Actin depolymerization by Latrunculin B can either suppress or promote root gravitropism, depending on the developmental stages in Arabidopsis

Root gravitropism enables plants to optimize water and nutrient uptake, with actin filaments playing a key regulatory role. However, the effects of F-actin depolymerization on gravitropism have been inconsistent. Here, we show that actin depolymerization impacts root gravitropism in a developmentally dependent manner. In newly germinated roots, weak statolith constraint by actin means depolymerization does not significantly enhance statolith sedimentation but inhibits cell elongation on the upper root side, reducing gravitropic bending. In mature roots, stronger statolith constraint allows actin depolymerization to promote statolith sedimentation and inhibit cell elongation on the lower side, thus accelerating root bending. These findings provide new perspectives for a deeper understanding of the mechanisms underlying root gravitropism.