RECONSTRUCTING THE ANCESTRAL FEMALE GAMETOPHYTE OF ANGIOSPERMS: INSIGHTS FROM AMBORELLA AND OTHER ANCIENT LINEAGES OF FLOWERING PLANTS
RECONSTRUCTING THE ANCESTRAL FEMALE GAMETOPHYTE OF ANGIOSPERMS: INSIGHTS FROM AMBORELLA AND OTHER ANCIENT LINEAGES OF FLOWERING PLANTS
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DOI：
10.3732/ajb.0800311
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发表时间：
2009-01-01
影响因子：
3
通讯作者：
Ryerson, Kirsten C.
中科院分区：
文献类型：
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作者：
Friedman, William E.;Ryerson, Kirsten C.
世纪以来，有花植物的共同祖先被认为拥有七细胞八核的蓼型雌配子体。现在很明显，不是一个，但事实上，三个模式的雌配子体发育和成熟的结构特征的共同祖先的四个最古老的分支现存的被子植物：Amborella型，Nuphar/Eschandra型和蓼型。Amborella型雌配子体仅限于一个现存的物种，Amborella spicipoda，成熟时由8个细胞和9个核组成。Amborella型配子体的发育基本上与Polygonum型相同，除了在成熟之前在珠孔极处有额外的和异步的细胞分裂，产生第三助细胞和卵细胞。Nuphar/Escherichandra型雌配子体为四核四细胞型，成熟时含有典型的三细胞卵器和一个中央细胞，中央细胞具有一个单倍性极核。这种类型的配子体似乎是普遍存在于睡莲目（包括Hydatellaceae）和澳贝目（Austrobaileyales）的现存成员中。通过对特征分布和进化的重建，确认蓼型雌配子体是单子叶植物、真双子叶植物、木兰科植物、金鱼藻科植物和金粟兰科植物共同祖先的代表。有令人信服的生物学理由表明，四细胞，四核雌配子体（如在睡莲目和Austrobaileyales中发现的）是被子植物中的祖先，在Amborellales和古代被子植物分支（包括除Amborella，Nymphaeales和Austrobaileyales之外的所有被子植物）中分别过渡到Polygonum型雌配子体。在Amborellales中进化出七细胞八核的蓼型雌配子体后，我们推测卵器细胞数量发生了变态性的增加，并导致了Amborellaispoda中有三个助细胞的独特情况。
For more than a century, the common ancestor of flowering plants was thought to have had a seven-celled, eight-nucleate Polygonum-type female gametophyte. It is now evident that not one, but in fact three, patterns of female gametophyte development and mature structure characterize the common ancestors of the four most ancient clades of extant angiosperms: Amborella-type, Nuphar/Schisandra-type and Polygonum-type. The Amborella-type female gametophyte is restricted to a single extant species, Amborella trichopoda, and at maturity consists of eight cells and nine nuclei. Development of the Amborella-type gametophyte is essentially identical to the Polygonum-type except that there is an additional and asynchronous cell division at the micropylar pole prior to maturation that produces a third synergid and the egg cell. The Nuphar/Schisandra-type female gametophyte is four-nucleate and four-celled and at maturity contains a typical three-celled egg apparatus and a central cell with a single haploid polar nucleus. This type of gametophyte appears to be universal among extant members of the Nymphaeales (including Hydatellaceae) and Austrobaileyales. Based on explicit reconstruction of character distribution and evolution, the Polygonum-type female gametophyte is certain to be representative of the common ancestors of monocots, eudicots, magnoliids, Ceratophyllaceae, and Chloranthaceae. There are compelling biological reasons to suggest that the four-celled, four-nucleate female gametophyte (as found in Nymphaeales and Austrobaileyales) is ancestral among angiosperms, with transition,, to Polygonum-type female gametophytes separately in the Amborellales and in the ancient angiosperm clade that includes all angiosperms except Amborella, Nymphaeales, and Austrobaileyales. Subsequent to the evolution of a seven-celled, eight-nucleate Polygonum-type female gametophyte in the Amborellales, we hypothesize that a peramorphic increase in egg apparatus cell number took place and led to the unique situation in which there are three synergids in Amborella trichopoda.