Vernalization Alters Sink and Source Identities and Reverses Phloem Translocation from Taproots to Shoots in Sugar Beet
Cristina Martins Rodrigues, Christina Müdsam, Isabel Keller, Wolfgang Zierer, Olaf Czarnecki, José M. Miguel del Corral, F. Reinhardt, Petra Nieberl, Karin Fiedler‐Wiechers, Frederik Sommer, Michael Schroda, Timo Mühlhaus, Karsten Harms, Ulf‐Ingo Flügge, Uwe Sonnewald, Wolfgang Koch, Frank Ludewig, H. Ekkehard Neuhaus, Benjamin Pommerrenig
Abstract
) maintains a steep Suc concentration gradient between the shoot (source) and the taproot (sink). To shift from vegetative to generative growth, they require a chilling phase known as vernalization. We studied sugar beet sink-source dynamics upon vernalization and showed that before flowering, the taproot underwent a reversal from a sink to a source of carbohydrates. This transition was induced by transcriptomic and functional reprogramming of sugar beet tissue, resulting in a reversal of flux direction in the phloem. In this transition, the vacuolar Suc importers and exporters TONOPLAST SUGAR TRANSPORTER2;1 and SUCROSE TRANSPORTER4 were oppositely regulated, leading to the mobilization of sugars from taproot storage vacuoles. Concomitant changes in the expression of floral regulator genes suggest that these processes are a prerequisite for bolting. Our data will help both to dissect the metabolic and developmental triggers for bolting and to identify potential targets for genome editing and breeding.