Crazy plant genetics

Although I’m not usually that keen on genetics, I can’t but be mesmerised by the awesome genetic ability of plants.

Since my genetics class before university was mostly focused on animals, I tended to forget that, being so different to animals at the anatomical and physiological level, plants are something else entirely in terms of genetics too.

I repeat: genetics is not my thing. Therefore, I will not have the confidence to go into any detail here, but if this grabs your attention – which I hope it does – it would be fun if you tried out my tips for researching, in a recent post.

First of all, plants are experts at asexual reproduction, i.e. cloning themselves, sort of like most bacteria and other unicellular organisms do, but more complicated. A perhaps familiar example of how they do this is vegetative propagation, basically spreading out underground roots wherefrom new plant individuals bud out. This ability helps them to quickly colonise a new area.

Now, I know for myself that I would instinctively think that cloning does not have much to do with genetics, since it is just making a copy of everything. The genetics we learned about in class was all about sexual reproduction, which is mixing genetic material from both parents into an offspring and how that works.

Cloning sounds simple in comparison. However, at university, we have learned quite a bit about gene activation – different genes being turned on at different times. This is crucial for animals, since our bodies change as we age: some genes are turned on early, others later, and some are turned off after a certain time. But, try to imagine the gene activation mechanism required for creating a clone of a complex, multicellular organism. In animals, the offspring starts from zero, (mostly) unattached to the parents, whereas the plant clones literally grow out of their parent, which is already developed enough. I may just be wrong, but I think that the clones quickly catch up with their parent in development, which means their gene activation sequence must be different. (They are clones in the sense that they have the same total set of genes – the same genome – but the way these genes are activated is what determines what the individual will look like, so if they are used differently, the clones can become radically different, or, in this case, similar even though they should be at different developmental stages. In basic genetic jargon, we would say the clones have the same genotype, but may have different phenotypes, whereas in this case, they would be expected to have different phenotypes, but they purposefully don’t.)

Plants are of course also able to reproduce sexually, which is how they adapt to their environment in a selective way, rather than by random mutation. A mutation is a spontaneous change in the genome of an organism. Some are quite familiar to us, such as the trisomy 21, or three copies of chromosome 21, in humans, which causes Down’s syndrome. I mention this mutation in particular because it shows that mutations are not limited to some gene bases being copied wrong, resulting in a different protein, but also includes accidents in cell division, where the genes may not have separated as they should. In trisomy 21, of the four copies of chromosome 21 that are meant to split evenly into the four sperm cells, a par did not separate, so one sperm ended up with two, and another one without a chromosome 21. If the sperm with the extra chromosome 21 enters the egg, which has its own copy of chromosome 21, the foetus will most likely develop trisomy 21.

This example results in an unfortunate condition for the child, but some of these mutations can work wonders. Most big leaps in evolution are thought to have been caused by large (and lucky) mutations of this kind.

While such crazy genetics can cause harm, or, as in most cases, prevent the zygote (fertilised egg) from developing at all, or maybe not have any effect at all, on the rare occasion, it produces something entirely novel. The Cambrian explosion, an event in the very early stages of animal evolution, saw a myriad of radically different animals emerge, so different from one another that the experts have no clue of how to classify many of them. It might have been full of such mutation events. (Hadn’t thought of that until writing this post actually, but it has given me something to think about now!)

In plants, at least two radical mutations of this sort have marked the rise of a whole new type of plants, which today dominate the flora. These mutations were even more crazy than getting and extra chromosome, though: they experienced a whole-genome duplication, i.e. a doubling of all chromosomes, all genes. I doubt any animal species would survive this, at least not with fertile offspring that could spread it to following generations – but plants did this twice, and moulded it into their perhaps greatest evolutionary inventions! I think they deserve an applause for this!!

The first whole-genome duplication event in plants occurred in the Late Carboniferous (Pennsylvanian), about 320 million years ago, and resulted in the emergence of seed plants, i.e. plants which encase their sexually produced offspring in a protective capsule, the seed, with enough moisture and nutrients to be able to lie dormant (‘inactive’) in the soil for long periods of time, enabling them to survive dry seasons and wait for optimal conditions before germinating into a seedling. The seed was perhaps the key innovation that freed the seed plants from their reproductive dependence on stable water bodies, and enabled plants to colonise land completely. Prior to this event, plants were only able to live by coasts and around nearby lakes, and, thus, animals were equally limited. The advent of seed plants enabled life to break free from the sea and move further inland, bringing complex life to all corners of the Earth. It turned out to be one of the most significant cornerstones in the history of life on this planet. How awesome isn’t that?!

The second time this happened, in the Early Jurassic period, roughly 190 million years ago, the world saw the first flowering plants, or angiosperms. (However, I remember reading a very recent article where scientist have found angiosperm-like pollen dating as far back as 240 million years ago, which is the Middle Triassic, so maybe this whole-genome duplication marked the emergence of more awesome angiosperms, or perhaps the dating methods are inaccurate.) The flowering plants are hugely important for us animals, since their strategy of recruiting animals to spread their seeds and pollen, helping them reproduce, means that they must be generous in providing nutritious rewards in the form of fruits and vegetables. (We also eat some of their seeds and roots, which the plants are not as happy about…) In other words, the flowering plants provide much better food for herbivores, which brings more easily available energy and nutrition to the food chain.

I have not yet read the paper about these whole-genome duplications, which I found ages ago, so I cannot give you much details. However, I am excited to learn more now, and I might just add another entry about this later. I hope it inspired you too. Respect plants!