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Archive for the ‘Plant Evolution’ Category

taxis.jpgMoving Genes Around

A recent report that a species of aphid can make carotene thanks to a gene it apparently acquired from a fungus got me to thinking about whether genes can flow between different plant species.

When an organism incorporates genetic material from another organism without being the offspring of that organism, this is called horizontal gene transfer (HGT), a.k.a., “lateral gene transfer”. (Vertical gene transfer occurs between parent and offspring.)

HGT is common in bacteria – it’s often how bacteria acquire genes for drug resistances, for instance.

Although much less common, there are cases of HGT between microbes and plants. (An excellent review can be found here.) Interest the subject of HGT in plants has been stimulated by the proliferation of GMO’s, especially transgenic crop plants, see here, for example.

The natural transfer of genes between fungi, bacteria and plants has been established, but to what degree will likely have to await a more complete array of genetically-sequenced plants.

Parasites as a Bridge for Gene Flow Between Diverse Plant Species

Striga_hermonthica.jpgParasitic plants form vascular connections with their host plants via haustoria to allow transfer of nutrients, water, and even mRNAs ( see Ref 1 below). Thus, it has been suspected that HGT of nuclear genes may occur in parasitic plants.

In a recent report, scientists have found evidence for nuclear gene transfer in the parasitic plant Striga. “Striga hermonthica (Del.) Benth. is a devastating parasitic plant that infests members of the grass family (Poaceae), including major crops such as sorghum (Sorghum bicolor) and rice (Oryza sativa).” (from Ref 2 below)

Briefly, these investigators searched for grass-specific genes within the genome of Striga. They did indeed find at least one grass specific gene. Thus, “…our comparative genomics analysis of a eudicot parasite and its monocot hosts presents a clear case for nuclear HGT.” (from Ref 2)

Bottom line: Research over the past decade has provided evidence that gene movement between distantly related plant species occurs, and that plant parasites are likely a vehicle for such movement.

Recent news regarding gene movement in fungi.

References

1. Westwood, J. H, J. I. Yoder, M. P. Timko, and C. W. dePamphilis (2010) “The evolution of parasitism in plants.” Trends in Plant Science Vol. 15, pp. 227-235. (Abstract)

2. Yoshida, S., S. Maruyama, H. Nozaki, and K. Shirasu (2010) “Horizontal gene transfer by the parasitic plant Striga hermonthica.” Science Vol. 328, p. 1128. (Abstract)

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412032028_ebd346be77_m.jpgA Long, Long Time Ago on Planet Not So Far Away

What were the first plants to colonize the land on Earth? And when did this occur in the history of the biosphere?

Why did a burgeoning of flowering plant species come to dominate their gymnosperm and fern predecessors so quickly?

The Mossy (Algal and Fungal) Earth

Most biology textbooks state that plant life emerged on land about 450 million years ago (e.g, see p.4, The Biology of Plants by Raven, Evert & Eichhorn).

A new study suggests that plants colonized land much earlier than this.

As summarized here, the authors L. Paul Knauth and Martin J. Kennedy think that their geochemical data suggests that photosynthetic life forms (largely mats composed of mosses and algae, accompanied by fungi) carpeted the land over 800 million years ago.

Their evidence, albeit indirect, may help to explain the increase in atmospheric oxygen levels that allowed for the evolution of relatively large respirating animals about 600 MYA.

This green “welcome mat” may have set the stage for animal colonization of the land.

The “Abominable Mystery” of the Conquering Flowers

3345633461_b7110a4113.jpgIt’s been over 100 years since Charles Darwin described it as an “abominable mystery”.

What was perplexing Darwin was the fossil evidence that flowering plants (angiosperms) rapidly diversified and spread across the planet. (This was at odds with his belief that evolution was a gradual process.)

A new theory has been proposed in an attempt to solve this “mystery”.

As brilliantly summarized here, flowering plants may have taken advantage of changes in soil fertility, which were due largely to the higher growth and turnover rates of angiosperms compared to gymnosperms. Thus, a sort of positive feedback loop was created that allowed for the rapid proliferation of flowering plant species.

The originators of this theory, Frank Berendse and Marten Scheffer, published this ecological explanation of Darwin’s “abominable mystery” in Ecology Letters.

Bottom Line: Looks like studying the soil can provide answers to botanical questions.

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