Plant and prokaryotic TIR domains generate distinct cyclic ADPR NADase products

Abstract

Toll/interleukin-1 receptor (TIR) domain proteins function in cell death and immunity. In plants and bacteria, TIR domains are enzymes that produce isomers of cyclic ADPR (cADPR) as putative immune signaling molecules. The identity and functional conservation of cADPR isomer signals is unclear. A previous report found that a plant TIR could cross-activate the prokaryotic Thoeris TIR-immune system, suggesting the conservation of plant and prokaryotic TIR-immune signals. Here, we generate auto-active Thoeris TIRs and test the converse hypothesis: do prokaryotic Thoeris TIRs also cross-activate plant TIR-immunity? Using in planta and in vitro assays, we find that Thoeris and plant TIRs generate overlapping sets of cADPR isomers, and further clarify how plant and Thoeris TIRs activate the Thoeris system via producing 3cADPR. This study demonstrates that the TIR-signaling requirements for plant and prokaryotic immune systems are distinct and that TIRs across kingdoms generate a diversity of small molecule products.