Figure 2.

Biotic stress-related signalling pathways associated with acyl-CoA-binding proteins (ACBPs) in plants. Upon pathogen infection, the overexpression of Class III AtACBP3 in transgenic Arabidopsis thaliana led to constitutive activation of pathogenesis-related (PR) genes including PR1, PR2 and PR5, elevated H₂O₂ production and eventually cell death [121]. AtACBP3 plays a distinct role in the plant defence response against necrotrophic and biotrophic pathogens as transgenic Arabidopsis AtACBP3-overexpressors (OEs) were protected against the biotrophic pathogen (Pseudomonas syringae pv tomato DC3000) but not the necrotrophic pathogen (Botrytis cinerea) [121]. In wild-type Arabidopsis, the expression of Class IV AtACBP4 and AtEBP encoding a protein interactor of AtACBP4 were reported to be induced by B. cinerea infection, and ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and methyl jasmonate (MeJA) treatments, suggesting that AtACBP4 and AtEBP are mediated by ethylene and/or JA signalling [74]. Rice Class III OsACBP5 protects transgenic Arabidopsis and rice plants against hemibiotrophs and biotrophs via NPR1-dependent SA signalling, and necrotrophs by JA signalling [93,127]. The OsACBP5 5′-flanking region contains W-boxes which were verified in pathogen-responsiveness of OsACBP5 [93]. Proteomic studies showed that eleven biotic stress-related proteins were upregulated by Rhizoctonia solani infection in transgenic Arabidopsis OsACBP5-OEs [127]. Grape Class III VvACBP conferred resistance to P. syringae and Colletotrichum higginsianum in transgenic Arabidopsis, possibly through the NPR1-mediated pathway following induction of PDF1.2, the gene encoding plant defensin [100]. Orange boxes represent the named ACBPs involved in the pathogen response. White boxes indicate the molecular events that occur along the signalling pathway. Black arrows denote the flow of signalling events. ACBP, acyl-CoA-binding protein; EBP, ETHYLENE-RESPONSIVE BINDING PROTEIN; JA, jasmonic acid; NPR1, NONEXPRESSOR OF PR-1; PR, pathogenesis-related; SA, salicylic acid.