Integration of light and abscisic acid signaling during seed germination and early seedling development

doi:10.1073/pnas.0710778105

Integration of light and abscisic acid signaling during seed germination and early seedling development

*Donald Danforth Plant Science Center, St Louis, MO 63132;
^†Department of Biology, Washington University, St. Louis, MO 63130;
^‡Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164;
^§Department of Applied Plant Science, Chonnam National University, Gwangju 500-757, South Korea; and
^¶Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520

Edited by Maarten Koornneef, Wageningen University and Research Centre, Wageningen, The Netherlands, and approved January 31, 2008 (received for review November 13, 2007)

Abstract

Seed germination is regulated by endogenous hormonal cues and external environmental stimuli such as water, low temperature, and light. After germination, the young seedling must rapidly establish its root system and the photoautotrophic capability appropriate to its surrounding environment. Light and the phytohormone abscisic acid (ABA) both regulate seed germination and seedling development, although how light and ABA signals are integrated at the molecular level is not understood. Here, we found that the previously described light-signaling component HY5 also mediates ABA response in seed germination, early seedling growth, and root development in Arabidopsis. HY5 binds to the promoter of the transcription factor ABI5 gene with high affinity and is required for the expression of ABI5 and ABI5-targeted late embryogenesis-abundant genes in seeds. Chromatin immunoprecipitation also indicated that the binding of HY5 to the ABI5 promoter is significantly enhanced by ABA. Overexpression of ABI5 restores ABA sensitivity in hy5 and results in enhanced light responses and shorter hypocotyls in the wild type. Our studies identified an unexpected mode of light and ABA signal integration that may help young seedlings better adapt to environmental stresses.

Footnotes

^‖To whom correspondence should be addressed. E-mail: lxiong{at}danforthcenter.org
Author contributions: H.C., M.M.N., and L.X. designed research; H.C., J.Z., and S.-W.H. performed research; H.Z. and X.-W.D. contributed new reagents/analytic tools; H.C., J.Z., M.M.N., and L.X. analyzed data; and H.C. and L.X. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0710778105/DC1.