CONICET | Buscador de Institutos y Recursos Humanos

Plant resistance to necrotrophic fungi is regulated by a complex set of signalling pathways, that includes those mediated by the hormones salicylic acid (SA), ethylene (ET), jasmonic acid (JA), abscisic acid (ABA), auxins and giberellins. The role of ABA in plant resistance remains controversial as positive and negative regulatory functions have been described depending on the plant-pathogen interaction analysed. Here, we show that ABA signalling negatively regulates Arabidopsis thaliana resistance to the necrotrophic fungus Plectosphaerella cucumerina BMM (PcBMM). Arabidopsis plants impaired in ABA biosynthesis, such as aba1-6 mutant, or in ABA signalling, like the quadruple pyr/pyl mutant, were more resistant to PcBMM than wild-type plants. In contrast, the abi1 abi2 hab1 mutant impaired in three phosphatases that negatively regulate ABA signalling displayed an enhanced susceptibility phenotype to this fungus. Comparative transcriptomic analyses of aba1-6 and wild-type plants revealed that ABA pathway negatively regulates defensive genes, many of which are controlled by either the SA, JA or ET pathways. In line with these data, we found that the resistance to PcBMM of aba1-6 mutant was partially compromised in the aba1-6 sid2-1, aba1-6 aos and aba1-6 ein2-1 double mutants, impaired in the SA, JA and ET pathways, respectively. Additionally, in the aba1-6 plants some genes encoding cell wall-related proteins were mis-regulated. Fourier Transform InfraRed (FTIR) spectroscopy and biochemical analyses of cell walls from aba1-6 and wild-type plants revealed that FTIR spectratypes and uronic acid and cellulose contents in aba1-6 differed from those of wild-type plants. All these data suggest that ABA signalling has a complex function in Arabidopsis immunity, negatively regulating SA/JA/ET-mediated resistance to necrotrophic fungi and determining plant cell wall composition.