Geraniol is an important contributor to the pleasant floral scent of tea products and one of the most abundant aroma compounds in tea plants; however, its biosynthesis and physiological function in response to stress in tea plants remain unclear. Here, we studied eight terpene synthases with expression levels that were correlated with geraniol accumulation in different tissues of tea plants. The proteins encoded by the full-length terpene synthase ( CsTPS1) and its alternative splicing isoform ( CsTPS1- AS) could catalyze the formation of geraniol when GPP was used as a substrate in vitro, whereas the expression of CsTPS1- AS was only significantly induced by Colletotrichum gloeosporioides and Neopestalotiopsis sp. infection. Silencing of CsTPS1 and CsTPS1- AS resulted in a significant decrease in the geraniol content in tea plants. The geraniol content and antifungal activity of tea plants were compared when CsTPS1 and CsTPS1- AS were silenced. Down-regulation of the expression of CsTPS1- AS reduced the accumulation of geraniol, and the silenced tea plants exhibited greater susceptibility to pathogen infection than control plants. However, the geraniol content and pathogen resistance of CsTPS1-silenced plants and control plants did not significantly differ. Further analysis showed that silencing of CsTPS1- AS led to a decrease in the expression of the defense-related genes PR1 and PR2 and the expression of SA pathway-related genes in tea plants, which increased the susceptibility of tea plants to pathogenic fungal infections . Both in vitro and in vivo results indicated that CsTPS1 is involved in the regulation of geraniol formation and plant defense via alternative splicing in tea plants. The results of this study provide new insights into geraniol biosynthesis and highlight the role of monoterpene synthases in modulating plant disease resistance via alternative splicing.

Tea is the second most consumed non-alcoholic beverage, only next to water. However, its production and qualities, including rich flavors and numerous health benefits, are often degraded by environmental stresses and contaminations with various agrochemicals. While most of tea quility-contributing secondary metabolites are synthesized in tea plant leaves, such as catechins, caffeine, volatiles, saponins, and theanine, primarily for defenses against biotic and abiotic stresses, few tea garden management measures have employed this tea plant innate innumity to enhance their tolerance against environmental stresses. This is partly due to the limited understanding of the biosynthesis and regulationof tea plant secondary metabolism. Given the importance of tea plant secondary metabolites for both tea flavors, health functions, and resistance against environmental stresses, study and in-depth understanding of the biosynthesis and environmental regulation of tea plant specialized metabolites are highly expected. Strategies developed from these studies would promote the production of safe and high quality teas. The review highlights relevant contexts of tea plant-environmental interaction at the secondary metabolism interfaces, particular their roles in enhancement of tea plant innate immunity and tea quality, so as to guide future research on genetic improvement of tea plants for safer food production and better human nutrition.

Tea is the second most consumed non-alcoholic beverage, only next to water. However, its production and qualities, including rich flavors and numerous health benefits, are often degraded by environmental stresses and contaminations with various agrochemicals. While most of tea quility-contributing secondary metabolites are synthesized in tea plant leaves, such as catechins, caffeine, volatiles, saponins, and theanine, primarily for defenses against biotic and abiotic stresses, few tea garden management measures have employed this tea plant innate innumity to enhance their tolerance against environmental stresses. This is partly due to the limited understanding of the biosynthesis and regulationof tea plant secondary metabolism. Given the importance of tea plant secondary metabolites for both tea flavors, health functions, and resistance against environmental stresses, study and in-depth understanding of the biosynthesis and environmental regulation of tea plant specialized metabolites are highly expected. Strategies developed from these studies would promote the production of safe and high quality teas. The review highlights relevant contexts of tea plant-environmental interaction at the secondary metabolism interfaces, particular their roles in enhancement of tea plant innate immunity and tea quality, so as to guide future research on genetic improvement of tea plants for safer food production and better human nutrition.

While most people know the rich flavors, pleasant tastes, and numerous health benefits of teas, various contaminations with chemicals for controling weeds, insects, microbial pathogens and other tea garden managements, become increasingly concerned on tea products. Meanwhile most of tea secondary metabolites concentrated in tea leaves, such as catechins, affeine, volatiles, saponins, and theanine, are synthesized primarily for defenses against both biotic and abiotic stresses. However, few use of these plant natural products for weed, pest and disease control by tea producers disabled the sustainable and safty production of teas. This is partly because the lacking of detailed information about biosynthesis, regulation, defense mechanism of these tea specialized metabolites due to chemical diversity and metabolic complexicity. An in-depth understanding of the biosynthesis, regulation, and defensive mechanisms of these specialized metabolites would greatly facilitate the employment of the innate immunity of tea plants to minimaize the use of other health-harmful chemicals. The review highlights relevant contexts of metabolic genomics of tea plants, so as to guaide future research on genetic improvement of tea plants for both safety and nutritional quality of teas.