Transition metal-triggered immunity via an Arabidopsis NLR pair
Plants growing in soil are challenged by multiple biotic (e.g. pathogens) and abiotic (e.g. heavy metals) stressors. Stress resistance is a key determinant for plants to thrive in the environment. Resistance to pathogens requires innate immunity , whereas tolerance to metal ions is accomplished by mechanisms such as complexation and compartmentation. Some transition metals can enhance plant's defense against pathogens4,5, but the mechanism remains unclear. Here, we show that an Arabidopsis head-to-head gene pair of intracellular nucleotide-binding leucine-rich repeat (NLR) receptors antagonistically control transition metal-triggered immunity. One NLR, STM2 directly perceives transition metal ions, such as Cd2+, Cu2+ and Zn2+, as a ligand to activate its NAD+ hydrolytic activity and immune responses, triggering enhanced resistance to the soil-borne bacterial wilt pathogen Ralstonia solanacearum. The other NLR, STM1 suppresses STM2 to protect plants from transition metal-triggered immunity and growth inhibition in the presence of excess metals. STM1 also dampens resistance to the pathogen. Our study defines an NLR activated by transition metals and reveals a trade-off between resistance to pathogens and tolerance to transition metals that are pervasive in soil. Overall design: To investigate the functional roles of STM1 and STM2 genes under Cd stress, we performed transcriptome analyses using plants with Col-0, stm1-1, stm2-2, stm2 stm1. Seedlings grown for 12 days were transferred to plates  with or without Cd(70 µM) for 16 h. Roots and Shoots were sampled separately, and later RNA-seq data from the above tissues were used for comparative analysis of gene expression profiles.