Biphasic control of cell expansion by auxin coordinates etiolated seedling development

• Published in: Science advances Vol. 8; no. 2; p. eabj1570
• Main Authors: Du, Minmin, Bou Daher, Firas, Liu, Yuanyuan, Steward, Andrew, Tillmann, Molly, Zhang, Xiaoyue, Wong, Jeh Haur, Ren, Hong, Cohen, Jerry D, Li, Chuanyou, Gray, William M
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 14-01-2022
• Subjects: Biomedicine and Life Sciences; Life Sciences; Plant Sciences; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.abj1570

Seedling emergence is critical for food security. It requires rapid hypocotyl elongation and apical hook formation, both of which are mediated by regulated cell expansion. How these events are coordinated in etiolated seedlings is unclear. Here, we show that biphasic control of cell expansion by the phytohormone auxin underlies this process. Shortly after germination, high auxin levels restrain elongation. This provides a temporal window for apical hook formation, involving a gravity-induced auxin maximum on the eventual concave side of the hook. This auxin maximum induces
expression, leading to asymmetrical H
-ATPase activity across the hypocotyl that contributes to the differential cell elongation underlying hook development. Subsequently, auxin concentrations decline acropetally and switch from restraining to promoting elongation, thereby driving hypocotyl elongation. Our findings demonstrate how differential auxin concentrations throughout the hypocotyl coordinate etiolated development, leading to successful soil emergence.