College of Life Sciences, Nanjing Normal University, Nanjing 210023, China.
Int J Mol Sci. 2017 Nov 2;18(11):2307. doi: 10.3390/ijms18112307.
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. 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 and . The comparison results showed a nearly identical organization in plastomes, indicating that the plastomic organization is highly conserved in genus. Furthermore, the impact of three evolutionary forces-selection, mutational biases, and GC-biased gene conversion (gBGC)-on the variation of GC content in 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 genus.
GC 含量的变化是基因组的一个关键特征，因为它与基因组组织的基本要素有关。然而，这种变化的原因仍然是一个悬而未决的问题。已经提出了不同种类的假说来解释基因组进化过程中 GC 含量的变化。然而，这些假说并没有在整个质体基因组序列中得到明确的研究。 是兰花物种中最大的属之一。该属的质体基因组组织和碱基组成的进化研究受到限制。在这项研究中，我们获得了 和 的高质量质体基因组序列。比较结果表明， 质体基因组的组织几乎相同，这表明质体基因组组织在 属中高度保守。此外，还评估了选择、突变偏倚和 GC 偏向基因转换 (gBGC) 这三种进化力量对 质体 GC 含量变化的影响。我们的结果表明：(1) 在单拷贝 (SC) 和反向重复 (IR) 区存在一致的 GC 含量进化趋势和突变偏倚；以及 (2) gBGC 影响了质体全基因组 GC 含量的进化。这些结果表明，突变偏倚和 gBGC 都影响了 属的质体基因组的 GC 含量。
