STiR coffee and tea magazine

24 STiR coffee and tea / Issue 3, 2017 (June/July) T By Dan Bolton Unraveling the Tea Genome en commercial tree crop genomes have been published since 2000. Apples, apricots, pears, grape, papaya, and peach trees were the easy ones — and they took years. Cacao was sequenced in 2013 and robusta coffee in 2014. The pace has since quickened. The first public genome sequence for Coffea arabica, the species responsible for more than 70% of global coffee production, was released in January by researchers at the University of California, Davis. It was high time for tea. In May a team of 29 Chinese scientists from 12 research institutes in China, South Korea, and the United States, pub- lished their findings in the journal Molecular Plant. They describe a remarkably complex DNA that at one point during the plant's long evolution doubled in size. Researchers selected the Yunkang 10 cultivar to study, it is an assamica cultivar growing in Yunnan. The task was made difficult because tea over eons has learned to duplicate benefi- cial sequences. The plant experienced two "whole genome du- plication" events in the past 50 million years equipping it with greater disease resistance, the ability to cope with stress brought by drought, tolerance to heat, and the ability to identify and deal with pathogens within its self. Professor Zeno Apostolides in the department of biology at the University of Pretoria, South Africa, expressed delight at the news. "I expect that a flurry of scientific publications will follow, in the next 15 years, describing cultivars of tea with improved yield, increased tolerance to insect pests, fungal and bacterial diseases and drought," he said. (See, DNA Mapping of Tea Could Stave off a Pending Crisis, pg 26) "The tea genome will also allow breeding of new cultivars with unique flavours, e.g. low or high caffeine for different mar- ket segments, slow fermenters for green tea, fast fermenters for The tea plant contains three billion base pairs of DNA, four times more than coffee or cacao. It took five years to unravel but the first high-quality map of the genome was published in May. Now it's time to get to work coming up with practical applications of the tea genome for commercial tea production. black tea, high theanine for the umami taste or high catechins for health properties. The achievements will be made possible by classical breeding and selection, without any genetic modifi- cation of the tea plant," he said. (See, What Knowing the Tea Tree Genome Means to the Flavors in Our Cup, pg 28) The process "Sequencing capabilities have exploded in the last decade mak- ing it much cheaper and faster to generate genetic sequences," writes Professor Shaun R. Broderick, assistant research/exten- sion professor of ornamental horticulture in the department of plant and soil sciences at Mississippi State University. "Most sequencing technologies require that DNA be frag- mented into small pieces before sequencing," Broderick said. "These short sequences are then strung back together using computer software. The tea genome is about the same size as the human genome, but tea DNA doubled at one point during its evolutionary past, meaning that there are at least two copies of every gene. It's like trying to put together a puzzle where ev- ery piece has a nearly identical matching piece. On top of that, the puzzle has hundreds of millions of pieces. It is exciting to see this technology develop to the point that researchers can now solve puzzles that are this complicated. "Sequencing the tea genome will allow researchers to more easily answer questions about where tea plants originated and their breeding pedigrees. We can use it to help us identify the genes that control heat tolerance, cold tolerance, disease resis- tance, flavor compounds, secondary metabolites and yield. Al- most all genetic research in tea will be made easier and faster. In many ways, we can use it to direct breeding and genome editing efforts to produce improved cultivars that don't require as much This diagram shows how the tea tree genome evolved in relation to similar plants

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