The AtPIN2 gene in Arabidopsis thaliana is involved in root gravitropism control. Researchers identified a null mutant, Atpin2::En701, through transposon mutagenesis, which exhibited agravitropic root growth and altered auxin sensitivity, similar to the wav6-52 mutant. The AtPIN2 gene was mapped to chromosome 5 and found to be allelic to wav6-52. The gene encodes a 69 kDa protein with 10 putative transmembrane domains, similar to the major facilitator superfamily of transport proteins. The protein is polarly localized in root cells, suggesting a role in polar auxin transport. Expression analysis showed AtPIN2 is expressed in root tips and localized in cortical and epidermal cell membranes. The Atpin2::En701 mutant showed increased sensitivity to auxins like 1-NAA and IAA, consistent with a defect in auxin efflux. The AtPIN2 protein is likely a transmembrane component of the auxin efflux carrier complex, playing a key role in root gravitropism by regulating auxin redistribution. The study supports the Cholodny-Went hypothesis, showing that auxin transport is essential for gravitropic responses. The findings highlight the importance of AtPIN2 in controlling root gravitropism through polar auxin transport.The AtPIN2 gene in Arabidopsis thaliana is involved in root gravitropism control. Researchers identified a null mutant, Atpin2::En701, through transposon mutagenesis, which exhibited agravitropic root growth and altered auxin sensitivity, similar to the wav6-52 mutant. The AtPIN2 gene was mapped to chromosome 5 and found to be allelic to wav6-52. The gene encodes a 69 kDa protein with 10 putative transmembrane domains, similar to the major facilitator superfamily of transport proteins. The protein is polarly localized in root cells, suggesting a role in polar auxin transport. Expression analysis showed AtPIN2 is expressed in root tips and localized in cortical and epidermal cell membranes. The Atpin2::En701 mutant showed increased sensitivity to auxins like 1-NAA and IAA, consistent with a defect in auxin efflux. The AtPIN2 protein is likely a transmembrane component of the auxin efflux carrier complex, playing a key role in root gravitropism by regulating auxin redistribution. The study supports the Cholodny-Went hypothesis, showing that auxin transport is essential for gravitropic responses. The findings highlight the importance of AtPIN2 in controlling root gravitropism through polar auxin transport.