Poster: Late and Moved Abstracts

Abs # 996: Using global expression analysis to find putative ARF7 targets

Presenter:	Esmon, Cairn Alex, cae8r3@mizzou.edu
Authors	Esmon, Cairn Alex (A)   Ljung, Karin  (B)   Sandberg, Goran  (B)   Liscum, Mannie  (A)
Affiliations:	(A): University of Missouri-Columbia (B): Swedish University of Agricultural Sciences

The finding that NPH4/ARF7,an auxin response factor, is involved in the establishment of phototropic and gravitropic curvature, gives credence to the long held notion that a tropic curve requires the formation and response to localized changes in auxin concentration. Moreover, the association of NPH4/ARF7 with tropic responses indicates that auxin-dependent changes in gene expression are essential to these responses. In an attempt to identify "tropic stimulation-responsive genes" we isolated tissue from Brassica oleracea seedlings that had been stimulated either phototropically or gravitropically at two different time points in the responses. In particular, we isolated RNA from "lit" and "shaded" flanks of unilaterally irradiated Brassica seedlings, and "top" and the "bottom" flanks of seedlings whose growth axis was re-oriented 90„a to stimulate a gravitropic response. We have used these RNAs to probe Arabidopsis Affymetrix whole genome array chips in order to monitor global changes in gene expression between the two sides when compared to an un-stimulated control. We have also measured free auxin contents in hypocotyl tissues isolated from Brassica seedlings to determine whether or not an auxin gradient exists across a tropically-responsive hypocotyl. The results of this experiment show there is an auxin gradient formed across an elongating hypocotyl on the order of that previously measured in maize coleoptiles. These findings lead us to hypothesize that it is perhaps a combination of transcriptional activation (which is likely auxin-dependent) and repression (which is likely auxin-independent) in opposing sides of the seedlings that is leading to the tropic curve.