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some estimates are that 40-50% of angiosperms are polyploid. But WHY do plants tolerate genome duplication so well?
1. Energy abundance: Plants are, in general, not energy limited (as least not as much as animals). Often throughout evolution there is strong selective pressure on most animals to use energy as efficiently as possible. However, plants are often faced with problems of how to divert excess sunlight away to protect their proteins. Since this energy limitation is not as strong in plants they can afford to spend a bit more on things that might seem frivolous or too expensive to an animal, such as an enormous genome or multiple copies of the same genome.
2. An elaborate RNAi system. Plants have an elaborate RNAi system that includes both transcriptional and post-transcriptional gene silencing. Duplicate copies of some genes could be harmful directly or indirectly in the cost of producing proteins from them. It would be important for a plant (or animal) suddenly finding itself in possession of an extra two copies of all genes to be able to rapidly shut down production of proteins that could either be potentially harmful or costly to produce. Plants are well prepared to deal with this, they have several RNA dependent RNA polymerases, four Dicer proteins, several Argonaut proteins, all designed to keep proteins that aren't needed from being produced. Perhaps the plant-specific RNAPolIV is one reason plants can handle polyploidy better.
Thanks Colleen for some interesting speculation, which even if the speculation may be the wrong reasons, nonetheless does seem to raise even more interesting questions about the premisses for that speculation.
So, what is the situation with non-flowering plants?
Firstly, this seems at face value to imply that blanks are deliberately inefficient at energy conversion, and this could have an impact in their long term use for biofuels (either their conversion efficiency could be manipulated, or we might yet develop artificial solar energy conversion mechanisms that might exceed the conversion efficiency of plants).
Secondly, with regard to the specific speculation you are making, does that imply that fast growing plants are less polyploid than slower growing plants?
This sort of gene silencing sounds like it might be a useful viral protection scheme.
One other aspect I think may be the case (maybe you might comment) is that the species boundaries between plants is less sharply defined than in animals, hence it is easier to cross breed between plant species than animal species. This would imply that plants are better able to tolerate alien genes (consistent with your arguments above) than animals are, but still take something useful from the alien chromosomes while suppressing anything toxic within them. This too, I believe is one of the ways in which higher order polyploidism is introduced into plants species.
1. Polyploidy happens in animals, just not in birds and mammals so much. Fish, insects, amphibians, and others all have events early in their lineages (so it's not just a dead end when it happens)2. The failure of polyploids in mammals and birds is not a result of complications from sexual determination- This was going to be my other point for why it happens in plants more than animals, but I guess that is wrong. So their point is that problems from polyploidy aren't due to confusion in sexual identity, but rather more general developmental problems.
Quote from: another_someone on 02/11/2007 12:37:21One other aspect I think may be the case (maybe you might comment) is that the species boundaries between plants is less sharply defined than in animals, hence it is easier to cross breed between plant species than animal species. This would imply that plants are better able to tolerate alien genes (consistent with your arguments above) than animals are, but still take something useful from the alien chromosomes while suppressing anything toxic within them. This too, I believe is one of the ways in which higher order polyploidism is introduced into plants species.I wonder about this, it would certainly seem possible. It does seem that the species line is blurred more in plants- but my hesitation here is just that I am not sure how good we are at defining a "species." For example. . . if you were just looking at the wide size range of dogs, you might not think that they were the same species, but we know they are and one piece of evidence for that is that they can mate and produce viable offspring, but how about two plants that can do the same, but also look wildly different- are they the same species? The whole "what is a species" debate is tough and way out of my area of understanding - I'm not even sure some of the students here are all the same species (especially this weekend- it's the Michigan vs Michigan State home game- they are all wacko sapiens- especially the ones from Michigan!)
There is a lot more interesting in that article, I need to figure out what I can post here from it and what has copyright issues (and I need to do some work today). So this weekend I'll try to summarize some of the other cool things from the article or post them directly if allowed.
Hi George, I didn't forget about this discussion, but I have been super busy (but still thinking about it).
To get the discussion kick-started again- the warm blooded / cold blooded difference idea- seems like the real divide is between mammals and non-mammals. Is this also the divide between warm/cold blooded?
Your point about parthenogenesis makes sense, if one is not mixing the gene pool perhaps polyploidy provides a means for accumulation of mutations that allow for the maintenance of genetic diversity- I wonder if this is actively regulated?
The odd thing about this is that parthenogenesis is not very common in plants, where (as the start for this discussion) we know polyploidy is very common.