Streptophyte algae and the origin of embryophytes
Streptophyte algae and the origin of embryophytes
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DOI：
10.1093/aob/mcp044
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发表时间：
2009-05-01
期刊：
影响因子：
4.2
通讯作者：
Marin, Birger
中科院分区：
文献类型：
--
作者：
Becker, Burkhard;Marin, Birger
陆生植物（有胚植物）由链型植物绿藻进化而来，链型植物绿藻是一小类淡水藻类，包括从有鳞的单细胞鞭毛藻（中斑藻）到具有分支、细胞分化和顶端生长的复杂丝状叶状体（轮藻目）。链型植物藻类和有胚植物构成了链型植物门，而其余的绿藻则被归类为绿藻门。轮藻目（轮藻）通常被认为是陆生植物的姊妹类群，这表明链型植物绿藻在细胞复杂性方面逐渐进化。许多细胞特征（例如成膜体、胞间连丝、六聚体纤维素合酶、鞭毛细胞的结构、具有合子保留的卵式有性生殖）和生理特征（例如光呼吸类型、光敏色素系统）都起源于链型植物藻类。系统发育研究表明，中斑藻（鞭毛藻）和绿胞藻（八叠球菌状）在链型植物中最早分化出来，是包括有胚植物在内的所有其他链型植物的姊妹类群。轮藻目、鞘毛藻目或双星藻目是否是有胚植物的姊妹类群这一问题仍然（或者再次）受到激烈争论。包括蛋白质家族和多聚腺苷酸化信号在内的研究链型植物基因组进化的项目已经启动。与形态和生理特征一致，许多被认为是有胚植物特有的分子特征已被证明早于绿藻门/链型植物门的分化，或者起源于链型植物藻类。分子系统发育和化石记录能够详细重建导致真正陆生植物起源的早期进化事件，并塑造了链型植物绿藻及其有胚植物后代当前的多样性和生态学。链型植物门/绿藻门的分化与对淡水/海洋生境显著保守的偏好相关，链型植物藻类早期对淡水的适应对最早的陆生植物来说是一个主要优势，甚至在胚胎和孢子体世代起源之前就是如此。为了更好地理解链型植物对陆地生境的定殖，需要几个关键链型植物藻类类群的完整基因组。
Land plants (embryophytes) evolved from streptophyte green algae, a small group of freshwater algae ranging from scaly, unicellular flagellates (Mesostigma) to complex, filamentous thalli with branching, cell differentiation and apical growth (Charales). Streptophyte algae and embryophytes form the division Streptophyta, whereas the remaining green algae are classified as Chlorophyta. The Charales (stoneworts) are often considered to be sister to land plants, suggesting progressive evolution towards cellular complexity within streptophyte green algae. Many cellular (e.g. phragmoplast, plasmodesmata, hexameric cellulose synthase, structure of flagellated cells, oogamous sexual reproduction with zygote retention) and physiological characters (e.g. type of photorespiration, phytochrome system) originated within streptophyte algae.Phylogenetic studies have demonstrated that Mesostigma (flagellate) and Chlorokybus (sarcinoid) form the earliest divergence within streptophytes, as sister to all other Streptophyta including embryophytes. The question whether Charales, Coleochaetales or Zygnematales are the sister to embryophytes is still (or, again) hotly debated. Projects to study genome evolution within streptophytes including protein families and polyadenylation signals have been initiated. In agreement with morphological and physiological features, many molecular traits believed to be specific for embryophytes have been shown to predate the Chlorophyta/Streptophyta split, or to have originated within streptophyte algae. Molecular phylogenies and the fossil record allow a detailed reconstruction of the early evolutionary events that led to the origin of true land plants, and shaped the current diversity and ecology of streptophyte green algae and their embryophyte descendants.The Streptophyta/Chlorophyta divergence correlates with a remarkably conservative preference for freshwater/marine habitats, and the early freshwater adaptation of streptophyte algae was a major advantage for the earliest land plants, even before the origin of the embryo and the sporophyte generation. The complete genomes of a few key streptophyte algae taxa will be required for a better understanding of the colonization of terrestrial habitats by streptophytes.