar application of endophytic bacteria B. vietnamiensis can potentially enhance resistance to biotic stresses and contribute to the maintenance of the integrity of plant metabolic activity.

Keywords: Eucalyptus grandis; Isoprene; Methyl jasmonate; Monoterpenes; Photosynthesis; Plant growth promoting rhizobacteria.