Email: tfahima@evo.haifa.ac.il

Plants employ numerous innate immune receptors to perceive various immunogenic signals associated with pathogen infection and activate defense responses. These receptors include cell-surface receptor-like kinases (RLKs) and intracellular nucleotide-binding leucine-rich repeats (NLRs). Yet, pathogens continuously develop counter-defenses in an arms race with their hosts, destabilizing food production and sustainability and resulting in global food insecurity. Thus, breeders seek durable broad-spectrum resistance (BSR) that can last many years.

We previously cloned the yellow rust BSR resistance gene, Yr15, derived from wild emmer wheat (Nature Communications 2018) that encodes a protein with a kinase-pseudokinase domain architecture, designated as Wheat Tandem Kinase 1 (WTK1).  The cloning of WTK1 led us to discover a novel protein family with a unique tandem kinase protein (TKP) architecture distributed across the plant kingdom. Phylogenetic analysis indicated that TKP family members are associated with RLKs and originated from either gene duplication or gene fusion events, implying a polyphyletic origin of the TKPs by convergent molecular evolution.

We hypothesize that TKPs serve as decoys that counter-defend the suppression of RLKs by pathogen effectors. Whole transcriptome analysis of wheat near-isogenic lines revealed that WTK1 activates defense-associated transcriptional reprogramming upon pathogen infection, leading to disease resistance.

The decoy model can explain how TKPs regulate the activation of local programmed cell death immune responses and provide support for TKP's polyphyletic origin and evolution. Currently, nine functional wheat TKPs were described by different groups, conferring resistance against rusts (WTK1, WTK2, WTK5, WTK6-vWA), powdery mildew (WTK3, WTK4, WTK7-TM, Pm57), and wheat blast (Rwt4) diseases. Yr15 (WTK1) confers resistance to >2000 pathogen isolates from around the globe, and we developed functional molecular markers for marker-assisted breeding.

Thus, TKPs have a great potential for resistance breeding. Further studies are underway to elucidate the mechanism of resistance conferred by this extraordinary protein family.