Mechanism driving intron-exon shuffling of PSY 3 genes in Grasses. (a) PSY 3 gene evolution among Grasses. The modern structure of the PSY 3 gene identified in rice, wheat, Brachypodium, maize and sorghum is shown at the bottom with coloured boxes representing conserved exons. The ancestral as well as pooideae and panicoideae PSY 3 is structured in five introns and lineage-specific intron losses and consequently exon fusions in wheat, Brachypodium and sorghum are illustrated according to the text description. (b) Representation of intron loss mechanism identified for the wheat PSY 3 with inverted and repeated motives that may have driven intron loss through replication slippage via the formation and a DNA loop. (c) Motifs identified at the deletion breakpoints and involved in intron loss due to illegitimate recombination at the splicing site are shown in red.