Variations in climate can cause genetic diversity in plant populations

A new paper in Science highlights how variation in an environment can mean plants have no single solution for survival. Where conditions change, genetic diversity can be the best option for a species.

We talk of plant species as though the individuals are more or less the same. However, their genes can hold the potential for diverse responses similar environments. Why? If a plant lives in a specific location, why doesn’t it find the best solution and home in on it. Research in Science says that the reason plants have genetic variation is partly due their environments varying.

Seep monkeyflower, Mimulus guttatus
Erythranthe guttata or Mimulus guttatus in Icicle Canyon, Chelan County Washington. Photo: Thayne Tuason / Wikipedia

Troth and colleagues looked at how Seep monkeyflower, Mimulus guttatus, behaved. Effectively it has a simple choice grow big or small. If it grows big, then it can make more seeds and have more chance of offspring. Given a choice, the best option seems simple. The problem for Mimulus guttatus is the local environment.

Mimulus guttatus grows in western North America, and when it grows it’s in a race against the sun. It’s an annual flower, so it has to germinate, grow and set seed in one season, and the season ends with the summer drought. Spend too long growing and you lose your chance to seed. But growing fast to beat the heat means you set fewer seeds and could be out-competed by your rivals.

To find out what was going on Troth’s team went to the Iron Mountain in Oregon. They took samples and created 187 inbred lines of plants, and then sequenced them to look at their genomes. What they were found was that the plants could have variations of a gene, an allele, that could delay flowering. These same alleles also made the plant grow larger, something Troth and colleagues identify as “antagonistic pleiotropy”, pleiotropy being where one gene can influence two completely different traits. It means a plant adapted for one future is at a disadvantage, if it turns out differently. So while small and fast is usually the best strategy at Iron Mountain, when conditions change large and slow wins, and wins big. The result is that alleles all get swapped around when conditions switch.

Daniel J Kliebenstein noted on Twitter that environment isn’t the only thing to shift. His research in Arabidopsis thalania shows that pathogens and fluctuation in herbivore populations can also change selection pressures at the same location.

The need to respond to dynamic changes in a location, also affects studying what Murchie and colleagues call the ‘photosynthome’, the traits that affect how a plant manages its photosynthesis.

Troth’s work emphasises that while plants might be static, their environoments aren’t and being able to cope with whatever nature throws at you is going to take a lot of genetic resources.

Further reading

Troth, A., Puzey, J.R., Kim, R.S., Willis, J.H. & Kelly, J.K. (2018). Selective trade-offs maintain alleles underpinning complex trait variation in plants. Science, 361 (6401). pp. 475-8. https://doi.org/10.1126/science.aat5760

Kerwin, R., Feusier, J., Corwin, J., Rubin, M., Lin, C., Muok, A., … Kliebenstein, D. J. (2015). Natural genetic variation in Arabidopsis thaliana defense metabolism genes modulates field fitness. eLife, 4. https://doi.org/10.7554/eLife.05604

Murchie, E. H., Kefauver, S., Araus, J. L., Muller, O., Rascher, U., Flood, P. J., & Lawson, T. (2018). Measuring the dynamic photosynthome. Annals of Botany, 122(2), 207–220. https://doi.org/10.1093/aob/mcy087