The evolution and function of protein tandem repeats in plants

Summary Sequence tandem repeats ( TR s) are abundant in proteomes across all domains of life. For plants, little is known about their distribution or contribution to protein function. We exhaustively annotated TR s and studied the evolution of TR unit variations for all Ensembl plants. Using phylogenetic patterns of TR units, we detected conserved TR s with unit number and order preserved during evolution, and those TR s that have diverged via recent TR unit gains/losses. We correlated the mode of evolution of TR s to protein function. TR number was strongly correlated with proteome size, with about one‐half of all TR s recognized as common protein domains. The majority of TR s have been highly conserved over long evolutionary distances, some since the separation of red algae and green plants c . 1.6 billion yr ago. Conversely, recurrent recent TR unit mutations were rare. Our results suggest that the first TR s by far predate the first plants, and that TR appearance is an ongoing process with similar rates across the plant kingdom. Interestingly, the few detected highly mutable TR s might provide a source of variation for rapid adaptation. In particular, such TR s are enriched in leucine‐rich repeats ( LRR s) commonly found in R genes, where TR unit gain/loss may facilitate resistance to emerging pathogens.