Page 317 - AWSAR 2.0

G-guanine, C-cytosine and T-thymine (or U-uracil in RNAs, a related nucleic acid). The entire length of DNA is chains of these four bases arranged in a specific order (the number of such ATGCs in rice is whopping ~420 Mbp, that is, 420,000,000 base pairs, which are comparatively smaller than many other organisms!) hidden deep inside the nucleus of every cell. A gene is a small part of the DNA, and every organism has thousands of genes to control their day-to- day activities. One important thing to note here is, a simple change in the order of these nucleobases, or insertion or deletion of one or many nucleobases, can completely modify the behaviour (or “expression” as it is called) of the genes. For example, human beings and chimpanzees have just 1.2% variation at the DNA level. Modern methods have enabled us to artificially modify the DNA bases with the help of many tools. One may wonder to find that these tools are not against
natural laws but are highly
established mechanisms found
in bacteria and certain viruses.
One such recent find that is revolutionizing every field in
life sciences is CRISPR. This
CRISPR, in association with
an enzyme called Cas9, is an
inherent defence mechanism
found in bacteria and archaea,
protecting against the viruses
that attack them. They work
wonderfully as follows: CRISPR is a short repeat sequence of DNA that is memorized by the bacteria from the virus DNA. So the next time the villain arrives, the bacteria simply send the Cas9 which identifies the virus by reading the sequence and selectively demolishes the viral DNA by cutting them into pieces. Scientists at the University of California Berkeley and Broad Institute, Boston have found that with small modifications, these enzymes can be
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engineered to cut the DNA of any organism making genome engineering very easy and affordable.
In our research, we are developing a superior rice plant which could be useful for increasing the rice yield up to 30% by making it suitable for developing hybrid varieties. Coming to hybrids, these are the offspring of a mating between a male and a female. Human culture, for example, encourages marriage between distant relatives so that the babies would be strong and disease-free. Similarly, in cultivated rice (Oryza sativa), even though they are self-pollinated, crossing between different varieties could positively increase the vigour of the plants especially the grain yield. However, in nature, it occurs less than 5% since the self-pollination occurs even before the opening of the rice flower. To avoid this, we need to manually remove the male part of the rice flower the anther, just before
the maturity and dust with the pollen of another variety. Since every rice plant has hundreds of flowers, manually removing them is simply impossible.
Again, nature has gifted us with another clue, which is “male sterility”. In some wild relatives of rice, the male part of the rice flower is simply non- functional. Another wonder is that these can revert to male fertility when grown under lower
temperatures (say, below 25 °C) and above 25 °C, these are sterile. Scientists have named it as “thermosensitive genic male-sterile”. This property allows commercial growers that when male-fertile plants (a male parent) are raised near the male-sterile plants (a female parent), it is easy to cross and produce hybrid seeds. China, with its largest population in the world, relies almost 90% on such hybrid rice varieties to feed its people.
The population growth is burgeoning at such a rate that the Food and Agricultural Organization says we need to increase the food production by 70% before 2050.