STiR coffee and tea magazine

26 STiR coffee and tea / Issue 3, 2017 (June/July) Evolutionary differences of three important metabolic pathways (caffeine, flavenols, and theanine) associated with tea-pro- cessing suitability and quality among the 25 Camellia species. Tea is under threat. We already know much about the threat of climate change to staple crops such as wheat, maize, and rice, but the impact on tea is just coming into focus. Early research indicates that tea grown in some parts of Asia could see yields decline by up to 55% thanks to drought or excessive heat, and the quality of the tea is also falling. The intensive use of pesticides and chemical fertilizers in tea plan- tations has also led to soil degradation at an average annual rate of 2.8%. This also causes chemical runoff into waterways, which can lead to serious problems for human health and the environment. However, hope may be on the horizon now that scientists at the Kunming Institute of Botany at the Chinese Academy of Sciences have sequenced the entire tea genome. Mapping the exact sequence of DNA in this way provides the foundation for extracting all the genetic informa- tion needed to help breed and speed up development of new varieties of the tea plant. And it could even help improve the drinks flavour and nutritional value. In particular, the whole tea tree genome reveals the genetic basis for teas tolerance to environmental stresses, pest and disease resis- tance, flavour, productivity and quality. So breeders could more pre- cisely produce better tea varieties that produce higher crop yields and use water and nutrients more efficiently. And they could do this while widening the genetic diversity of tea plants, improving the overall health of the tea plant population. This is also an important milestone for scientists because it provides a deeper understanding of the complex evolution and the functions of key genes associated with stress tolerance, tea flavour and adaptation. Mmm, you can really taste the flavonoids. The tea genome is very large, with nearly 37,000 genes, more than four times the size of the coffee plant genome. The process of evolution by natural selection has already helped the tea plant develop hundreds of genes related to resisting environmental stress from drought and disease. These genes are like molecular markers that scientists can identify when selecting plants for use in breeding. This will allow them to be more certain that the next generation of plants they produce will have the genes and so the traits they want, speeding up the breeding pro- cess. Sequencing the genome also raises the possibility of using ge- netic modification (GM) technologies to turn on or enhance desirable genes (or turn off undesirable ones). The same principles could also be used to enhance the nutritional or medicinal value of certain tea varieties. The genome sequence in- cludes genes associated with biosynthesis. This is the production of the proteins and enzymes involved in creating the compounds that make tea so drinkable, such as flavonoids, terpenes, and caffeine. These are closely related to the aroma, flavor, and quality of tea and so using ge- netic breeding techniques could help improve the taste of tea and make it more flavourful or nutritional. For example, we could also remove the caffeine biosynthetic genes from the tea plant to help breeding of low or non-caffeine varieties. By boosting certain compounds at the same time, we could make tea healthi- er and develop entirely new flavours to make caffeine tea more appealing. An estimated 5.56 metric tons of tea is commercially grown on more than 3.8 million hectares of land (as of 2014). And its huge cultural importance, as well as its economic value, mean securing a sustain- able future for tea is vitally important for millions of people. So the first successful sequencing of the tea genome is a crucial step to making tea plants more robust, productive and drinkable in the face of massive environmental challenges. Chungui Lu is professor of sustainable agriculture., Nottingham Trent University. This article was originally published on The Conversation. DNA Mapping of Tea Could Stave Off a Pending Crisis By Chungui Lu tolerance, and horizontal leaf poise for mechanical harvesting," Gao explains. "Earlier work in my laboratory has enabled us to identify 10 RAPD markers (each only 10 base pairs long) asso- ciated with desirable tea traits, e.g. black tea quality, high yield, drought, cold, fungal, and insect. 1 "We are currently busy with the bioinformatics analysis of 12,000 DNA markers (each only 69 base pairs long) that we hope will associate, to some degree, with desirable tea traits. The publication of the tea genome will enable us to determine which of our markers occur in genes that form parts of proteins, and the biochemical pathways in which these proteins operate that could be associated with the desirable tea traits. Once we know which of our markers are closely associated with the desirable traits, we will be able to score potential parent trees for these markers and select very good parents for breeding the next gen- eration of tea trees. By careful selection of tea parents, we will be able to breed new tea cultivars with the desirable traits. It will probably still take 15 years to breed and select the new cultivars, but we will be able to breed designer-cultivars for e.g. high or low caffeine or any other trait. This information will also enable us to breed new cultivars with combinations of more than one traits, e.g. fast fermenters for black tea, that are high in health promoting antioxidants (catechins), that have high yield and are drought and cold tolerant, with good aroma and horizontal leaf poise," he writes. In the US Dr. Guihong Bi, a colleague of Prof. Broderick at Mississippi State University, along with several collaborators is working to develop tea as a specialty crop on the US mainland. "We have submitted a grant to further develop growing methods for tea and to measure the diversity of our collection, which includes cultivars from many regions," said Broderick. "Once we know that we have a good collection and know a little bit about their performance, we can start to make mapping populations and identify accessions that perform well under 1NIK Mphangwe et al 2013 (Appl Biochem Biotechnol (2013) 171:437–449, DOI 10.1007/s12010-013-0370-4).

• Cover