Nitrogen (N) and selenium (Se) are beneficial for tea growth and tea quality; however, it is unknown how the combined application of N and Se affects tea quality and N uptake and utilization in tea plants. In the present study, a hydroponic experiment with three N levels (0, 2 and 4.5 mmol/L) and three Se levels (0, 0.3 and 3 mg/L) was carried out with ‘Chuancha No.2’ as the material, and the contents of tea polyphenols, amino acids and caffeine as well as the expression levels of genes related to N uptake and utilization in tea plants were tracked. The findings reveal that the contents of tea polyphenols, AAs and caffeine in new shoots were the highest when supplied with 0.3 mg/L Se and 4.5 mmol/L N, while the contents of total N, AAs and tea polyphenols in mature leaves were the highest at the concentrations of 3 mg/L Se and 2 mmol/L N. Se supply (0.3 and 3 mg/L) induced an increase in amino acid and tea polyphenol contents in tea shoots under N deficiency conditions, whereas total N content, tea polyphenols and AAs in mature leaves and total N content in tea roots decreased significantly. When supplied with N (2 mmol/L and 4.5 mmol/L), the contents of tea polyphenols and caffeine in new shoots first increased and then decreased with the increase in Se concentration, while the total N content in mature leaves and roots increased. In leaves, CsAMT1.1, CsAMT1.2 and CsAMT3.1 had similar trends, and their expression levels were remarkably upregulated when supplied with 0.3 mg/L Se or 2 mmol/L N, respectively; the expression level of CsGS1.1 was significantly induced by N and Se, while CsGS1.2 and CsTS1 were mainly induced by N. In roots, CsAMT1.1 could play a major role in N uptake under the combined application of N and Se; CsGS1.2 expression was significantly induced compared to CsGS1.1 under the combined application of N and Se. This study explored the potential of the interaction of Se and N to promote tea quality and N uptake and utilization in tea plants.

As nutrient allocation trade-offs occur between reproductive and vegetative development in crops, optimizing their partitioning holds promise for improving agricultural productivity and quality. Herein, we characterize the phenotypic diversity of the fruitfulness trait and identify associated genes in tea plants (Camellia sinensis). Over three consecutive years, we monitored the fruitfulness of an F₁ hybrid population (n = 206) derived from crosses of ‘Emei Wenchun’ and ‘Chuanmu 217’. A marked variation was observed in the yield of individual plants, ranging from complete sterility (zero fruits) to exceptionally high fertility (1612 fruits). Using the high-resolution genetic linkage map and the fruitfulness data, we identified a stable major QTL designated as qFN5. To fine-map the underlying gene(s), artificial pollination experiments were conducted with extreme phenotype individuals (with the highest vs. lowest fruit numbers). Bulked segregant RNA sequencing (BSR-Seq) with ovules collected at two and seven days post-pollination (DPP) identified the genomic intervals that exhibit a high degree of overlap with qFN5. Analysis of expression dynamics combined with functional genomics data revealed a prominent candidate gene, CsETR2 (TGY048509), which encodes an ethylene receptor protein. When CsETR2 was overexpressed in Arabidopsis thaliana, the transgenic lines exhibited significantly decreased reproductive performance relative to the wild-type plants. Relative to the wild type, the transgenic lines exhibited a significant decline in several key traits: the number of effective panicles decreased by 72.5%, the seed setting rate dropped by 67.7%, and the silique length shortened by 38%. These findings demonstrate its role in regulating plant fruitfulness. Furthermore, yeast one-hybrid and dual-luciferase assays verified that CsMYB15 (TGY110225) directly binds to the CsETR2 promoter, thus repressing its transcription. In summary, our findings expand the understanding of genetic regulation underlying fruitfulness in tea plants and provide candidate target loci for breeding.