Tomatoes get sweeter when a sugar-export protein is switched off
Song B, Kang Y, Zheng X, Li Z, Cheng Y
Crispr
The tomatoes ripening on your patio vines owe their sweetness to a tug-of-war inside their cells between proteins that hoard sugar and ones that let it leak away, and this study just revealed how to tip that balance.
Tomato fruit cells have a tiny gatekeeper protein that pumps sugar out of the cell, which sounds counterproductive if you want a sweet tomato. Researchers discovered two teams of proteins fight over this gatekeeper: one team stabilizes it (keeping sugar leaking out, fruit less sweet), and the other team tags it for destruction (letting sugar accumulate, fruit sweeter). When they used gene editing to remove the gatekeeper protein entirely, the tomatoes ended up noticeably sweeter, showing plant breeders a promising target for tastier fruit.
Key Findings
SlSWEET16 is a plasma-membrane sugar transporter that exports mono- and disaccharides out of tomato fruit cells, and CRISPR/Cas9 knockout of the gene increases fruit sugar accumulation
Two kinases (SlSnRK2.3 and SlSnRK2.4) phosphorylate SlSWEET16's C-terminus to stabilize the protein and suppress fruit sugar buildup, while the E3 ubiquitin ligase SlTT3.1L2 ubiquitinates it to destabilize the protein and promote sugar accumulation
Mutating the specific phosphorylated or ubiquitinated residues on SlSWEET16's C-terminus directly altered protein stability and fruit sugar levels, confirming the dual post-translational control mechanism
chevron_right Technical Summary
Scientists found the molecular switch that controls how much sugar builds up in tomato fruit, discovering that two competing chemical tags on a sugar-transport protein decide whether sugar stays in the fruit or leaks out. Turning off the transporter gene made tomatoes sweeter, pointing to a new way to breed better-tasting produce.
Abstract Preview
Original paper
Phosphorylation and ubiquitination coordinate homeostasis of a tomato transporter responsible for fruit sugar accumulation.
Sugar transport mediated by different transporters is essential for maintaining sugar homeostasis in plants. Here, we report that phosphorylation and ubiquitination coordinate the homeostasis of a ...
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