Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA.
New Phytol. 2010 Jan;185(1):27-41. doi: 10.1111/j.1469-8137.2009.03054.x. Epub 2009 Oct 23.
The extant land plants are unique among the monophyletic clade of photosynthetic eukaryotes, which consists of the green algae (chlorophytes), the charophycean algae (charophytes), numerous groups of unicellular algae (prasinophytes) and the embryophytes, by possessing, firstly, a sexual life cycle characterized by an alternation between a haploid, gametophytic and a diploid, sporophytic multicellular generation; secondly, the formation of egg cells within multicellular structures called archegonia; and, thirdly, the retention of the zygote and diploid sporophyte embryo within the archegonium. We review the developmental, paleobotanical and molecular evidence indicating that: the embryophytes descended from a charophyte-like ancestor; this common ancestor had a life cycle with only a haploid multicellular generation; and the most ancient (c. 410 Myr old) land plants (e.g. Cooksonia, Rhynia and Zosterophyllum) had a dimorphic life cycle (i.e. their haploid and diploid generations were morphologically different). On the basis of these findings, we suggest that the multicellular reproductive structures of extant charophytes and embryophytes are developmentally homologous, and that those of the embryophytes evolved by virtue of the co-option and re-deployment of ancient algal homeodomain gene networks.
现存的陆地植物在光合真核生物的单系分支中是独一无二的，该分支由绿藻（叶绿素）、石莼藻类（石莼类）、众多单细胞藻类（原绿藻）和胚胎植物组成，其特征首先是具有有性生命周期，其特征是在单倍体、配子体和二倍体、孢子体多细胞世代之间交替；其次，在称为颈卵器的多细胞结构中形成卵细胞；第三，受精卵和二倍体孢子体胚胎保留在颈卵器内。我们回顾了发育、古植物学和分子证据，表明：胚胎植物起源于石莼状祖先；这个共同的祖先具有只有一个单倍体多细胞世代的生命周期；最古老的（约 4.10 亿年前）陆地植物（如 Cooksonia、Rhynia 和 Zosterophyllum）具有二态生命周期（即它们的单倍体和二倍体世代在形态上不同）。基于这些发现，我们认为现存石莼类和胚胎植物的多细胞生殖结构在发育上是同源的，并且胚胎植物的那些结构是通过古老藻类同源域基因网络的选择和重新部署进化而来的。
