Pangenomic context reveals the extent of intraspecific plant NLR evolution

Abstract

Nucleotide-binding leucine-rich repeat (NLR) proteins are a major component of the plant immune system, which directly or indirectly detect molecular signals of pathogen invasion. Despite their critical role, the processes by which NLR genes diversify remain poorly characterised due to the extraordinary sequence, structural, and regulatory variability of NLRs, even among closely related individuals. To understand the evolution of NLR diversity in Arabidopsis thaliana, we leverage graph-based methods to define pangenomic NLR neighbourhoods in 17 genetically diverse genomes. We integrate full-length transcript and transposable element information to exhaustively annotate all intact and degraded NLRs, enabling exploration of the processes that underpin the birth, death and maintenance of NLR diversity within a species. Our main finding is that many uncorrelated mutational processes create NLR diversity, and that there is no single metric that captures on its own the true extent of NLR structural and sequence variation. This immense diversity in plant immune system diversification allows populations to survive the constant onslaught of pathogens, not unlike vertebrate adaptive immunity, where variation is also generated by a variety of complementary mechanisms, albeit at the level of individuals.