Phosphoenolpyruvate carboxylase activation by reversible phosphorylation in white lupin cluster roots

Phosphoenolpyruvate carboxylase (PEPC) is a tightly regulated enzyme that controls carbohydrate partitioning to organic acid anions (malate, citrate) that are excreted in copious amounts by cluster (proteoid) roots of phosphate-deprived white lupin.

Representative image of normal and cluster roots in hydroponically cultivated Pi-deficient white lupin plants. The tips of the secondary lateral roots and unbranched proximal root denote the normal roots. Developmental stages of CRs are labelled according to the number of days following rootlet emergence: juvenile (1–3 d), mature (4–6 d), senescing (7–9 d) and senesced (≥10 d). Scale bar = 35 mm.

Shane et al. establish a novel mechanistic link between reversible, light-dependent activation of PEPC by in vivo phosphorylation, and the concentrations of sucrose, and its signalling metabolite trehalose-6-phosphate in lupin cluster roots. PEPC’s phosphorylation is correlated with enhanced rates of root organic anion exudation and phosphate uptake, and appears to be modulated by sucrose translocated from illuminated CO2-fixing leaves into the non-photosynthetic cluster roots.

This paper is part of the Root Biology Special Issue.