Cytokinin is required for escape but not release from auxin mediated apical dominance

<jats:title>Summary</jats:title><jats:p>Auxin produced by an active primary shoot apex is transported down the main stem and inhibits the growth of the axillary buds below it, contributing to apical dominance. Here we use <jats:italic>Arabidopsis thaliana</jats:italic> cytokinin (<jats:styled-content style="fixed-case">CK</jats:styled-content>) biosynthetic and signalling mutants to probe the role of <jats:styled-content style="fixed-case">CK</jats:styled-content> in this process. It is well established that bud outgrowth is promoted by <jats:styled-content style="fixed-case">CK</jats:styled-content>, and that <jats:styled-content style="fixed-case">CK</jats:styled-content> synthesis is inhibited by auxin, leading to the hypothesis that release from apical dominance relies on an increased supply of <jats:styled-content style="fixed-case">CK</jats:styled-content> to buds. Our data confirm that decapitation induces the expression of at least one <jats:styled-content style="fixed-case">ISOPENTENYLTRANSFERASE</jats:styled-content> (<jats:italic><jats:styled-content style="fixed-case">IPT</jats:styled-content></jats:italic>) <jats:styled-content style="fixed-case">CK</jats:styled-content> biosynthetic gene in the stem. We further show that transcript abundance of a clade of the <jats:styled-content style="fixed-case">CK</jats:styled-content>‐responsive type‐A Arabidopsis response regulator (<jats:italic><jats:styled-content style="fixed-case">ARR</jats:styled-content></jats:italic>) genes increases in buds following <jats:styled-content style="fixed-case">CK</jats:styled-content> supply, and that, contrary to their typical action as inhibitors of <jats:styled-content style="fixed-case">CK</jats:styled-content> signalling, these genes are required for <jats:styled-content style="fixed-case">CK</jats:styled-content>‐mediated bud activation. However, analysis of the relevant <jats:italic>arr</jats:italic> and <jats:italic>ipt</jats:italic> multiple mutants demonstrates that defects in bud <jats:styled-content style="fixed-case">CK</jats:styled-content> response do not affect auxin‐mediated bud inhibition, and increased <jats:italic><jats:styled-content style="fixed-case">IPT</jats:styled-content></jats:italic> transcript levels are not needed for bud release following decapitation. Instead, our data suggest that <jats:styled-content style="fixed-case">CK</jats:styled-content> acts to overcome auxin‐mediated bud inhibition, allowing buds to escape apical dominance under favourable conditions, such as high nitrate availability.</jats:p>