Project II. Isolation of a novel class of Arabidopsis mutants with impaired transduction of the gravity signal (Robertson and Muday).

This research effort is one of five integrated projects that in their totality comprise the NSCORT in Gravitational Biology. A mutant screen of T-DNA tagged Arabidopsis was performed that took advantage of the fact that inflorescence stems can perceive but not respond to gravity at 4°C. We have recovered 8 mutants, each of which show a normal response to gravity at room temperature, and have done genetic tests to segregate them into three different groups. The mutants are proposed to have lesions in their Gravity Persistent Signaling mechanism and, therefore, they have been called GPS mutants. The three mutant phenotypes are; a reverse response to gravity; a hyper-response to gravity; and a lack of response to gravity. Two of these are completely novel phenotypes that can only be explained as being defective in sensing or signal transduction (Wyatt et al. 2002, in press). The mutant genes are being cloned by Dr. Sarah Wyatt of Ohio University, formerly a postdoctoral fellow with the NSCORT. Additionally, characterization of these mutants continues as collaboration between the Wyatt and Muday laboratories. The cold treatment prevents polar auxin transport as well as gravity response, but does not impair perception of gravity in wild-type. Study of the effects of cold treatments and gravity stimulation on polar auxin transport in the wild-type and gps 1, 2 and 3 inflorescences is currently underway.

Project III
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