Evolution of switchgrass ( Panicum virgatum L.) based on sequences of the nuclear gene encoding plastid acetyl-CoA carboxylase

Switchgrass, Panicum virgatum, is a perennial grass native to the USA and Canada with an array of ploidy levels and ecotypes. In this study, genetic variation in the nuclear gene encoding plastid acetyl-CoA carboxylase from six switchgrass cultivars was investigated with the goal of defining relationships among these populations using DNA sequence comparisons. Four polymorphic sites were found in exons and 18 polymorphic sites plus four indels were found in introns within a 1828-nucleotide sequence alignment (696 nucleotides in exons and 1132 nucleotides in introns) of 27 genes. The homoeologous genomes of tetraploid and octaploid switchgrass are very closely related to each other, and among and between lowland and upland switchgrass ecotypes. Based on the molecular clock determined earlier for the Triticeae tribe, the genome divergence time and the time of the polyploidization events which established various contemporary switchgrass lineages was estimated to be less than 2 million years ago.