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EFFECTS OF SIMULATED MICROGRAVITY AND HYPERGRAVITY ON THE EXPRESSION OF ARABIDOPSIS GENES ENCODING CALMODULINS AND CALMODULIN-BINDING PROTEINS.  B.W. Poovaiah¹, T. Yang¹ and J.J.W.A. van Loon². ¹Department of Horticulture, Washington State University, Pullman, WA. ²DESC, OCB-ACTA-VU, Amsterdam, Netherlands.

     Calcium and calmodulin (CaM) play an important role in plant gravity signal transduction. However, the molecular and biochemical mechanisms involved are not clearly understood. To study the effects of gravity-induced changes on the expression of genes involved in Ca²⁺/CaM-mediated signaling, two week old Arabidopsis seedlings were subjected to simulated microgravity using the Random Positioning Machine, and hypergravity (10 g) using the MidiCAR centrifuge (ranging from 5 hrs to 5 days). The changes in mRNA levels of 11 CaM /CaM-like genes, and 20 genes encoding CaM-binding proteins were studied by RT-PCR using gene-specific primers. Actin 8 was used as a positive internal control. Selective and significant differences were observed between controls and simulated microgravity and hypergravity treated samples.  Three CaM genes were induced by simulated microgravity and one was induced by both hypergravity and simulated microgravity. Similarly, we have identified several genes encoding CaM-binding proteins that are differentially expressed in response to gravi-stimulation. Our results suggest that these genes may play an important role in gravity signal transduction. 

     (Supported by NASA grant NAG5-4841 to Poovaiah and SRON / NIVR combined grant # MG-051 to van Loon)