MicroRNA257 promotes secondary growth in hybrid poplar

Populus, a significant fast-growing tree species with global afforestation and energy potential, holds considerable economic value. The abundant production of secondary xylem by trees, which serves as a vital resource for industrial purposes and human sustenance, necessitates the orchestration of various regulatory mechanisms, encompassing transcriptional regulators and microRNAs (miRNAs). Nevertheless, the investigation of microRNA-mediated regulation of poplar secondary growth remains limited. In this study, we successfully isolated a novel microRNA (Pag-miR257) from 84 K poplar and subsequently integrated it into the 35 S overexpression vector. The overexpression of Pag-miR257 resulted in notable increases in plant height, stem diameter, and fresh weight. Additionally, the overexpression of Pag-miR257 demonstrated a significant enhancement in net photosynthetic rate. The findings from the examination of cell wall autofluorescence indicated a substantial increase in both xylem area and the number of vessels in poplar plants overexpressing Pag-miR257. Furthermore, the cell wall of the Pag-miR257 overexpressing plants exhibited thickening as observed through transmission electron microscopy. Moreover, the Fourier Transforms Infrared (FTIR) analysis and phloroglucinol-HCl staining revealed an elevation in lignin content in Pag-miR257 overexpressing poplar plants. The findings of this study suggest that microRNA257 may play a role in the control of secondary growth in poplar stems, thereby potentially enhancing the development of wood engineering techniques for improved material and energy production.