Disruption of the Sugar Transporters AtSWEET11 and AtSWEET12 Affects Vascular Development and Freezing Tolerance in Arabidopsis

In plants, the transport of sugars from the site of biosynthesis to the site of utilization or storage relies on sugar transporters located in different subcellular compartments and different vascular cell types. The SWEET sugar transporter family is one such class and is represented by 17 members in Arabidopsis. AtSWEET1 was the first plant SWEET transporter to be characterized; it acts as a glucose uniporter in multiple systems (Chen et al., 2010). AtSWEET11 and AtSWEET12 were subsequently identified as key players in sucrose efflux from phloem parenchyma cells, a prerequisite for phloem loading by import into the sieve element–companion cell complex (Chen et al., 2012), whereas AtSWEET16 and AtSWEET17 probably export fructose out of the vacuole and contribute significantly to the regulation of fructose levels in Arabidopsis (Chardon et al., 2013; Klemens et al., 2013; Guo et al., 2014).