β-aminobutyric acid-induced resistance in postharvest peach fruit involves interaction between the MAPK cascade and SNARE13 protein in salicylic acid-dependent pathway

The inducer β-aminobutyric acid (BABA) is capable of immune response in various plants. However, the specific mitogen-activated protein kinase (MAPK) cascade involved in BABA-induced resistance (BABA-IR) has not yet been elucidated. Here, peach fruits treated with the BABA exhibited a pattern-triggered immunity (PTI) defense against Rhizopus stolonifer, accompanied by the generation of reactive oxygen species (ROS) and activation of MAPK cascade. Transcriptome sequencing suggested a total of fifteen PpMAPKKK/PpMAPKK/PpMAPK genes involved in BABA-IR in peach fruit. Further qRT-PCR analysis showed that the transcript profiles of PpMAPKKK3, PpMAPKK5 and PpMAPK1 were obviously potentiated. Subsequently, yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), pull-down and in vitro phosphorylation assays were conducted to characterize the complete MAPK cascade (PpMAPKKK3-PpMAPKK5-PpMAPK1) involved in peach fruit. Moreover, the downstream events of MAPK1 include the involvement of SNARE13 and the corresponding NPR1-responsive defense. Single silencing of MAPKKK3, MAPKK5 or MAPK1 and double silencing of MAPKKK3/MAPKK5 or MAPKK5/MAPK1 resulted in enhanced susceptibility to the fungus R. stolonifer in mutants and attenuated salicylic acid (SA)-dependent defense gene expression; in contrast, the homologous or heterologous overexpression of PpSNARE13 in peach fruit or Arabidopsis led to an enhanced SA pool and elevated expression of PR genes. Reciprocally, the ppsnare13cas9 mutants are generally compromised in the priming of SA-dependent resistance. Therefore, the MAPKKK3-MAPKK5-MAPK1 cascade contributes to PTI signal transduction in BABA-elicited peach fruit, by combination with downstream events such as SNARE13, NPR1, and SA-dependent signaling.