Why red algae never colonized dry land

Mar 21, 2013
In the foreground, the red alga, Chondrus crispus. Credit: Jonas Collén

The first red alga genome has just been sequenced by an international team coordinated by CNRS and UPMC at the Station Biologique de Roscoff (Brittany), notably involving researchers from CEA-Genoscope, the universities of Lille 1 and Rennes 1 and the Muséum National d'Histoire Naturelle. The genome of Chondrus crispus, also known by the Breton name 'pioka', turns out to be small and compact for a multicellular organism. It has fewer genes than several other species of unicellular algae, which raises a number of questions about the evolution of red algae. This low number of genes could explain why these organisms never colonized dry land, unlike their green counterparts-from which all terrestrial plants are descended. These findings open up new perspectives on the natural history of algae and of terrestrial plants. They are published online in the journal PNAS on March 11, 2013.

Chondrus crispus is a multicellular red alga of about 20 cm in length. It is very common on the rocky coasts of the North Atlantic where it plays an essential role as a primary producer in these ecosystems. Certain are now used in the agri-food industry for the thickening properties of the carrageenans from their cell walls. These sulfated polysaccharides correspond to the food additive E-407, which goes into many desserts and other dishes. Beyond industrial applications, this first sequencing of a red alga genome sheds new light on as a whole.

Why red algae never colonized dry land
A Chondrus crispus red alga. Credit: Jonas Collén

The Chondrus genome had some surprises in store for the researchers. With only 9,606 genes and 105 million , it is indeed very small for a multicellular organism. By way of comparison, the unicellular has 14,516 genes, while the multicellular terrestrial plant Arabadopsis thaliana has 27,416. The Chondrus genome is also very compact, with each function generally corresponding to a single gene. Gene families are small, and genes closely spaced.

To explain these surprising characteristics, the researchers proposed the hypothesis that, more than a billion years ago, red algae experienced a massive loss of genetic material as a result of extreme environmental conditions. This dramatic event in their evolutionary history would have had many consequences. One result could be the loss of flagellar genes, still present in most other organisms and responsible for the motility of certain cells (such as the gametes during sexual reproduction in most organisms, including humans).

Had this massive gene loss never occurred, red algae might have extensively colonized the terrestrial environment, in the same way as green algae, which are the ancestors of all land plants. Yet this event-a real evolutionary bottleneck-has denied red algae the plasticity and genetic potential necessary to adapt to life on land.

The sequence of the Chondrus genome thus opens the archives of more than 1,500 million years of evolutionary history of terrestrial and marine plants. It provides a new basis for the study of red algae biology and is the first step in a program aiming to improve our understanding of the origin of life on Earth, the adaptation of red algae to their environment and the biosynthesis pathways of biomolecules of interest, such as carrageenans. The scientists of the group are also hoping to discover new enzymes of interest for marine biotechnology.

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More information: Collen, J. et al. Genome structure and metabolic features in the red seaweed Chondrus crispus shed light on evolution of the Archaeplastida, PNAS. Available online March 11, 2013.

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1 / 5 (6) Mar 21, 2013
I'm also thinking that the green algae's ability to photosynthesize gave it the advantage over both red and brown algae in terms of survival, allowing it to become more adaptable, and thus, colonize the land, giving rise to the entire plant kingdom. The low number of genes is interesting, but perhaps that isn't the only reason.
3.2 / 5 (11) Mar 21, 2013
Apologies. I just did some further research on the subject. Seems I was plain wrong with that comment. Red and brown algae do, in fact, photosynthesize. And do so, with a much higher efficiency. Please disregard the above comment - I was going to remove it, but the edit button disappeared.
5 / 5 (5) Mar 21, 2013
Sinister, your honesty makes you a role model for the internet.

Anyway, if red and brown algae have effective photosynthesis, we may insert some of their genes into ordinary "green" plants to cover the whole solar spectrum more effciently using GM.
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Astrobiologists may speculate what a world would look like where a red algae analogue evolved without undergoing diversity loss.
3 / 5 (4) Mar 21, 2013
This low number of genes could explain why these organisms never colonized dry land, unlike their green counterparts-from which all terrestrial plants are descended
It could be consequence of it as well. The life in water is simpler, evolution slower, number of genes is therefore lower. Whereas the brown color is well adopted to utilization of underwater bluish light, it would suffer with excess of heat and energy at the dry land. The first problem, which the green plants had to solve was their cooling - they're very "pale" in the infrared spectrum.
2.6 / 5 (5) Mar 22, 2013
Blue light filters through water much further and efficiently than the red part of the spectrum of light (which is absorbed more with given distance traveled in water) even in relatively shallow water but esp in deep water which is why the algae that has evolved there tends to be more specialized at photosynthesizing using the blue light but often not the red light.
The red photosynthetic pigment in red algae is generally more efficient at using this blue light than the red light which explains why many sea algae are red. On land, the red light has to pass through little or no water before it reaches the plants so it is not blocked much and green photosynthetic pigment in green plants can use this red light while the red photosynthetic pigment in red algae simply wastes it so that is why most plants on land are green because being green makes more efficient photosynthesis using the more reddish light you get on on land.

-Thus the articles explanation is nonsense!
5 / 5 (2) Mar 22, 2013
I'm more concerned what such bottlenecks from changed environments tells us about the potential of diversifying life on ever changing terrestrials. Plate tectonics is not ideal, but having smaller moons so little help against chaotic orbital tilts is not either.

Though the gaps between our own supercontinent cycle changes are about the same or even smaller than the chaotic long cycles of 500 million years of stability, so maybe I get overly concerned.
3 / 5 (2) Mar 23, 2013
Humy is actually right there so i gave him 5 stars to balance the one star given by someone with less knowledge in photosynthesis...

I have a feeling that this article doesn't adequately explain what the research was about since there is no good reason why efficiently photosynthesizing land plants would be red under any circumstance.
1 / 5 (5) Mar 24, 2013
Sinister, your honesty makes you a role model for the internet.

Thanks Birger. I've always been pretty honest. Although, I've never really considered myself a role model for anything. I am flattered by that compliment.

Astrobiologists may speculate what a world would look like where a red algae analogue evolved without undergoing diversity loss.

This is certainly an interesting thought. I wonder if they would've evolved in much the same way as plants did from green algae.

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