Genome-Wide Identification of the GDSL Gene Family and Functional Validation of DfDACX1 in Secondary Wall Synthesis in Dendrocalamus farinosus

GDSL esterases/lipases constitute a large and functionally versatile gene family in plants, yet their systematic characterization in bamboo—perennial woody grasses with exceptionally rapid shoot elongation—remains scarce. Here, we performed a genome-wide identification of the GDSL family in allohexaploid Dendrocalamus farinosus and characterized the function of a candidate gene in secondary wall synthesis. A total of 265 DfGDSL genes were identified and classified into nine clades; rice xylan deacetylases BS1 and DARX1 fell within Clade VIII, which harbors 75 members. Chromosomal distribution, exon–intron organization, conserved motifs, and collinearity analyses indicated that whole-genome and tandem duplications drove family expansion, with purifying selection as the predominant evolutionary force. Expression profiling across tissues and shoot developmental stages pinpointed DfGDSL58 as the sole highly expressed OsDARX1 homolog in D. farinosus, showing specific upregulation during rapid elongation (50–400 cm). Its promoter contains auxin-responsive elements, and exogenous NAA treatment significantly induced its expression, with a peak at 6 h. Heterologous overexpression of DfGDSL58 (designated DfDACX1) in tobacco increased plant height and basal diameter while reducing lignin and hemicellulose deposition, xylem width, and transcript levels of xylan synthase (NtIRX9) and lignin biosynthetic genes (NtC4H, NtCOMT, NtCAD), whereas cellulose content and cellulose synthase genes (NtCESA4, NtCESA7) remained largely unchanged. Collectively, these findings demonstrate that DfDACX1 negatively regulates secondary wall thickening and promotes longitudinal growth, likely via modulating xylan deacetylation and downstream lignin biosynthesis. This study presents the first systematic characterization of the GDSL family in D. farinosus and identifies DfDACX1 as a key modulator of the trade-off between cell wall deposition and rapid shoot elongation, offering mechanistic insights into bamboo’s extraordinary growth and a potential target for engineering plant architecture.