A bit dense for a light topic...
Updated: Jul 15, 2019
Hey there! This week I wanted to write about something that’s very often on my mind: plant breeding.
In the current era of CRISPR and genetic engineering, there are some very negative opinions on and around the topic. BUT, I think these opinions can be too sweeping. There are many other traditional ways in which plant breeders are working to keep developing varieties that serve farmers and ultimately our global dietary needs.
To explain that a bit better, I picked out a couple of articles that describe one avenue of crop development that I think is pretty interesting. If you’re up for a little bit of science, read on…
It probably goes without saying that photosynthesis is phenomenal. Without the light harvesting tendencies of our green companions, life on Earth would be unrecognizable at best.
(Need a quick recap on photosynthesis and carbon fixation? Check out this 3 min. overview: https://www.youtube.com/watch?v=13h5oC4jIsk)
Photosynthesis is first in the chain of events leading to carbon fixation and plant growth. With this in mind, the photosynthetic process is an excellent target for plant breeding.
Improved photosynthesis could lead to bigger plants, higher yields, and more food to go around. Additionally, a faster growth rate could help photosynthetically improved plants to grow faster and outcompete weeds, a must for organic and conventional growers alike.
To quickly clarify, there is a difference between breeding for photosynthesis and what is called “carbon partitioning.” The latter would be something like “dwarfing” grain varieties to make them shorter, which in turn frees up more energy to become actual grain. While there is more of the target material (grain in this example), there is not more energy stored in the plant as a whole. Contrarily, breeding for photosynthesis actually fixes more carbon, allowing for a larger plant overall.
The concept of breeding for this improvement is several decades old, however there has yet to be a major success. The complexity of various photosynthetic mechanisms limited any advances while information on HOW it could be done was accumulated.
There are several approaches to breeding better photosynthesis that are gaining momentum, but here are just a couple:
Breeding for more efficient Rubisco
Rubisco is an enzyme that is KEY to the Calvin cycle. Accordingly, it takes up nearly half the protein in a leaf and is a very complex, large enzyme overall. Rubisco evolved during eons of more CO2 dense periods, and so it commonly attempts to fix the O2 molecule instead. This is an energy sinkhole for a plant.
One proposed approach to working on this enzyme is to change the carbon concentrating mechanism (CCM) of the plant. These mechanisms have some diversity as a result of evolution to counter in unfortunately inefficient Rubisco. The existing mechanisms are known as C3, C4, and CAM. (Here’s where I hope you watched that video!)
There is an ongoing effort to breed rice that uses the C4 pathway instead of C3. Additionally, it has been noticed that tissues around developing grain in wheat (a C3 plant) are operating as C4. Maybe this indicates it won’t be an impossible change to make with more traditional breeding approaches.
Breeding for light response
After a certain point on a sunny day, the photosynthesizing organelles can’t use any more of the incoming energy. Since they can’t get up and move out of the sun, a process called “photoprotection” takes place. This protection is an equivalent to humans sweating on a hot day, by allowing the plants to turn extra light into heat that they let go.
Some breeding is ongoing to improve the “relaxation” of this protective process. Pretty much this means the plants are quicker to resume normal photosynthesis as soon as there is less incoming light. It’s a promising approach that has shown 15-20% increases in plant size.
With that, I’ll wrap up this dense post by pointing out something very important about all these plant breeding projects…
None of the described project are using “genetic engineering” or “genetic modification.” While the approaches are very technical and are done using all kinds of statistical analyses and microbiological work, they are utilizing DNA that already exists in the plants that are being worked on. (As a reminder, GE/GMO crops contain DNA that is taken from a different organism. An example of this was the creation of “Golden Rice” by inserting genes from daffodils into rice to increase the beta-carotene content.)
Anyways, I think this is cool work that people are out there doing, and hopefully you found something that was new or interesting it this post!
What do you want plant breeders to work on? Do these projects bother you, excite you, confuse you?
Send me your thoughts and questions about this or any other seedy topics!
Orr, D. J., Pereira, A. M., Pereira-Lima, I. A., & Araújo, W. L. (2017, October 26). Engineering photosynthesis: progress and perspectives. Retrieved from National Center for Biotechnology Information: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5658708/
Rangan, P., Furtado, A., & Henry, R. J. (2016, August 17). New evidence for grain specific C4 photosynthesis in wheat. Retrieved from Nature: https://www.nature.com/articles/srep31721