Evolution of Resistance Genes in Magnoliids: Dramatic Expansions of and Multiple Losses of .

Magnoliids are the third-largest group of angiosperms and occupy a critical position in angiosperm evolution. In the past years, due to the lack of sequenced genomes, the disease resistance gene ( gene) profile of magnoliids remains poorly understood. By the genome-wide identification of 1,832 genes from seven magnoliid genomes, we built a framework for the evolution of magnoliid genes. genes were completely absent from five magnoliids, presumably due to immune pathway deficiencies. A total of 74 ancestral genes (70 , 3 , and 1 ) were recovered in a common ancestor of magnoliids, from which all current gene repertoires were derived. Tandem duplication served as the major drive for genes expansion in seven magnoliid genomes, as most surveyed angiosperms. Due to recent rapid expansions, most magnoliids exhibited "a first expansion followed by a slight contraction and a further stronger expansion" evolutionary pattern, while both and showed a two-times-repeated pattern of "expansion followed by contraction." The transcriptome analysis of seven different tissues of revealed a low expression of most genes, with some genes displaying a relatively higher expression in roots and fruits. Overall, our study sheds light on the evolution of genes in magnoliids, compensates for insufficiency in major angiosperm lineages, and provides an important reference for a better understanding of angiosperm genes.