A new plant immunity regulator that controls the production of reactive oxygen species during disease resistance responses

The group of "Plant Innate immunity and resistance to necrotrophic fungi", led by Dr. Antonio Molina at the CBGP (UPM-INIA), described previously that heterotrimeric G protein is a master regulator of plant immunity since Arabidopsis thaliana mutant impaired in the Gb subunit (agb1-2) is highly susceptible to different pathogens and shows defective activation of immune responses (Llorente et al., 2005; Delgado-Cerezo et al., 2012). To characterise the function of Gb in immunity the Molina´s lab performed a mutant screening to identify suppressors of agb1-2 susceptibility (sgb) to pathogens. This screening led to the identification of sgb10 mutant that was found to be impaired in MKP1 gene that encodes the Mitogen Activated Protein Kinase Phosphatase 1. Remarkably, MKP1 was found to negatively balance the production of reactive oxygen species (ROS) that is triggered upon pathogen attack or plant perception of Microbe-Associated Molecular Patterns (MAMPs). ROS production is essential for an effective immune response and is mediated by the NADPH oxidase RBOHD. Remarkably, ROS production is enhanced in mkp1 mutant plants during the activation of the immune responses. The CBGP researchers demonstrate that MPK1 regulates RBOHD activity both at the transcriptional and activity levels, since RBOHD is upregulated in mkp1 upon pathogen infection or MAMP treatment, and RBOHD enzymatic activity is negatively regulated by MKP1. MPK1 also regulates other immune responses like the synthesis of immunity-associated metabolites (e.g. antimicrobial compounds and defensive hormones). Together these data indicate that MKP1 functions downstream of the heterotrimeric G protein during plant immunity balancing the amplitude of the immune responses. This work opens the possibility to design novel disease resistance strategies to increase crop protection against a broad range of pathogens.

Figure 1. mpk1 mutants show enhanced RBOHD expression. In vivo bioluminescence in 3-week-old Arabidopsis thaliana plants expressing the Luciferase (LUC) protein under the control of the RBOHD gene promoter (pD::LUC). Pictures were taken 24 hours after infection of the plants with the necrotrophic fungus Plectosphaerella cucumerina (PcBMM) or treatment with water (Mock). The bioluminescence signal is derived from the activity of LUC protein, which is expressed upon transcriptional regulation of RBOHD promoter. LUC expression and bioluminescence are enhanced in plants harbouring the mkp1 mutation and are reduced in plant overexpressing MKP1 (35S::MKP1).

Original Paper:

Escudero, V., Torres, M.A., Delgado, M., Sopeña-Torres, S., Swami, S., Morales, J., Muñoz-Barrios, A., Mélida, H., jones, A.M., Jordá, L., Molina, A., 2018. "Mitogen-activated protein kinase phosphatase 1 (MKP1) negatively regulates the production of Reactive Oxygen Species during Arabidopsis immune responses". Molecular Plant-Microbe Interactions. DOI: 10.1094/MPMI-08-18-0217-FI