Mutations at <i>CRE1</i> impair cytokinin‐induced repression of phosphate starvation responses in <i>Arabidopsis</i>

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<jats:title>Summary</jats:title><jats:p>Plants display a number of responses to low phosphate availability, involving biochemical and developmental changes. Recently we have shown that many of these responses can be repressed in roots by exogenous addition of cytokinins. In order to understand the genetic basis to this effect of cytokinins, and its relation with the better known roles of cytokinins in the control of cell‐cycle and differentiation, we have undertaken mutant screening and characterization using a transgenic line of <jats:italic>Arabidopsis thaliana</jats:italic> harbouring a reporter gene specifically responsive to Pi starvation (<jats:italic>AtIPS1::GUS</jats:italic>). One type of mutant identified displayed reduced sensitivity of <jats:italic>AtIPS1::GUS</jats:italic> to cytokinin repression. Several other Pi starvation response genes showed reduced cytokinin sensitivity in these lines. These mutants also showed reduced cytokinin repression of the anthocyanin accumulation induced by Pi starvation in the aerial part of the plants. Mapping and molecular characterization of these mutants showed that they were allelic of <jats:italic>CRE1/WOL</jats:italic>, a locus known to encode a cytokinin receptor. <jats:italic>CRE1</jats:italic> is downregulated by Pi starvation and induced by cytokinins, both in the wild‐type and in the <jats:italic>cre1</jats:italic> mutant<jats:italic>s,</jats:italic> in which <jats:italic>cre1</jats:italic> mRNA levels are higher. These results reveal the existence of a positive feed‐back loop, in addition to the already established negative feedback loop, in cytokinin signalling and indicate that the negative regulation of Pi starvation responses by cytokinins involves a two‐component signalling circuitry, as it is the case of other types of cytokinin response.</jats:p>

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