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 <i>Populus tomentosa</i> 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 <i>PtomiR171a-PtoGRAS50</i> regulatory axis that may control cellulose-related gene expression and influence fiber development in <i>P. tomentosa</i>. Single-nucleotide polymorphism (SNP)-based association studies implicated the role of the <i>PtomiR171a-PtoGRAS50</i> module in modulating FL. Combined with dual-luciferase reporter gene assay, real-time reverse transcription polymerase chain reaction (RT-qPCR), transcriptome and degradome analysis, <i>PtomiR171a</i> exerts a negative regulatory effect on <i>PtoGRAS50</i>, which is a key regulator of early xylem development. DNA affinity purification sequencing (DAP-seq) identified two downstream putative target genes of <i>PtoGRAS50</i>, both of which are involved in cellulose biosynthesis and metabolism. Unlike previous studies about miRNAs in <i>P. tomentosa</i>, this work narrows its scope to miR171 and elucidates the downstream regulatory module. Collectively, these findings elucidate a critical <i>PtomiR171a-PtoGRAS50</i> 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 <i>P. tomentosa</i>.