Diversification of Disease Resistance Receptors by Integrated Domain Fusions in Wheat and its Progenitors

Abstract

Pathogenic effectors inhibit plant resistance responses by interfering with intracellular signaling mechanisms. Plant Nucleotide-binding, Leucine-rich repeat Receptors (NLRs) have evolved highly variable effector-recognition sites to detect these effectors. While many NLRs utilize variable Leucine-Rich Repeats (LRRs) to bind to effectors, some have gained Integrated Domains (IDs) necessary for receptor activation or downstream signaling. While a few studies have identified IDs within NLRs, the homology and regulation of these genes have yet to be elucidated. We identified a diverse set of wheat NLR-ID fusion proteins as candidates for NLR functional diversification through ID effector recognition or signal transduction. NLR-ID diversity corresponds directly with the various signaling components essential to defense responses, expanding the potential functions for immune receptors and removing the need for intermediate signaling factors that are often targeted by effectors. ID homologs (>80% similarity) in other grasses indicate that these domains originated as functional, non-NLR-encoding genes and were incorporated into NLR-encoding genes through duplication. Multiple NLR-ID genes encode experimentally verified alternative transcripts that include or exclude IDs. This indicates that plants employ alternative splicing to regulate IDs, possibly using them as baits, decoys, and functional signaling components. Future studies should aim to elucidate differential expression of NLR-ID alternative transcripts.