The crops whose products we happily eat are derived from wild ancestors through thousands and thousands of years of breeding. This has delivered the high yielding varieties whose high-end products we now find in many of
our local stores, and that hardly remind us of what their ancestors looked like. Maize, for example, was derived
from teosinte after initial cultivation in Mexico; a grass that delivered no more than a few small grains per ear.
In the 1930-60’s agriculture saw the introduction of semi-dwarf varieties of for example wheat but also many other
crops, which sparked an incredible rise of yield. The logic behind this aspect of the so-called Green Revolution was
quite simple: Investments that plants typically made in stem growth, were minimized and used to produce
harvestable material, which most often are the plant’s seeds;.
The need for improved varieties has not changed, but substantial emphasis is now on crops with increased
tolerance to abiotic and biotic stress factors. This is achieved by selecting for phenotypes with preferred
properties, for example high yield, and is encoded in their DNA. Obviously, many crops are continuously improved
to resist diseases, an arms race between breeders and pathogens. An inspiring example of breeding for abiotic
stress resistance came from rice that, like most other crops, dies after prolonged complete floods. Scientists from
University of California and the International Rice Research Institute identified a gene from a well-known
submergence-tolerant variety of rice. The gene was found responsible for the fact that the plant uses a minimum
amount of energy while submerged. A strategy that we call energy-conserving quiescence; it’s just waiting out the
bad times with a minimum energy loss. However, the rice variety in which this gene was found was very tall and
yielded small amounts of product; the rice grains that we eat. Therefore this energy-conserving gene, called
submergence-1A, was introduced into high-yielding, semi-dwarf varieties, through marker-assisted backcrossing.
This was done successfully and without obvious yield penalties. These new varieties are now widely used in many
Asian countries, including India, Philippines and Indonesia. The picture shows the dramatically increased tolerance
for submergence that these sub1 lines possess.
Also animals, like salmon, have genetically determined properties that help them deal with their environment.
However, there is room for improvement. Wild Atlantic salmon reproduce in rivers in the fall/early winter. The
young fish hatch in spring and spend their early life in rivers. After going through a development called
smoltification, they can survive in seawater and enter the food-rich ocean, where they grow rapidly but remain
sexually immature. Only after having reached a sufficient body mass, puberty is initiated. With puberty, sex steroid
levels increase and trigger a change back to being able to survive in freshwater. This prepares the fish for the
migration back into rivers for reproduction.
Salmon are cultivated in sea cages, but they can only tolerate sea water until puberty. In salmon, puberty kicks in
1-2 years earlier in males than in females, so in aquaculture this is mainly a problem in males. A farmer must
harvest these maturing males long before they have reached the optimal size. Another important aspect is that
when sea cages get damaged, for example in a storm, farmed fish can escape. When they are fertile, they can
introduce their genes into wild populations, which is a risk factor for wild populations.
Studies in zebrafish identified a gene called dead end that is required for the survival of germ cells in the embryo.
Germ cells are the cells that produce sperm or eggs. When this gene is lost, germ cells are lost and the fish are
sterile. The gene functions in the same way in salmon, and it is possible to make sterile salmon using genetic
modification. This eliminates the danger of mixing genes with wild populations. Importantly, the gonads of these
sterile fish also do not produce sex steroids, so they can stay in seawater and continue to grow.
However, genetically modified fish cannot be used as food in Europe. Therefore, the plan is to vaccinate female fish
with anitbodies agianst the dead end protein. Salmon are immunized anyways against a number of diseases and
immunization against dead end could be included. Since the antibodies present in the blood of immunized fish will
block protein function in the early embryo, it will induce sterility and consequently puberty.
So by disturbing the function of a specific gene we can solve problems related to changing environmental
conditions, such as the salinity of the water.
