Tea-drinking is a constituent part of Chinese culture. China is an original producer of tea and is renowned for its skills in planting and making tea. Hangzhou has a unique type of climate which provides adequate humidity and warmth, forming a perfectly suitable environment for a variety of tea plants to grow, and has been famous for tea production and exportation ever since Tang Dynasty. And with the hundreds of years of development of tea production, tea culture has also evolved into a unique highlight of Hangzhou. For instance, the legends and anecdotes related to tea, Tea Ceremony, and so on. They all contain the wisdom of oriental philosophy.

With the production of tea, a huge challenge confronts today’s tea farmers: pests. Nowadays a wide range of pests has been observed in the growth span of a tea plant, in which Ectropis obliqua, Empoasca flavescens, Toxoptera aurantii, etc., are regarded as the major contributors to the insect attack the tea plants would suffer from. Among them, Toxoptera aurantii, a kind of insect of Homoptera also known as tea aphid, is one of the most destructive pests in tea plantations in southern China. In addition to harming tea plants and oil tea, it also do damage to citrus, litchi, bananas, etc. Hence, tea aphids are selected as the main target we're going to work on.

Currently, climate change and the rapid evolution of insect resistance make pest control increasingly difficult. Conventional methods in tea pest control include slime boards, pesticides, etc. Another method is to use sex pheromones in pest control. Sex pheromones act as a signal to attract potential mates over long distances, and if the sex pheromones are distributed manually and properly, it could cause mating disruption(MD) thus declining the mating rate of tea pests. However, these methods not only cause pollution by direct emitting or high dependence on chemical production, but also demand plenty of manual work.

Aiming to cope with these issues and innovate automated ways to effectively decline the number of tea aphid, we turn to synthetic biology methods to seek for promising solutions.

Like other plants, tea plants use volatile chemicals as signal molecules to convey information, and of course they have corresponding receptors. Specifically, when a tea plant is attacked by piercing-sucking mouthparts pests including tea aphids, it releases a mixture of volatile compounds with benzaldehyde taking its major part. If a kind of sensitive specific benzaldehyde receptor and its corresponding pathway downstream could be constructed properly in the engineering microbes, the biosensing could come into reality.

Compared to Lepidoptera, current application of sex pheromones for Homoptera such as aphids is less common. Mixture of nepetalactone and nepetalactol with specific ratio are shown to be sex pheromones of tea aphids and signals that attract Chrysopa pallens, which is natural enemy to tea aphids. We found that compared to chemical synthesis, biosynthesis of sex pheromones with engineering microbes is a cheaper and more renewable option, and is our solution to eco-friendliness.

Saccharomyces cerevisiae is selected for the engineering microbe. A pathway for sex pheromone production is installed in yeast as the biosynthesis part. Gene of a type of GPCR which could specifically detect benzaldehyde from air is built into the yeast cell and connected to one of its original GPCR pathways so that the detection part is complete. Linking these two parts by setting the sex pheromone production as the downstream pathway when the GPCR is activated, we got an automated tea aphid controlling biological device —— TeaFender, which represents "The Defender of Tea". By designing TeaFender we aim to provide innovative and more eco-friendly ways and trials in pest control, and to explore the vast possibilities that pest control by sex pheromone could have.

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