Integration of Environmental and Internal Cues for Triggering Vegetative Reproduction in Potato

Plants regulate their sexual and vegetative reproductive development by integrating external cues such as day length with internal cues such as the availability of assimilates. In potato, the formation of underground vegetative storage organs is regulated using a similar signal transduction pathway to the induction of flowering. At the same time, carbohydrate in the form sucrose has long been known to play a central role in tuber induction. We have now identified a novel mechanism by which the sucrose and photoperiod signaling pathways intersect. Using in silico co-regulation expression analysis, we have identified a set of genes that are tightly correlated. We have shown that one of these genes codes for a potato specific sucrose efflux carrier, belonging to the clade III, SWEET11 homologues. We have been able to show a physical interaction between a sucrose efflux carrier and the FT homologue and tuberigen peptide hormone StSP6A. Both in vivo and in vitro interaction experiments show that these two proteins interact in the plasma membrane. Coordinated and diametric expression in transgenic plants, produce tuberisation specific phenotypes that corroborate the interdependence and process specificity of these two proteins. For the first time, our data integrates the sugar dependent and light dependent pathways for tuber formation and helps in the understanding of the mechanisms of the switch from apoplastic to symplastic assimilate transport during the transition to tuberisation. The broader implication of our findings for the regulation of both sexual and vegetative reproduction will be discussed.