The rich flavours of a quality tea are primarily influenced by the varieties of tea leaves used in its preparation. However, research published in the journal *Current Biology* on February 15th reveals that an often-overlooked component plays a critical role in crafting a delicious tea: the microbial communities present on the roots of tea plants. The study demonstrates that modifying these microbial assemblages can substantially enhance the quality of the tea.

Tongda Xu from Fujian Agriculture and Forestry University in Fujian, China, explains that microbiome studies found significant differences in the microbial communities of tea plant roots, particularly those microbes involved in nitrogen metabolism. These findings are pivotal, as the team constructed a synthetic microbial community from the roots of high-quality tea plants, which significantly increased the amino acid content across various tea plant varieties, thereby improving the tea quality.

China is renowned for its vast genetic resources for tea cultivation. However, the researchers note that enhancing tea quality through traditional molecular genetic breeding is challenging. Consequently, there is keen interest in exploring alternative methods, such as employing microbial agents, to improve and modify tea quality. Previous studies have shown that soil microbes, which reside in plant roots, play a significant role in nutrient uptake and utilisation within the plants. In this new study, the researchers aimed to delve deeper into how root microbes specifically influence tea quality.

The study revealed that the root microbes are crucial for the uptake of ammonia, which affects the production of theanine, a key component in determining the taste of tea. Furthermore, analysing various tea varieties and their theanine levels, the researchers identified specific microbes that could enhance nitrogen metabolism and increase theanine production.

Following this discovery, the team created a synthetic microbial community called SynCom, which closely replicated the microbial community associated with a high-theanine tea variety known as Rougui. Upon applying this SynCom to tea roots, they observed an increase in theanine levels. The microbes also enabled Arabidopsis thaliana, a model organism frequently used in plant biology, to tolerate low-nitrogen conditions better.

Wenxin Tang, a co-author of the study, expressed surprise at the synthetic microbial community’s broader applicability. Originally anticipated to improve only low-quality tea plants, SynCom was found to significantly enhance the quality of certain high-quality tea varieties as well, particularly under low-nitrogen soil conditions.

These findings suggest a promising future for tea cultivation, especially in nitrogen-deficient soils. The potential of synthetically produced microbial communities to enhance tea quality, coupled with the fact that tea plants are heavy nitrogen consumers, could reduce reliance on chemical fertilisers. This discovery not only promotes more sustainable agricultural practices but also holds the promise of enhancing the quality of the tea produced.

The implications of these findings are not limited to tea cultivation. The enhanced ammonium nitrogen uptake observed in tea varieties treated with SynCom21 was also noted in Arabidopsis thaliana, suggesting that this microbial community could be beneficial for other crops. This opens up a world of possibilities, improving characteristics such as protein content in rice and revolutionising sustainable agriculture.

The researchers are now at the forefront of agricultural science, focused on further optimising SynCom and evaluating its effectiveness in field trials. They also aim to explore how root microbes influence other secondary metabolites in tea plants, which could lead to additional breakthroughs in crop management. This study not only underscores the importance of microbial communities in agriculture but also highlights innovative ways to leverage these communities to enhance crop quality and sustainability, paving the way for a more sustainable and high-quality future in agriculture.

More information: Wei Xin et al, Root microbiota of tea plants regulate nitrogen homeostasis and theanine synthesis to influence tea quality, Current Biology. DOI: 10.1016/j.cub.2024.01.044

Journal information: Current Biology Provided by Cell Press