Genomic Instability and Shared Mechanisms for Gene Diversification in Two Distant Immune Gene Families: The Plant NBS-LRR Genes and the Echinoid 185/333 Genes

Innate immune systems in both animals and plants that lack somatic recombination and assembly mechanisms rely on a limited, preset number of genes encoding pathogen-recognition proteins that target universal pathogen-associated molecular patterns and/or monitor pathogen effector activity. To keep up with the ever-expanding diversity and virulence of pathogens, host mechanisms have evolved through selection to promote diversification of genomic regions that harbor immune genes. Here we review and compare the genomic structure and possible gene diversification mechanisms of two immune gene families: the nucleotide binding site leucine rich repeat (. NBS-LRR) genes in higher plants, and the 185/333 genes in sea urchins. These two gene families, which are present in organisms from two separate kingdoms, are very distinct in their abundance, structure, and function. Nevertheless, they share some fundamental genomic diversification strategies that may be the consequence of convergent evolutionary forces.