Elevating summer-autumn tea's utilization value: The role of endophyte CsE7 in enhancing growth and quality

As a significant economic crop in China, the flavor quality of tea plays a crucial role in determining its economic value and serves as a key factor in the competitive advantage of the high-quality development of the tea industry. Tea plants inoculated with the endophyte Luteibacter sp. CsE7 can significantly improve their nitrogen fixation, flavor and quality of tea products, leading to increased utilization efficiency and economic value of summer-autumn tea products. This study examined the effects of endophyte CsE7 on the total nitrogen content, growth status, and quality-related compounds of tea plants. The nitrogen fixation and plant-growth-promoting (PGP) activities of CsE7 were assessed to determine its effectiveness as a bacterium that supports nitrogen fixation and enhances plant growth. Through genomic and transcriptomic analyses of CsE7, two key nitrogenase proteins, CsENifB1 and CsENifB2, were identified as primary contributors to its nitrogen-fixation capability. The investigation of PGP traits revealed that CsE7 enhances plant growth by producing phytohormones, aiding siderophore biosynthesis, and synthesizing 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Based on the evaluation results of tea shoots treated with CsE7 through irrigation inoculation, it was observed that CsE7 significantly increased the weight of hundred-bud samples, and enhanced axillary bud development, and stem elongation. Inoculation with CsE7 enhanced free amino acids and theanine levels in tea shoots, enriching the taste profile while maintaining the polyphenol-to-amino acid ratio. In conclusion, Luteibacter sp. CsE7 demonstrated notable nitrogen fixation and growth-promoting capabilities, thereby enhancing the quality of tea shoots. These findings highlight its potential significance for the summer-autumn tea industry and offer a novel perspective for enhancing tea flavor quality.