Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis

article Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis published yes Lianghanxiao Sun author Wenxin Jia author Yanbo Mao author Xin Li author Mengjuan Kong author Ji She author Jiří Friml author 4159519E-F248-11E8-B48F-1D18A9856A870000-0002-8302-7596 Shutang Tan author 2DE75584-F248-11E8-B48F-1D18A9856A870000-0002-0471-8285 JiFr department Gravitropism is a fundamental adaptive response in plants that enables directional growth to optimize resource acquisition. In this study, we employed forward genetic screening to identify Arabidopsis mutants with defective hypocotyl gravitropism and isolated the short and agravitropic hypocotyl in dark1 (sad1) mutant, which carries a point mutation (G110E) in the SAC1 gene encoding a phosphoinositide phosphatase. Deficiency of SAC1 disrupted gravity-induced polar localization of PIN3 in endodermal cells, impairing auxin redistribution and leading to hypocotyl gravitropism defects. Subcellular localization analysis revealed that SAC1 is partially localized to the PVC/tonoplast and participates in late endosomal trafficking. The sac1 mutation leads to abnormal vacuolar morphology, which is associated with defects in amyloplast sedimentation during the gravitropic response in Arabidopsis shoots. We further revealed that SAC1 interacts with GRV2, a key regulator of the late endocytic pathway, and that both proteins cooperatively regulate shoot gravitropism. In summary, this study identified SAC1 as a regulator of shoot gravitropism, revealing its important role in modulating vacuolar homeostasis, amyloplast sedimentation, PIN3 trafficking, and auxin distribution. These findings provide insights into the molecular mechanisms linking membrane transport to environmental adaptation in plants. Wiley2026 eng auxinSAC1GRV2PIN3vacuolegravitropismArabidopsis The Plant Journal 0960-7412 1365-313X 4243807510.1111/tpj.71042 1271 Sun, Lianghanxiao, et al. “Regulation of Shoot Gravitropism and Branching Angle by the GRV2-SAC1 Axis in Arabidopsis.” The Plant Journal, vol. 127, no. 1, e71042, Wiley, 2026, doi:<a href="https://doi.org/10.1111/tpj.71042">10.1111/tpj.71042</a>. Sun L, Jia W, Mao Y, et al. Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis. The Plant Journal. 2026;127(1). doi:<a href="https://doi.org/10.1111/tpj.71042">10.1111/tpj.71042</a> Sun, L., Jia, W., Mao, Y., Li, X., Kong, M., She, J., … Tan, S. (2026). Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis. The Plant Journal. Wiley. <a href="https://doi.org/10.1111/tpj.71042">https://doi.org/10.1111/tpj.71042</a> L. Sun, W. Jia, Y. Mao, X. Li, M. Kong, J. She, J. Friml, S. Tan, The Plant Journal 127 (2026). Sun L, Jia W, Mao Y, Li X, Kong M, She J, Friml J, Tan S. 2026. Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis. The Plant Journal. 127(1), e71042. Sun, Lianghanxiao, Wenxin Jia, Yanbo Mao, Xin Li, Mengjuan Kong, Ji She, Jiří Friml, and Shutang Tan. “Regulation of Shoot Gravitropism and Branching Angle by the GRV2-SAC1 Axis in Arabidopsis.” The Plant Journal. Wiley, 2026. <a href="https://doi.org/10.1111/tpj.71042">https://doi.org/10.1111/tpj.71042</a>. L. Sun et al., “Regulation of shoot gravitropism and branching angle by the GRV2-SAC1 axis in Arabidopsis,” The Plant Journal, vol. 127, no. 1. Wiley, 2026. 223662026-07-19T22:01:47Z2026-07-20T13:53:44Z