CHARACTERIZATION OF THE AUXIN-INDUCIBLE SAUR-AC1 GENE FOR USE AS A MOLECULAR-GENETIC TOOL IN ARABIDOPSIS

The small auxin up RNA (SAUR) genes were originally characterized in s oybean, where they encode a set of unstable transcripts that are rapid ly induced by auxin. in this report, the isolation of a SAUR gene, des ignated SAUR-AC1, from Arabidopsis thaliana (L.) Heynh. ecotype Columb ia is described. The promoter of the SAUR-AC1 gene contains putative r egulatory motifs conserved among soybean SAUR promoters, as well as se quences implicated in the regulation of other genes in response to aux in. The transcribed region is approximately 500 bp in length and conta ins no introns. Highly conserved sequences located within the SAUR-AC1 transcript include the central portion of the coding region and a put ative mRNA instability sequence (DST) located in the 3' untranslated r egion. Accumulation of SAUR-AC1 mRNA is readily induced by natural and synthetic auxins and by the translational inhibitor cycloheximide. Mo reover, several auxin- and gravity-response mutants of Arabidopsis exh ibit decreased accumulation of the SAUR-AC1 mRNA in elongating etiolat ed seedlings. in particular, in the axr2-1 mutant the SAUR-AC1 transcr ipt accumulates to less than 5% of wild-type levels. These studies ind icate that SAUR-AC1 will be a useful probe of auxin-induced gene expre ssion in Arabidopsis and will facilitate the functional analysis of bo th transcriptional and posttranscriptional regulatory elements.