Sunday, March 9, 2008

Things I learned in Canberra

First, there is mitochondrial DNA.

All eukaryotes have mitochondrial DNA.
This DNA codes for things that are useful in mitochondria.
This set of things, however, is different across different species.

Over all species, however, there is not one thing useful in mitochondria that is not coded for in nuclear DNA.

Second, I learned that there is extremely good evidence for transposons acting to transfer a beneficial characteristic from one species to another- specifically, to transform an inert species of fungus into a wheat pathogen. I always thought this sort of thing was a theoretical possibility, but I had never heard any good evidence of it happening in eukaryotes before. Voila, it happens!

Third, I learned that I need to learn a lot more about plants.

Green plants are more complicated then us. They have larger genomes, on average, and have chloroplasts with their own DNA as well as mitochondria with their own DNA. They make an awful lot of things that we have to get by eating other things, so they have more complicated metabolic pathways. Our sense of how natural selection works is also skewed by us usually thinking of animals rather than plants, despite all that rigmarole with peas back in Mendel’s time: one animal individual crosses with one other individual to make some offspring. But consider your typical tree, covered with gazillions of flowers: it is more like one individual crossing with the whole population within ever so many kilometres to make some offspring. Actually, don’t a lot of animals in the ocean do the same sort of thing?

I learned specifically that I need to learn more about the immune system of plants. It seems plants have no acquired immune system. Each plant cell is autonomous, and just has the genetic potential for immunity that it started out with. A plant can’t acquire antibodies to something new and strange the way we can. (Memo to self: how do we actually do this, again? I need also to revise what I sort of kind of once knew about the immune system of us.) You would think, without any acquired resistance, plants would need a rapid turnover of generations to have any chance of adapting to pathogens. Sure, a lot of plants do seem to have a rapid turnover of generations. Yet, we have these things called trees that live for hundreds or thousands of years. How do they do it? They are likely to be facing a completely different pathogenic environment at the end of their lives than at the beginning. They are supposed to have no more resistance than what they were genetically programmed with.

Action: Learn about the molecular biology and evolutionary biology of plants. It is interesting.

I ought to point out that Marco's thoughts about evolution were rattling about in my head while I was learning these things.

1 comment:

Jenny said...

Aquatic invertebrates also have weird immune systems that lack adaptive immunity - it drove one of the students here nuts when she sent papers in and the comments went "why didn't you just do X" Apparently a lot of mammalian immunology people don't get that aquatic invertebrates are weird and don't have X.