ABSTRACT
During vegetative growth, biennial sugar beets maintain a steep gradient between the shoot (source) and the sucrose-storing taproot (sink). To shift from vegetative to generative growth, they require a chilling phase, called vernalization. Here, we studied sugar beet sink-source dynamics upon cold temperature-induced vernalization and revealed a pre-flowering taproot sink to source reversal. This transition is induced by transcriptomic and functional reprogramming of sugar beet tissue, resulting in a reversal of flux direction in long distance transport system, the phloem. As a key process for this transition, vacuolar sucrose importers and exporters, BvTST2;1 and BvSUT4, are oppositely regulated, leading to re-mobilization of sugars from taproot storage vacuoles. Concomitant changes in the expression of floral regulator genes suggest that the now deciphered processes are a prerequisite for bolting. Our data may thus serve dissecting metabolic and developmental triggers for bolting, which are potential targets for genome editing or breeding approaches.
Footnotes
One-sentence summary: Cold treatment transforms sugar beet (Beta vulgaris) taproots from sucrose-storing sink organs to sucrose-mobilizing source organs prior to bolting.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the instructions for Authors (www.plantcell.org) is: Benjamin Pommerrenig (pommerre{at}bio.uni-kl.de).