Comparative genomics and functional studies of wheat BED-NLR loci

Nucleotide-binding, Leucine-rich-repeat (LRR) Receptors (NLRs) with non-canonical integrated domains (NLR-IDs) are widespread in plant genomes. Zinc-finger BED (named BED hereafter) are among the most frequently found IDs. Five BED-NLRs conferring resistance against bacterial and fungal pathogens have been characterized. However, it is unknown whether BED-NLRs function in a manner similar to other NLR-IDs. Here we used chromosome-level assemblies of wheat to explore the Yr7 and Yr5a genomic region and show that unlike known NLR-ID loci, there is no evidence for a NLR-partner in their vicinity. Using neighbor-network analyses, we observed that BED domains from BED-NLRs share more similarities with BED domains from single-BED proteins and from BED-DUF4413/659(-hAT) proteins. We identified a nuclear localization signal (NLS) in Yr7, Yr5 and the other characterized BED-NLRs; we thus propose that this is a feature of BED-NLRs that confer resistance to plant pathogens. We show that the NLS was functional in truncated versions of the Yr7 protein when expressed in N. benthamiana. We did not observe cell-death upon overexpression of Yr7 full-length, truncated and MHD variants in N. benthamiana. This suggests that either this system is not suitable to study BED-NLR signaling or BED-NLRs require additional components to trigger cell death. These results define novel future directions to further understand the role of BED domains in BED-NLR mediated resistance.