Background: miRNAs are a type of conserved, small RNA molecule that regulate gene expression and play an important role in the growth and development of plants. miRNAs are involved in seed germination, root development, shoot apical meristem maintenance, leaf development, and flower development by regulating various target genes. However, the role of miRNAs in the mechanism of tea plant flower sterility remains unclear. Therefore, we performed miRNA sequencing on the flowers of fertile male parents, female parents, and sterile offspring. Results: A total of 55 known miRNAs and 90 unknown miRNAs were identified. In the infertile progeny, 37 miRNAs were differentially expressed; 18 were up-regulated and 19 were down-regulated. miR156, miR157, miR164, miR167, miR169, miR2111 and miR396 family members were down-regulated, and miR160, miR172 and miR319 family members were up-regulated. Moreover, we predicted that the 37 differentially expressed miRNAs target a total of 363 genes, which were enriched in 31 biological functions. We predicted that miR156 targets 142 genes, including ATD1A, SPL, ACA1, ACA2, CKB22 and MADS2. Conclusion: We detected a large number of differentially expressed miRNAs in the sterile tea plant flowers, and their target genes were involved in complex biological processes. Among these miRNAs, the down-regulation of miR156 may be one of the factor in the formation of sterile floral buds in tea plants.

Background: The growth process of the tea plant (Camellia sinensis) includes vegetative growth and reproductive growth. The reproductive growth period is relatively long (approximately 1.5 years), during which a large number of nutrients are consumed, resulting in reduced tea yield and quality, accelerated aging, and shortened economic life of the tea plant. The formation of unisexual and sterile flowers can weaken the reproductive growth process of the tea plant. To further clarify the molecular mechanisms of pistil deletion in the tea plant, we investigated the transcriptome profiles in the pistil-deficient tea plant (CRQS), wild tea plant (WT), and cultivated tea plant (CT) by using RNA-Seq. Results: A total of 3683 differentially expressed genes were observed between CRQS and WT flower buds, with 2064 upregulated and 1619 downregulated in the CRQS flower buds. These genes were mainly involved in the regulation of molecular function and biological processes. Ethylene synthesis–related ACC synthase genes were significantly upregulated and ACC oxidase genes were significantly downregulated. Further analysis revealed that one of the WIP transcription factors involved in ethylene synthesis was significantly upregulated. Moreover, AP1 and STK, genes related to flower development, were significantly upregulated and downregulated, respectively. Conclusions: The transcriptome analysis indicated that the formation of flower buds with pistil deletion is a complex biological process. Our study identified ethylene synthesis, transcription factor WIP, and A and D-class genes, which warrant further investigation to understand the cause of pistil deletion in flower bud formation.

As an important economic crop, the development of floral organs in tea plants plays an essential role in tea yield, quality, and varietal improvement. Previous studies have shown significant downregulation of the CsSTK gene in the pistil-deficient mutant ‘Yuncha Qirui’ (CRQS) during flower development, suggesting its involvement in floral organ and pistil development. This study investigated CsSTK function and regulatory mechanisms, concurrently conducting a systematic identification of the BPC transcription factor family members in tea plants. The results showed that CsSTK is specifically expressed in tea plant flowers (particularly in pistils) and fruit tissues. Notably, its expression level in CRQS flower buds was less than 1% of that in normal tea plants, whereas it was significantly upregulated in the sterile-flower mutant ‘Yuncha Yirui’ (ZDH), which exhibits abnormal fused carpels. Heterologous overexpression of CsSTK was found to promote early flowering in Arabidopsis, indicating its involvement in flowering time regulation. Additionally, genome-wide analysis identified 12 BPC family members in tea plants, which were divided into three subclasses (Class Ⅰ, Ⅱ, and Ⅲ). Except for CsBPC6.4, all other CsBPCs showed higher expression levels in normal flower buds compared to fully bloomed flowers, consistent with the CsSTK expression pattern. Further studies demonstrated that CsBPC5 positively regulates CsSTK expression. This study elucidates the key regulatory role of CsSTK in tea plant floral organ development and explores the molecular mechanism underlying the CsBPC5-CsSTK regulatory module. These findings provide important theoretical insights into the molecular basis of floral organ development in tea plants.