Mutational Biases and GC-Biased Gene Conversion Affect GC Content in the Plastomes of Dendrobium Genus

Abstract

The variation of GC content is a key genome feature because it is associated with fundamental elements of genome organization. However, the reason for this variation is still an open question. Different kinds of hypotheses have been proposed to explain the variation of GC content during genome evolution. However, these hypotheses have not been explicitly investigated in whole plastome sequences. <i>Dendrobium</i> is one of the largest genera in the orchid species. Evolutionary studies of the plastomic organization and base composition are limited in this genus. In this study, we obtained the high-quality plastome sequences of <i>D. loddigesii</i> and <i>D. devonianum</i>. The comparison results showed a nearly identical organization in <i>Dendrobium</i> plastomes, indicating that the plastomic organization is highly conserved in <i>Dendrobium</i> genus. Furthermore, the impact of three evolutionary forces-selection, mutational biases, and GC-biased gene conversion (gBGC)-on the variation of GC content in <i>Dendrobium</i> plastomes was evaluated. Our results revealed: (1) consistent GC content evolution trends and mutational biases in single-copy (SC) and inverted repeats (IRs) regions; and (2) that gBGC has influenced the plastome-wide GC content evolution. These results suggest that both mutational biases and gBGC affect GC content in the plastomes of <i>Dendrobium</i> genus.