The study investigates the molecular mechanisms underlying gravity perception and signal transduction in plants, focusing on the role of the AtPIN2 gene in root gravitropism. The authors isolated an Arabidopsis mutant, Atpin2::En701, which exhibits agravitropic root growth and altered auxin sensitivity. Genetic mapping and analysis revealed that the Atpin2::En701 mutant is allelic to the wavy-52 mutant, both of which map to chromosome 5. The AtPIN2 gene encodes a protein with a predicted molecular mass of 69 kDa, containing 10 putative transmembrane domains and a central hydrophilic loop, similar to members of the major facilitator superfamily of transport proteins. Northern blot and Western blot analyses confirmed the expression of AtPIN2 in root tips, and immunostaining revealed a polar localization of AtPIN2 in root cortical and epidermal cells. The Atpin2::En701 mutant showed reduced root elongation and increased sensitivity to auxins, consistent with a defect in auxin efflux. These findings suggest that AtPIN2 plays a crucial role in regulating gravitropism by controlling the redistribution of auxin from the stele to the elongation zone of roots.The study investigates the molecular mechanisms underlying gravity perception and signal transduction in plants, focusing on the role of the AtPIN2 gene in root gravitropism. The authors isolated an Arabidopsis mutant, Atpin2::En701, which exhibits agravitropic root growth and altered auxin sensitivity. Genetic mapping and analysis revealed that the Atpin2::En701 mutant is allelic to the wavy-52 mutant, both of which map to chromosome 5. The AtPIN2 gene encodes a protein with a predicted molecular mass of 69 kDa, containing 10 putative transmembrane domains and a central hydrophilic loop, similar to members of the major facilitator superfamily of transport proteins. Northern blot and Western blot analyses confirmed the expression of AtPIN2 in root tips, and immunostaining revealed a polar localization of AtPIN2 in root cortical and epidermal cells. The Atpin2::En701 mutant showed reduced root elongation and increased sensitivity to auxins, consistent with a defect in auxin efflux. These findings suggest that AtPIN2 plays a crucial role in regulating gravitropism by controlling the redistribution of auxin from the stele to the elongation zone of roots.