Disruption of Abscisic Acid Signaling Constitutively Activates Arabidopsis Resistance to the Necrotrophic FungusPlectosphaerella cucumerina   

Abstract

Plant resistance to necrotrophic fungi is regulated by a complex set of signaling 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 analyzed. Here, we show that ABA signaling negatively regulates Arabidopsis (Arabidopsis thaliana) resistance to the necrotrophic fungus Plectosphaerella cucumerina. Arabidopsis plants impaired in ABA biosynthesis, such as the aba1-6 mutant, or in ABA signaling, like the quadruple pyr/pyl mutant (pyr1pyl1pyl2pyl4), were more resistant to P. cucumerina than wild-type plants. In contrast, the hab1-1abi1-2abi2-2 mutant impaired in three phosphatases that negatively regulate ABA signaling displayed an enhanced susceptibility phenotype to this fungus. Comparative transcriptomic analyses of aba1-6 and wild-type plants revealed that the ABA pathway negatively regulates defense genes, many of which are controlled by the SA, JA, or ET pathway. In line with these data, we found that aba1-6 resistance to P. cucumerina was partially compromised when the SA, JA, or ET pathway was disrupted in this mutant. Additionally, in the aba1-6 plants, some genes encoding cell wall-related proteins were misregulated. Fourier transform infrared spectroscopy and biochemical analyses of cell walls from aba1-6 and wild-type plants revealed significant differences in their Fourier transform infrared spectratypes and uronic acid and cellulose contents. All these data suggest that ABA signaling has a complex function in Arabidopsis basal resistance, negatively regulating SA/JA/ETmediated resistance to necrotrophic fungi.

Machine Learning Approaches Distinguish Multiple Stress Conditions using Stress-Responsive Genes and Identify Candidate Genes for Broad Resistance in Rice

“…Thus, it was proposed that plants prioritize abiotic stress tolerance over the biotic stress response, with ABA as the molecular switch between the two responses to minimize the damage (Lee and Luan, 2012). Recently, however, contrary studies where biotic stress takes precedence have been reported (Kim et al, 2011;Mang et al, 2012;Sánchez-Vallet et al, 2012). Thus, in light of these recent developments, which revealed a rather complicated picture of multiple stress responses, we embarked on the identification of DEGs in abiotic and biotic stress environments separately and performed comparative analysis of the shared stress-responsive genes, which would provide vital clues on the causative factors behind the cross talk resulting in the observed synergistic and antagonistic regulation of known abiotic and biotic stress response pathways.…”

Spore Density Determines Infection Strategy by the Plant Pathogenic Fungus Plectosphaerella cucumerina

“…S8). To date, previous studies of the Arabidopsis-P. cucumerina interaction employed different inoculation methods, which might explain the controversy about the contribution of SA-and ABA-dependent defense against P. cucumerina (Ton and Mauch-Mani, 2004;Sánchez-Vallet et al, 2012;Gamir et al, 2014). Therefore, we urge extra caution when using the Arabidopsis-P. cucumerina pathosystem as a model for studying interactions between plants and necrotrophic fungi.…”

“…However, among all these studies, there is increasing controversy about the exact signaling pathways and defense responses contributing to plant resistance against P. cucumerina. While it is clear that JA and ethylene contribute to basal resistance against the fungus, the exact roles of SA, ABA, and ROS in P. cucumerina resistance vary between studies (Thomma et al, 1998;Ton and Mauch-Mani, 2004;Sánchez-Vallet et al, 2012;Gamir et al, 2014).…”

“…Because P. cucumerina can infect Arabidopsis leaves, the P. cucumerina-Arabidopsis interaction has emerged as a popular model system in which to study plant defense reactions to necrotrophic fungi (BerrocalLobo et al, 2002;Ton and Mauch-Mani, 2004;Carlucci et al, 2012;Ramos et al, 2013). Various studies have shown that Arabidopsis deploys a wide range of inducible defense strategies against P. cucumerina, including JA-, SA-, ABA-, and auxin-dependent defenses, glucosinolates (Tierens et al, 2001;Sánchez-Vallet et al, 2010;Gamir et al, 2014;Pastor et al, 2014), callose deposition (García-Andrade et al, 2011;Gamir et al, 2012Gamir et al, , 2014Sánchez-Vallet et al, 2012), and ROS (Tierens et al, 2002;Sánchez-Vallet et al, 2010;Barna et al, 2012;Gamir et al, 2012Gamir et al, , 2014Pastor et al, 2014). Recent metabolomics studies have revealed large-scale metabolic changes in P. cucumerina-infected Arabidopsis, presumably to mobilize chemical defenses (Sánchez-Vallet et al, 2010;Gamir et al, 2014;Pastor et al, 2014).…”

The Arabidopsis LYSIN MOTIF-CONTAINING RECEPTOR-LIKE KINASE3 Regulates the Cross Talk between Immunity and Abscisic Acid Responses

“…Also, Arabidopsis plants defective in ABA biosynthesis or signaling exhibit an increased resistance to B. cinerea (Adie et al, 2007). More recently, Arabidopsis mutants impaired in ABA biosynthesis or perception/transduction have been shown to have increased resistance to another necrotrophic fungus, Plectosphaerella cucumerina, as well as constitutive expression of defense responses (Sánchez-Vallet et al, 2012). However, the mechanisms linking a reduced ABA accumulation or perception/transduction to resistance to fungal infection are not fully elucidated.…”