Poster: Late and Moved Abstracts

Abs # 976: HPH, a Repressor of Phototropic Responsiveness in Arabidopsis

Presenter:	Celaya, Brandon R, brc4yd@mizzou.edu
Authors	Celaya, Brandon R (A)   Campbell, Thomas J (A)   Liscum, Mannie  (A)
Affiliations:	(A): University Of Missouri

Phototropism, or the bending of a plant organ towards or away from directional light, represents a rapid and visually obvious response of plants to changes in their light environment. A number of proteins involved in the phototropic perception, transduction, and response have been identified, most via loss-of-function mutational screens. While robust, screens for loss-of-function mutations fail to identify either redundant genes or negative regulators of the process being examined. Thus, we have developed a new screen to identify physiological gain-of-function mutants to allow a broader coverage of the possible recoverable mutations. Briefly, dark-grown mutagenized seedlings are exposed to a unidirectional blue light treatment that normally fails to induce a response in wild-type seedlings and positively phototropic seedlings are selected. Using this approach we have identified three mutants that respond both more quickly and stronger than their wild-type background. The recessive nature of each of these mutations indicates that the associated gain-of-function phenotypes result from genetic loss-of-function lesions in a negative regulator. One of these mutants, hph (hyper-phototropic hypocotyl), is being characterized in detail. Physiological analyses indicate that HPH is involved specifically in phototropism as the mutant exhibits a wild-type gravitropic response. A large F₂ population has been generated from a cross of hph with a polymorphic wild-type background and hph mutants subsequently selected for mapping purposes. HPH represents the first repressor molecule identified in the phototropic signal-response pathway.