Poster: Signaling, cell-to-cell

Abs # 429: Expression and functional characterization of Arac7

Presenter:	Nibau, Candida , cnibau@nsm.umass.edu
Authors	Nibau, Candida  (A)   Tao, Lizhen  (B)   Wu, Henming  (B)   Cheung, Alice  (A) (B)
Affiliations:	(A): Plant Biology Graduate Program-University of Massachusetts- Amherst (B): Department of Biochem & Mol. Biology- University of Massachusetts- Amherst

Plant hormones are important factors regulating growth and development. Acting coordinately, they create an intricate network of signaling cues that must be correctly perceived by the plant in order to generate a specific response. How these signals are sensed and integrated is not yet clear. Rac-like small GTPases (Racs) are emerging as important components of these signaling pathways. Here we show that an Arabidopsis type II Rac, Arac7, plays an important role in a subset of hormone signaling pathways. We show that Arac7 is expressed in actively dividing areas in Arabidopsis seedlings, while in mature plants the expression is mainly observed in meristems and throughout lateral root development. Auxin stimulates transcription from the Arac7 promoter while ABA represses it. Membrane bound Arac7 acts as a negative regulator of auxin signaling while having a positive effect in ABA-related processes. Overexpression of Arac7 seems not to have a direct effect in other hormone signaling pathways tested. Because ABA and auxin classically have opposing roles in growth and development, we propose that Arac7 acts as an integration point of these two pathways. Moreover, the fact that Arac7 expression is influenced by auxin and ABA provides a mechanism that may coordinate the two signaling pathways.