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Identification and Characterization of ARF9 as a GPS3-like Mutant.  D.R. Roberts¹, and S.E. Wyatt^{1 1}Dept. of Environmental & Plant Biology, Ohio Univ., Athens, OH.

   The gravity persistent signal gps3 mutant of Arabidopsis thaliana displays an unusual phenotype when gravistimulated at 4ºC and returned to room temperature.  This GPS3 gene encodes a transcription factor that belongs to the Auxin Response Factor (ARF) gene family (member ARF23) and contains a B3 DNA binding domain.  Using a bioinformatics approach, five other genes have been identified that are similar to GPS3.  ARF9 (one of five) is most closely related to GPS3 , though the GPS3 gene contains only the B3 DNA binding domain; ARF9 contains an Auxin Response domain and an Auxin IAA binding domain in addition to the B3 DNA binding domain. Three SALK T-DNA insertion lines were obtained for ARF9 to perform a phenotypic characterization which consisted of measuring growth rates, phenotype and gravistimulation.  Plants homozygous for the SALK T-DNA insertion were gravistimulated at 4ºC, one of the ARF9 insertion lines displayed a phenotype identical to that of the gps3 mutant.  The SALK T-DNA insertion line showed no abnormal phenotype during development.  Implying that GPS3 and ARF9 have similar function, though the structure of the genes differ.  The molecular characterization and complementation of the ARF9 gene has the potential to create a better understanding of the pathways being followed during gravity stimulus. 

(Partially Supported by Grasselli-Brown Undergraduate Research Award, Ohio University, to DRR and NASA: NAG2-1608 to SEW.)