Variation in GC content is assumed to correlate with various processes, including mutation biases, recombination, and environmental parameters. To date, most genomic studies exploring the evolution of GC content have focused on nuclear genomes, but relatively few have concentrated on organelle genomes. We explored the mechanisms maintaining the GC content in angiosperm plastomes, with a particular focus on the hypothesis of phylogenetic dependence and the correlation with deletion mutations. We measured three genetic traits, namely, GC content, A/T tracts, and G/C tracts, in the coding region of plastid genomes for 1382 angiosperm species representing 350 families and 64 orders, and tested the phylogenetic signal. Then, we performed correlation analyses and revealed the variation in evolutionary rate of selected traits using RRphylo. The plastid GC content in the coding region varied from 28.10% to 43.20% across angiosperms, with a few non-photosynthetic species showing highly reduced values, highlighting the significance of functional constraints. We found strong phylogenetic signal in A/T tracts, but weak ones in GC content and G/C tracts, indicating adaptive potential. GC content was positively and negatively correlated with G/C and A/T tracts, respectively, suggesting a trade-off between these two deletion events. GC content evolved at various rates across the phylogeny, with significant increases in monocots and Lamiids, and a decrease in Fabids, implying the effects of some other factors. We hypothesize that variation in plastid GC content might be a mixed strategy of species to optimize fitness in fluctuating climates, partly through influencing the trade-off between AT → GC and GC → AT mutations.

假设 GC 含量的变化与各种过程相关，包括突变偏差、重组和环境参数。迄今为止，大多数探索 GC 内容进化的基因组研究都集中在核基因组上，但相对较少集中在细胞器基因组上。我们探讨了维持被子植物质体中 GC 含量的机制，特别关注系统发育依赖性假设和与缺失突变的相关性。我们测量了代表 350 个科和 64 个目的 1382 个被子植物的质体基因组编码区的 GC 含量、A/T 束和 G/C 束三个遗传性状，并测试了系统发育信号。然后，我们进行了相关性分析，并使用 RRphylo 揭示了所选性状进化速率的变化。被子植物编码区的质体 GC 含量从 28.10% 到 43.20% 不等，少数非光合物种显示出高度降低的值，突出了功能限制的重要性。我们在 A/T 束中发现了强的系统发育信号，但在 GC 含量和 G/C 束中发现了弱的系统发育信号，表明具有适应性潜力。GC 含量分别与 G/C 和 A/T 束呈正相关和负相关，表明这两个删除事件之间存在权衡。GC 含量在整个系统发育中以不同的速率进化，单子叶植物和 Lamiids 显着增加，Fabids 减少，这暗示了一些其他因素的影响。我们假设质体 GC 含量的变化可能是物种在波动气候中优化适应性的混合策略，