Disruption of abscisic acid signalling constitutively activates Arabidopsis resistance to the necrotrophic fungus Plectosphaerella cucumerina

SÁNCHEZ-VALLET, A.; LÓPEZ, G.; RAMOS, B.; RIVIERE, M-P.; LLORENTE, F.; FERNÁNDEZ, PAULA VIRGINIA; ESTEVEZ,J.M.; GRANT, M.; MOLINA, A.

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Año: 2012

0032-0889

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) and abscisic acid (ABA). 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 hab1-1abi1-2abi2-2 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 defence genes, m any of which are controlled by either the SA, JA or ET pathways. In line with these data, we found that aba1-6 resistance to PcBMM was partially compromised when the SA, JA or ET pathways were disrupted in this mutant. 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 significant differences in their FTIR spectratypes and ur onic acid and cellulose contents. 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.