Wolfe K H, Gouy M, Yang Y W, Sharp P M, Li W H
Center for Demographic and Population Genetics, University of Texas, Houston 77225.
Proc Natl Acad Sci U S A. 1989 Aug;86(16):6201-5. doi: 10.1073/pnas.86.16.6201.
The divergence between monocots and dicots represents a major event in higher plant evolution, yet the date of its occurrence remains unknown because of the scarcity of relevant fossils. We have estimated this date by reconstructing phylogenetic trees from chloroplast DNA sequences, using two independent approaches: the rate of synonymous nucleotide substitution was calibrated from the divergence of maize, wheat, and rice, whereas the rate of nonsynonymous substitution was calibrated from the divergence of angiosperms and bryophytes. Both methods lead to an estimate of the monocot-dicot divergence at 200 million years (Myr) ago (with an uncertainty of about 40 Myr). This estimate is also supported by analyses of the nuclear genes encoding large and small subunit ribosomal RNAs. These results imply that the angiosperm lineage emerged in Jurassic-Triassic time, which considerably predates its appearance in the fossil record (approximately 120 Myr ago). We estimate the divergence between cycads and angiosperms to be approximately 340 Myr, which can be taken as an upper bound for the age of angiosperms.
单子叶植物和双子叶植物之间的分化是高等植物进化中的一个重大事件，但由于相关化石稀少，其发生时间仍然未知。我们通过两种独立的方法，从叶绿体DNA序列重建系统发育树来估计这个时间：同义核苷酸替换率是根据玉米、小麦和水稻的分化进行校准的，而非同义替换率是根据被子植物和苔藓植物的分化进行校准的。两种方法都得出单子叶植物和双子叶植物在2亿年前发生分化的估计（不确定性约为4000万年）。对编码核糖体RNA大亚基和小亚基的核基因的分析也支持了这一估计。这些结果表明，被子植物谱系出现在侏罗纪-三叠纪时期，这比其在化石记录中的出现时间（约1.2亿年前）要早得多。我们估计苏铁类植物和被子植物之间的分化时间约为3.4亿年，这可以作为被子植物年龄的上限。
