The genome of the shrub Camellia sinensis has been published for the first time. If that doesn't sound exciting to you, perhaps you are not aware that Camellia sinensis gives us our most popular types of tea, a product essential to the happiness of billions, and a substantial part of the global economy. Understanding the genome could explain how one plant produces such diverse flavors, and could even help produce even richer and more robust plants.
Professor Li-zhi Gao of China's Kunming Institute of Botany, found the genome of Yunkang 10, a tea cultivar popular in southwestern China, is packed with “jumping genes”, more formally known as retrotransposon sequences. These are genes that move around the genome, turning up multiple times in different places, and altering the expression of genes nearby. In fact, two-thirds of C. sinensis' base pairs are jumping genes. The tea genome is also heavy with genes for pathogen defense, reflecting the diverse environments in which it has had to survive.
Considering tea's economic and cultural significance, it's surprising the genome has not been sequenced before. Could any self-respecting citizen of Britain, India or Japan seriously prioritize the sequencing of the black cottonwood tree genome over the plant responsible for black, green, and white tea?
The Camellia genus contains 119 species, some of which do useful things like look nice and provide oil, but it is only the assamica and sinensis varieties of the species that are grown commercially for drinking. “The mystery is what determines or what is the genetic basis of tea flavors?” said Gao in a statement.
Tea's flavor comes primarily from flavonoids, a type of anti-oxidant. Like caffeine, flavonoids are produced by proteins in the tea plant's leaves, so the genes that code for those proteins are ultimately responsible. It appears the jumping genes have made possible the diversity of gene expression, explaining why different varieties of tea from closely related plants taste so different.
The astonishing quantity of jumping genes also explains why less commercially important plants were sequenced before C. sinensis. “Our lab has successfully sequenced and assembled more than twenty plant genomes,” said Gao. “But this genome, the tea tree genome, was tough.” It took five years for Gao to publish in Molecular Plant and there are still many varieties unsequenced that could shed light on how the genome has changed in response to cultivation in different environments.
Tea drinkers who like to look down on coffee enthusiasts will be pleased to hear their preferred plant has four times as many base pairs (3 billion, similar to humans). The large genome size alone slows the sequencing process, but the number of duplicates is worse, making it very hard to work out what goes where.
Did you know black, green and white tea, along with some other types, all come from the same species? And it has quite pretty flowers. Li-zhi Gao