Gelatinous fibers develop asymmetrically for posture support of bends and coils in common bean vine

Gelatinous (G)-fibers are common in the stems of twining vines (twiners), but their role remain unclear given the lack of developmental insights. Here, we characterize the developmental anatomy of G-fiber formation in common bean stems (Phaseolus vulgaris L., Fabaceae). G-fibers in common bean exhibit cell wall organization comparable to other species, consisting of cellulose and Rhamnogalacturonan-I pectins, with possible traces of lignin. We show that G-fibers are absent in the actively circumnutating stems, thus these tensile fibers are not associated with the dynamic searching movements characteristics of twiners. Instead, we found that after a subtle bend or dramatic coil is formed, G-fibers form asymmetrically on the concave side of the stem for posture maintenance. Therefore, G-fibers do not drive movement, but provide support for existing bends, thus stabilizing the helical conformation of twiners around its host to avoid slippage. Finally, we present common bean as an emergent system to study twiners and growth form diversity given its easy cultivation, self-pollination, fast growth, and habit diversity arising from plant breeding, and the ability to induce habit shifts through simple modifications to light conditions.