BIG Regulates Stomatal Immunity and Jasmonate Production in Arabidopsis.

Plants have evolved an array of responses that provide them with protection from attack by microorganisms and other predators. Many of these mechanisms depend upon interactions between the plant hormones jasmonate (JA) and ethylene (ET). However, the molecular basis of these interactions is insufficiently understood. Gene expression and physiological assays with mutants were performed to investigate the role of Arabidopsis BIG gene in stress responses. BIG transcription is downregulated by methyl JA (MeJA), necrotrophic infection or mechanical injury. BIG deficiency promotes JA-dependent gene induction, increases JA production but restricts the accumulation of both ET and salicylic acid. JA-induced anthocyanin accumulation and chlorophyll degradation are enhanced and stomatal immunity is impaired by BIG disruption. Bacteria- and lipopolysaccaride (LPS)-induced stomatal closure is reduced in BIG gene mutants, which are hyper-susceptible to microbial pathogens with different lifestyles, but these mutants are less attractive to phytophagous insects. Our results indicate that BIG negatively and positively regulate the MYC2 and ERF1 arms of the JA signalling pathway. BIG warrants recognition as a new and distinct regulator that regulates JA responses, the synergistic interactions of JA and ET, and other hormonal interactions that reconcile the growth and defense dilemma in Arabidopsis.