Auxin Response Factors and Aux/IAA Proteins Potentially Control –S Responsive Expression of SULTR1;1

Abstract

Sulfur is an essential nutrient for plants and its deficiency (−S) severely affects plant growth. To acquire limited sulfur under –S, plants have evolved signal transduction pathways resulting in enhanced sulfate uptake and assimilation. The transcript level of the high affinity sulfate transporter SULTR1;1 is dramatically induced by –S. The –S-induced expression of SULTR1;1 is dependent on SLIM1 transcription factor which controls a broad range of –S responsive gene expression. Previously we identified the sulfur-responsive element of SULTR1;1 (SURE11) which includes a 6 bp sequence, GAGACA, identical to the binding sequence of auxin response factors (ARFs). ARFs are a family of transcription factors that promote or repress the expression of auxin responsive genes. The function of ARFs is inhibited by the hetero-dimerization with Aux/IAA proteins that cannot bind to the sequence. Though SULTR1;1 expression was not modulated by exogenously applied auxin, the identity between SURE-core sequence and the ARF binding sequence suggests that one of the ARF works to induce SULTR1;1 expression under –S. In this paper, we attempt to predict which ARFs and Aux/IAA proteins potentially control –S-induced expression of SULTR1;1 by using microarray data on slim1 and the parental plants. Five ARF and seven Aux/IAA proteins were up- or down-regulated by –S in parental plants. Among them, none of the ARF modified its –S response in slim1, but five Aux/IAA proteins lost their –S response in slim1, including IAA13 and IAA28 whose positive function in sulfur assimilation had been reported. These results indicated that this method could be useful in predicting candidates for regulatory genes working in –S responsive gene expression.