As a farmer, plant breeder and seedsman, my primary focus over the last 30 years has been the genetics and specifically the genome of food plants. I’ve worked with tomatoes, chile, beans and corn, developing new varieties by crossing and recrossing existing strains and wild relatives.
I think we have all had the experience of planting a variety of tomato or pepper on the advice of a friend and seeing that it does poorly in our garden. Almost always, it is worth replanting the next year either with the original seed or that saved from the previous season. I have done both, side-by-side and noticed the saved seed does better whether the seasonal conditions are similar or not.
This adaptation to the micro-climate is the result of a type of epigenetics. While the underlying genome is no different, how that genetic information is used (expressed) is different in the two plants. One has stored information on the previous growing season, the soil, available light, warmth, and the microbial populations. In a sense, the plant learned and passed that memory down to the next generation. For example, a pepper plant grown during a hot, dry summer will have smaller, narrower leaves and a different root structure that one grown under more ideal conditions. Its immediate progeny will as well.
Sections of DNA can be switched on or off resulting in the production of different proteins and enzymes. This is how, during human development, a whole variety of cells emerge, skin cells, muscle cells, liver cells, and so on. All have exactly the same DNA, but very different functions.
The process is accomplished by changing the electric potential at points along the genetic strand. This enables the transcription of certain sections rather than others. I won’t get into the exact molecular substitutions -methylation, etc. here. That is best read up on separately. However, some of these changes (not all) are inheritable. The changes not only are duplicated as cells divide and the organism grows, they are transferred to the germ line cells.
For the plant, I described this as a type of memory, which is accurate (it turns out memories in our brains are laid down using an analogous method). The advantage to the plant is a pre-programmed response to expected environmental conditions. Plants are very good at this because they can’t move to change their environment. They taste the surrounding world and adapt to it.
I’ll give an example with which I am familiar. In Northern New Mexico every village and often individual families, save chile seed down through generations. The strains (cultivars or land-races) are named after communities like Chimayo and Alcalde and Puerta de Luna. There are slight genetic differences between them and all are different from the commercial cultivars grown in Southern New Mexico. I have spent a lot of time tracking down varieties from these traditional communities. There is tantalizing variation in flavor, aroma and heat, along with differences in the shape and size of pods and the plant habit.
There is also controversy surrounding this collection. On one hand, we may wish to preserve the genetics of these crops before they disappear. It is important that diversity in food crops not be lost. On the other, traditional communities, particularly Pueblo communities, see the chile as part of their heritage, integral to who they are, and the collection as theft. The dispute may be resolved by asking a simple question.
Is the Chimayo chile grown, say in Las Cruces, the same as the chile in Chimayo?
The answer is that the plant begins to diverge immediately because Las Cruces is not Chimayo and those changes are passed down to subsequent generations. Even though the genotype has not changed, the phenotype has. Out of it’s native environment, it is a different chile. If you were to grow a number of different land races in the same field, you would not be testing each one’s eventual suitability as a food crop as much as how closely the current epigenetic landscape of each matches the new environment. Given a few generations, they will all converge on the best answer.
Next: Epigenetic Priming