Abstract
Sugars, especially glucose and fructose, contribute to the taste and quality of tomato fruits. These compounds are translocated from the leaves to the fruits and then unloaded into the fruits by various sugar transporters at the plasma membrane. SWEETs, are sugar transporters that regulate sugar efflux independently of energy or pH. To date, the role of SWEETs in tomato has received very little attention. In this study, we performed functional analysis of SlSWEET7a and SlSWEET14 to gain insight into the regulation of sugar transport and storage in tomato fruits. SlSWEET7a and SlSWEET14 were mainly expressed in peduncles, vascular bundles, and seeds. Both SlSWEET7a and SlSWEET14 are plasma membrane-localized proteins that transport fructose, glucose, and sucrose. Apart from the resulting increase in mature fruit sugar content, silencing SlSWEET7a or SlSWEET14 resulted in taller plants and larger fruits (in SlSWEET7a-silenced lines). We also found that invertase activity and gene expression of some SlSWEET members increased, which was consistent with the increased availability of sucrose and hexose in the fruits. Overall, our results demonstrate that suppressing SlSWEET7a and SlSWEET14 could be a potential strategy for enhancing the sugar content of tomato fruits.
Highlights
In higher plants, photosynthesis is the process by which carbon and energy and transformed into sugars in source tissues
SlSWEET1e and SlSWEET3 belong to clade I, whose members are involved in glucose import[7,30,32], while SlSWEET7a and SlSWEET14 belong to clade II and clade III, respectively; the functions of these two clades have not yet been identified in tomato
The results showed that the expression of SlSWEET7a and SlSWEET14 restored the growth of EBY.VW4000 on media supplemented with glucose or fructose (Fig. 4a)
Summary
Photosynthesis is the process by which carbon and energy and transformed into sugars in source tissues. These sugars are exported to various sink tissues and organs to support normal growth and development[1]. Sugars are an important nutritional component, especially in fruit crop species, and the accumulation of soluble sugars somewhat determines the quality of fruits. Sugar transport and storage are essential for Sucrose is unloaded from the phloem to the fruit apoplast, where it can be either directly transported into storage parenchyma cells by sucrose transporters (SUTs) through the extracellular pathway or hydrolyzed to glucose and fructose by extracellular invertase and transported into parenchyma cells by hexose transporters[10,11].
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