The phytohormone auxin is the major growth regulator governing tropic responses including gravitropism. Auxin build-up at the lower side of stimulated shoots promotes cell expansion, whereas in roots it inhibits growth, leading to upward shoot bending and downward root bending, respectively. Yet it remains an enigma how the same signal can trigger such opposite cellular responses. In this review, we discuss several recent unexpected insights into the mechanisms underlying auxin regulation of growth, challenging several existing models. We focus on the divergent mechanisms of apoplastic pH regulation in shoots and roots revisiting the classical Acid Growth Theory and discuss coordinated involvement of multiple auxin signaling pathways. From this emerges a more comprehensive, updated picture how auxin regulates growth.
Trends in Plant Science
The authors thank Alexandra Mally for editing the text. This work was supported by the Austrian Science Fund (FWF) I 3630-B25 to Jiří Friml and the DOC Fellowship of the Austrian Academy of Sciences to Lanxin Li. All figures were created with BioRender.com.
Li L, Gallei MC, Friml J. Bending to auxin: Fast acid growth for tropisms. Trends in Plant Science. 2022;27(5):440-449. doi:10.1016/j.tplants.2021.11.006
Li, L., Gallei, M. C., & Friml, J. (2022). Bending to auxin: Fast acid growth for tropisms. Trends in Plant Science. Cell Press. https://doi.org/10.1016/j.tplants.2021.11.006
Li, Lanxin, Michelle C Gallei, and Jiří Friml. “Bending to Auxin: Fast Acid Growth for Tropisms.” Trends in Plant Science. Cell Press, 2022. https://doi.org/10.1016/j.tplants.2021.11.006.
L. Li, M. C. Gallei, and J. Friml, “Bending to auxin: Fast acid growth for tropisms,” Trends in Plant Science, vol. 27, no. 5. Cell Press, pp. 440–449, 2022.
Li L, Gallei MC, Friml J. 2022. Bending to auxin: Fast acid growth for tropisms. Trends in Plant Science. 27(5), 440–449.
Li, Lanxin, et al. “Bending to Auxin: Fast Acid Growth for Tropisms.” Trends in Plant Science, vol. 27, no. 5, Cell Press, 2022, pp. 440–49, doi:10.1016/j.tplants.2021.11.006.
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