Low phosphate signaling induces changes in cell cycle gene expression by increasing auxin sensitivity in the Arabidopsis root system

Lateral root development is an important morphogenetic process in plants, which allows the modulation root architecture and substantially determines the plant''s efficiency for water and nutrient uptake. Postembryonic root development is under the control of both endogenous developmental programs and environmental stimuli. Nutrient availability plays a major role among environmental signals that modulate root development. Phosphate (Pi) limitation is a constraint for plant growth in many natural and agricultural ecosystems. Plants posses Pi-sensing mechanisms that enable them to respond and adapt to conditions of limited Pi supply, including increased formation and growth of lateral roots. Root developmental modifications are mainly mediated by the plant hormone auxin. Recently we showed that the alteration of root system architecture under Pi-starvation may be mediated by modifications in auxin sensitivity in root cells via a mechanism involving the TIR1 auxin receptor. In this addendum, we provide additional novel evidence indicating that the low Pi pathway involves changes in cell cycle gene expression. It was found that Pi deprivation increases the expression of CDKA, E2Fa, Dp-E2F and CyCD3. In particular, E2Fa, Dp-E2F and CyCD3 genes were specifically upregulated by auxin in Pi-deprived Arabidopsis seedlings that were treated with the auxin transport inhibitor NPA, indicating that cell cycle modulation by low Pi signaling is independent of auxin transport and dependent on auxin sensitivity in the root.Key words: phosphate signaling, auxin transport, auxin sensitivity, roots