biology Genetics Plants

Of course plants are more genetically complex!

Let’s remember back to a time before the human genome project published it’s first draft assembly in 2001. The genome of C. elegans a tiny nematode had already been published with ~20,000 genes. The C. elegans genome is one 1/30 the size of the human genome and the tiny worms are so small that biologists have mapped the developmental fate of every single cell in their bodies (an adult C. elegans has exactly 959 or 1031 cells depending on gender), whereas the human body contains tens of trillions. How many genes would you guess humans have?

Estimates at the time ranged from 40,000 to 150,000 genes. Then the draft genome was published and estimates drop to 30,000-40,000 range. The final genome paper comes out and estimates drop even further. Fast forward to today and the latest annotations show the human genome contains a mere 23,000 genes. I’m sorry. I know we want to feel special, the very pinnacle of evolution.* But at least when it comes to gene count, we’re not. If comparing our own genome to that of Arabidopsis thaliana (the first plant genome to be sequenced, contained 27,000 genes) didn’t drive that home, the second plant genome sequenced, rice, with its 40,577 non-transposon related genes surely made the point.

Yet somehow every time a new plant genome comes out, as the corn genome did this week, it’s big news that it has more genes than our own. Maybe this is partially because journalists have trouble understanding the true impact of this research and it’s an easy fact to latch on to. But I think at least part of it is that we still take it personally that our genomes don’t respect our special-ness as a species.

If it makes you feel any better, think about it this way. Plants have to observe and react to their environments intelligently in order to survive. So does every living thing. But plants don’t contain a single nerve cell. They can’t learn. edit: (with some caveats see the comment section). Every aspect of every reaction to every stimuli, from lack of water, to out competing neighbors, to an excess of boron (yes, there are people who study genetic variation in plant’s ability to survive in high boron soils) must be hard coded into their DNA. It’s one of the big reasons I love studying plant genomics. Everything about a plant is in there, we just have to know enough to understand it. (Though my hard learned advice is not to spend too much time talking about how wonderful it is not to have to worry about cognitive science and neurobiology when dealing with people who work in animal systems.)

*Nevermind that evolution doesn’t actually have a pinnacle just countless branches.

2 replies on “Of course plants are more genetically complex!”

James, thanks for the great blog (I just started following a few weeks ago). Just wanted to point out that plants do have learned responses. Arguably, anti-viral RNA silencing is the plant analogy of acquired immunity.

Thanks for the catch! I can’t believe I forgot that. I believe there are also some vernalization-type responses that could be viewed as memory.

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