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DEVELOPMENT AND HORMONE ACTION

The F-Box Protein MAX2 Functions as a Positive Regulator of Photomorphogenesis in Arabidopsis^{1,[C],[W],[OA]}

Section of Molecular Cell and Developmental Biology and Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712

Light is vital for plant growth and development. To respond to ambient light signals, plants are equipped with an array of photoreceptors, including phytochromes that sense red (R)/far-R (FR) regions and cryptochromes and phototropins that respond to the ultraviolet-A/blue (B) region of the light spectrum, respectively. Several positively and negatively acting components in light-signaling pathways have been identified using genetic approaches; however, the pathways are not saturated. Here, we characterize a new mutant named pleiotropic photosignaling (pps), isolated from a genetic screen under continuous R light. pps has longer hypocotyls and slightly smaller cotyledons under continuous R, FR, and B light compared to that of the wild type. pps is also hyposensitive to both R and FR light-induced seed germination. Although photosynthetic marker genes are constitutively expressed in pps in the dark at high levels, the expression of early light-regulated genes is reduced in the pps seedlings compared to wild-type seedlings under R light. PPS encodes MAX2/ORE9 (for MORE AXILLARY BRANCHES2/ORESARA9), an F-box protein involved in inflorescence architecture and senescence. MAX2 is expressed ubiquitously in the seedling stage. However, its expression is restricted to vascular tissues and meristems at adult stages. MAX2 is also localized to the nucleus. As an F-box protein, MAX2 is predicted to be a component of the SCF (for SKP, Cullin, and F-box protein) complex involved in regulated proteolysis. These results suggest that SCF^MAX2 plays critical roles in R, FR, and B light-signaling pathways. In addition, MAX2 might regulate multiple targets at different developmental stages to optimize plant growth and development.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Enamul Huq (huq{at}mail.utexas.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.107227

^* Corresponding author; e-mail huq{at}mail.utexas.edu.

Received August 10, 2007; accepted October 8, 2007; published October 19, 2007.

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