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Ancestors of land plants revealed

Date:
May 2, 2011
Source:
BioMed Central
Summary:
It was previously thought that land plants evolved from stonewort-like algae. However, new research shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra.

It was previously thought that land plants evolved from stonewort-like algae. However, new research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the closest relatives to land plants are actually conjugating green algae such as Spirogyra.

Ancestors of green plants began to colonise the land about 500 million years ago and it is generally accepted that they evolved from streptophyte algae (a group of green, fresh water algae). But this group of algae is very diverse and currently ranges from simple, one cell, flagellates to more complex, branching, algae such as stoneworts (Chara).

It was thought that Charales were the closest relatives to land plants because they share (amongst other characteristics) a similar method of fertilisation, oogamy, with a large egg and small swimming sperm. For flowering plants this sperm is contained within pollen grains. In contrast, another type of streptophytes, the Zygnematales, use conjugation, a method of reproduction where the gametes are of equal size, isogamy, and one or both crawl, amoeba-like, into a fertilization tube where they meet and fuse.

Some phylogenetic analysis had been done previously, on a smaller number of genes, which seemed to support the Charales theory. However, a multinational team, involving researchers in Germany and Canada, analysed genetic divergence in 129 genes from 40 different green plant taxa. This data showed that, despite the differences in reproductive strategy, the closest living relatives to land plants are in fact the Zygnematales.

Dr Becker explained, "It seems that Zygnematales have lost oogamy and their ability to produce sperm and egg cells, and instead, possibly due to selection pressure in the absence of free water, use conjugation for reproduction. Investigation of such a large number of genes has shown that, despite their apparent simplicity, Zygnematales have genetic traces of other complex traits also associated with green land plants. Consequently Zygnematales true place as the closest living relative to land plants has been revealed."


Story Source:

The above story is based on materials provided by BioMed Central. Note: Materials may be edited for content and length.


Journal Reference:

  1. Sabina Wodniok, Henner Brinkmann, Gernot Glφckner, Andrew J Heidel, Hervι Philippe, Michael Melkonian and Burkhard Becker. Origin of land plants: Do conjugating green algae hold the key? BMC Evolutionary Biology, (in press) [link]

Cite This Page:

BioMed Central. "Ancestors of land plants revealed." ScienceDaily. ScienceDaily, 2 May 2011. <www.sciencedaily.com/releases/2011/04/110417214202.htm>.
BioMed Central. (2011, May 2). Ancestors of land plants revealed. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2011/04/110417214202.htm
BioMed Central. "Ancestors of land plants revealed." ScienceDaily. www.sciencedaily.com/releases/2011/04/110417214202.htm (accessed July 28, 2014).

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