PmTCP18, a class I TCP transcription factor from Prunus mume, regulates plant height and branching when ectopically...

Prunus mume, an important ornamental and fruit tree in East Asia, has plant height and branching regulation mechanisms valuable for breeding new varieties that require less artificial shaping and are suitable for potting and high-yield cultivation. This study focused on the TCP family transcription factor PmTCP18, cloned from the leaf buds of the P. mume 'Feilve', and systematically investigated its expression patterns, biological functions, and regulatory mechanisms to elucidate its role in regulating plant height and branching. The results showed that PmTCP18 expression peaked during the bud break stage and was significantly induced by gibberellin and cytokinin. Overexpression of PmTCP18 in poplar notably increased plant height, stem diameter, and lateral branch formation. Furthermore, it promoted elongation of stem epidermal cells, widening of xylem and phloem tissues, and an increase in cambium cell layers, indicating that PmTCP18 regulates processes of cell division, differentiation, and elongation. Transcriptome analysis revealed that PmTCP18 overexpression affected multiple plant hormone signaling pathways and significantly upregulated the expression of ABC transporters and cell cycle-related genes. The transcription factor PmHB1 directly binds to the PmTCP18 promoter. And in the stem tips where the PmHB1 gene was silenced by VIGS, the expression level of the PmTCP18 was also significantly reduced, suggesting the PmHB1 positively regulates its expression. Collectively, this study provides novel insights into the role of PmTCP18 in regulating shoot length and branching and serves as a critical reference for deciphering the functional mechanisms of class I TCP genes in plant architectural development.