Roles of plant hormones and their interplay in rice immunity.

Plant hormones have been extensively studied for their importance in innate immunity particularly in the dicotyledonous model plant Arabidopsis thaliana. However, only in the last decade, plant hormones were demonstrated to play conserved and divergent roles in fine-tuning immune in rice (Oryza sativa L.), a monocotyledonous model crop plant. Emerging evidence showed that salicylic acid (SA) plays a role in rice basal defense but is differentially required by rice pattern recognition receptor (PRR) and resistance (R) protein-mediated immunity, and its function is likely dependent on the signaling pathway rather than the change of endogenous levels. Jasmonate (JA) plays an important role in rice basal defense against bacterial and fungal infection and may be involved in the SA-mediated resistance. Ethylene (ET) can act as a positive or negative modulator of disease resistance, depending on the pathogen type and environmental conditions. Brassinosteroid (BR) signaling and abscisic acid (ABA) either promote or defend against infection of pathogens with distinct infection/colonization strategies. Auxin and gibberellin (GA) are generally thought of as negative regulators of innate immunity in rice. Moreover, GA interacts antagonistically with JA signaling in rice development and immunity through the DELLA protein as a master regulator of the two hormone pathways. In this review, we summarize the roles of plant hormones in rice immunity and discuss their interplay/crosstalk mechanisms and the complex regulatory network of plant hormone pathways in fine-tuning rice immunity and growth.