Brassinosteroid treatment reveals the importance of xyloglucan transglucosylase/hydrolase (XTH) genes in growth habit determination of twining common bean vines

O_LIBrassinosteroids impact the development of G-fibers --specialized cells that generate tension in plants. To explore the functional and genetic relationships between G-fibers and twining stems of common bean, we applied an active brassinosteroid and a brassinosteroid inhibitor to perturb G-fiber development and probed these phenotypes through gene expression and anatomical analyses. C_LIO_LIBrassinosteroid treatment generated phenotypes that aKected the three key features of twining: elongation, circumnutation, and G-fiber development. We examined anatomical and biochemical changes in the G-fibers through cross-sections, macerations, and immunohistochemistry. RNA sequencing and differential gene expression analysis allowed us to identify unique gene expression patterns for each treatment. C_LIO_LIBrassinosteroid treatment led to significantly elongated internodes with disrupted circumnutation and long, thin-walled G-fibers. In contrast, inhibitor treatment produced short internodes with thick G-fibers. These phenotypes corresponded with significant differential expression of XTH genes, both at the onset of elongation and later, during G-layer deposition. Detection of xyloglucan epitopes in the G-layer, along with in situ hybridization, confirmed active xyloglucan remodeling after twining. C_LIO_LIOur results confirm the presence of xyloglucan in the G-layer of common bean, underscoring its importance in G-fiber function, and suggests a regulatory role for XTH genes in shaping the twining growth habit through modulation of cell wall properties. C_LI