What Knowing the Tea Tree Genome Means to the Flavors in our Cup
Dr. Virginia Utermohlen Lovelace
By Dr. Virginia Utermohlen Lovelace
One of the most remarkable aspects of C. sinensis is how it has managed to find a niche and thrive on every continent except Antarctica. The publication of tea tree’s genetic code* by scientists at the Kunming Institute of Botany in China gives us critical clues to its hardiness and tastiness.
The tea tree in question was a Camellia sinensis var. Assamica, grown in Yunnan Province, China. After they figured out this DNA code, they were able to look into the codes of a number of other Camellia cultivars, and compare these codes to those of other plants.
As we all know, plants can’t run away from danger, so they develop chemical strategies to deal with both disease and environmental changes. These chemical strategies yield the compounds that not only help the plant survive and reproduce, but also provide the flavor we enjoy in the cup.
Chemical strategies are dictated by the plant’s genes. The larger the number of defense genes, the larger the repertoire of strategies, and the better the plant can endure attacks and thrive. It turns out that tea trees have a huge genome (as the collection of genes in an organism’s DNA is known). It has about 36% more genes than coffee plants, and 19% more genes than cacao!
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The tea tree’s huge genome comes from duplication of portions of the plant’s DNA, coupled with two rounds of duplication of the entire genome over the course of the past 60 million or so years. Normally plants (and animals, too) have the ability to weed out mutations and errors in the DNA copying process, so that when duplications occur, they may be removed in whole or in part. It seems that the tea tree is inefficient at pruning its DNA. The result: its enormous genome, particularly enriched in duplicates of genes that give us caffeine and catechins, the bitter compounds in tea; L-theanine, which imparts a savory/sweet quality to tea; and terpenes, which give teas their aromatic qualities.
While we enjoy the results of this gene duplication process in our cup, the tea tree enjoys it through survival in a wide range of environments, wider than that of either coffee or cacao trees. The catechins, for example, serve as a sunblock, while caffeine, L-theanine, and terpenes can deter insects. Importantly the more copies of the genes for making these compounds a Camellia plant has, the greater the amount of these compounds produced, and the healthier the tree remains.
Which brings me to yet another aspect of the discovery that is so important for understanding tea. If you have ever wondered why the tender leaf shoots most often provide the most flavorful teas, the authors provide the biology behind the answer.
But first, you should know that each cell in a tea leaf (and in our bodies, too, and in every multicellular organism) has a complete complement of genes. What distinguishes individual cells is the activity of the different genes. For example, in ourselves, the ability to make odor receptors is turned on in our olfactory tissue, while the stomach you get cells making digestive enzymes.
The authors of the study explored where in the plant genes were turned to produce catechins, caffeine, and L-theanine. Gene activity for the production of L-theanine was the same in all parts of the plant, but gene activity for the production of caffeine and catechins was highest in “tender shoots” and seeds. If you think about it, the results are not really surprising: the tender shoots are the most vulnerable part of the plant to sunburn (resisted by catechins) and insects (resisted by caffeine and a host of other compounds). This observation supports our preference for first flush tippy teas.
Researchers armed with this genetic information can now begin a systematic exploration at the molecular level of wild relatives of cultivated tea. They can search for variants with specific properties. With luck, such an exploration will lead to development of desirable characteristics in cultivated trees, and slow down the over-plucking that is leading to the decline of precious wild trees.
Virginia Utermohlen Lovelance, MD is the author of Three Basic Teas & How to Enjoy Them. Virginia retired as a faculty member in the Division of Nutritional Sciences at Cornell University, Ithaca, New York. Learn more: www.pairteas.com
*Citation: Xia et al., The Tea Tree Genome ProvidesInsights into Tea Flavor and Independent Evolution ofCaffeine Biosynthesis, Molecular Plant (2017)