Natural variation in temperature-resilient immunity in Arabidopsis

Elevated temperature has been shown to compromise salicylic acid (SA)-mediated immunity in plants. The Arabidopsis thaliana accession C24 retains constitutively elevated SA and resistance to the hemibiotrophic pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) at elevated temperature. C24 exhibits reduced biomass compared to that of a commonly studied accession, Col-0, in which SA-mediated immunity is compromised at elevated temperature. Neither the genetic basis of temperature-resilient immunity (TRI) nor the apparent growth-defense tradeoff in C24 is known. Here, we show that a Col-0 x C24 recombinant inbred line (RIL) population resolves TRI to a chromosome 5 locus accounting for most of the mapped genetic variance. This locus (named TRI hereinafter) coincides with a hotspot of structural rearrangement between the two accessions and includes a calcium-sensor gene (CBL9) and several NLR-type paralogs found only in C24. Consistent with a calcium-dependent signaling component, C24 mounts an elevated cytosolic Ca{superscript 2} response to Pst DC3000. Surprisingly, across the RIL population, disease resistance and biomass are only weakly correlated, with some lines exhibiting both large biomass and high pathogen resistance. These results show that temperature-resilient disease resistance is not only genetically tractable in C24 but also can be uncoupled from biomass cost. The TRI locus in C24 therefore encodes a natural mechanism(s) of temperature-resilient immunity with the growth-defense tradeoff resolved.