Supernetwork Identifies Multiple Events of Plastid trnF(GAA) Pseudogene Evolution in the Brassicaceae

The occurrence of nonfunctional trnF pseudogenes has been rarely described in flowering plants. However, we describe the first large-scale supernetwork for the Brassiccaeae built from gene trees for 5 loci (adh, chs, matK, trnL-F, and ITS) and report multiple independent origins for trnF pseudogenes in crucifers. The duplicated regions of the original trnF gene are comprised of its anticodon domain and several other highly structured motifs not related to the original gene. Length variation of the trnL-F intergenic spacer region in different taxa ranges from 219 to 900 bp as a result of differences in pseudocopy number (1-14). It is speculated that functional constraints favor 2-3 or 5-6 copies, as found in Arabidopsis and Boechera. The phylogenetic distribution of microstructural changes for the trnL-F region supports ancient patterns of divergence in crucifer evolution for some but not all gene loci.