Altered Metabolite Profiling and Gene Expression During Adventitious Root Regeneration From Tea Stem Cuttings:...

As the most widely used tea propagation method, the whole process of root initiation and plantlet formation from tea stem cuttings is still not fully understood regarding its effects on tea plant stress, metabolism, and nutritional value. Through transcriptome analysis and targeted metabolite profiling of adventitious roots (AR) at different stages of regeneration and growth derived from tea stem nodal cuttings, we showed that flavonol content increased from low levels during the AR initiation (R1) and appearance (R2) stages to the elongation (R3) and expansion (R4) stages. In contrast, catechins content decreased during these stages. Theanine content increased from low levels at AR initiation stage R1 to higher levels at AR appearance and growth stages R2 and R3, and slightly decreased at the expansion stage R4. Caffeine content continuously decreased as AR grew, reaching its lowest at stages R3 and R4. The expression patterns of key metabolic genes (CsANS1, CsANR1, CsLAR1, CsFLS4, CsTCS4, CsTSI, CsAlaDC, CsAAT3) associated with these pathways were consistent with the observed metabolite profiles. The regulator genes related to AR development and growth or hormone signaling were also analyzed with regards to their roles in the regulation of AR growth and development and secondary metabolism during plantlet establishment. This study provides fresh insights into targeted metabolite changes and metabolic pathways during AR emergence, appearance, growth, and expansion, leading to the establishment of plantlets derived from stem cuttings. These findings lay a foundation for better understanding of tea AR architecture formation, nutrient acquisition capacity, connecting with the stem tip growth, and tea-specific secondary metabolism and nutritional composition in tea plants.