The gmall auxin I I P !NA (SAUR) genes were originally characterized in soybean, where they encode a set of unstable transcripts that are rapidly induced by auxin. In this report, the isolation of a

No abstract

The small‐auxin‐up‐RNA (SAUR) transcripts are rapidly induced by auxin and are among the most short‐lived mRNAs in higher plants. In this study, we investigate the regulation of SAUR‐AC1, a well characterized SAUR gene of Arabidopsis. Be examining the expression of chimeric genes in transgenic tobacco, we demonstrate that the promoter region of SAUR‐AC1 mediates auxin induction. Sequences downstream of the promoter region were found to limit mRNA accumulation in a manner that was independent of auxin treatment. Both the coding region and the 3′ untranslated region (UTR) of SAUR‐AC1 independently contribute to this limitation. Effects on mRNA stability were assayed using chimeric genes under the control of the tetracycline‐repressible Top10 promoter. mRNA half‐life analysis following tetracycline treatment showed that the SAUR‐AC1 coding region does not contain elements that decrease mRNA stability. In contrast, the 3′ UTR was found to act as a potent mRNA instability determinant. This finding and the general utility of the Top10 system should provide the means to elucidate mRNA decay pathways that are potentially novel and specific for certain unstable transcripts.

The labile SAUR transcripts from higher plants contain a conserved DST sequence in their 3'-untranslated regions. Two copies of a DST sequence from soybean are sufficient to destabilize reporter transcripts in cultured tobacco cells whereas variants bearing mutations in the conserved ATAGAT or GTA regions are inactive. To investigate the potential for conserved recognition components in mammalian and plant cells, we examined the function of this instability determinant in mouse NIH3T3 fibroblasts and tobacco BY2 cells. In fibroblasts, a tetrameric DST element from soybean accelerated deadenylation and decay of a reporter transcript. However, a version mutated in the ATAGAT region was equally effective in this regard, and a tetrameric DST element from Arabidopsis was inactive. In contrast, the soybean DST element was more active as an mRNA instability element than the mutant version and the Arabidopsis element, when tested as tetramers in tobacco cells. Hence, the plant DST element is not recognized in animal cells with the same sequence requirements as in plant cells. Therefore, its mode of recognition appears to be plant-specific.