Identification of miR171a-GRAS50 Regulatory Module Associated with Wood Properties in Populus tomentosa

Enhancing wood properties, particularly fiber length (FL), represents a critical objective in Populus tomentosa breeding programs. However, the molecular mechanisms regulating these traits remain largely elusive. Here, an integrative analysis of the PtomiR171 family, uncovering substantial functional divergence among PtomiR171 family members and identified a PtomiR171a-PtoGRAS50 regulatory axis that may control cellulose-related gene expression and influence fiber development in P. tomentosa. Single-nucleotide polymorphism (SNP)-based association studies implicated the role of the PtomiR171a-PtoGRAS50 module in modulating FL. Combined with dual-luciferase reporter gene assay, real-time reverse transcription polymerase chain reaction (RT-qPCR), transcriptome and degradome analysis, PtomiR171a exerts a negative regulatory effect on PtoGRAS50, which is a key regulator of early xylem development. DNA affinity purification sequencing (DAP-seq) identified two downstream putative target genes of PtoGRAS50, both of which are involved in cellulose biosynthesis and metabolism. Unlike previous studies about miRNAs in P. tomentosa, this work narrows its scope to miR171 and elucidates the downstream regulatory module. Collectively, these findings elucidate a critical PtomiR171a-PtoGRAS50 regulatory axis, advancing our understanding of the genetic networks that orchestrate wood properties, deepening insights into FL modulation, and laying a foundation for the development of targeted genetic strategies to enhance wood quality in P. tomentosa.