Tomato SlSTK is involved in glucose response and regulated by the ubiquitin ligase SlSINA4.

Glucose signaling plays an essential role in plant growth, development and stress response. Previous studies have shown that STOREKEEPER (STK) is a new class of DNA binding protein that regulates patatin expression in potato tubers and confers elevated sensitivity to glucose response in Arabidopsis thaliana. However, the biological functions of STK gene in tomato (Solanum lycopersicum) have not been studied. Here, we characterized the tomato SlSTK and determined its role in glucose signaling. The SlSTK protein was localized in the nucleus and the expression of the SlSTK gene was induced by the glucose treatment. Overexpression of SlSTK in tomato enhanced glucose sensitivity, as manifested by reduced seed germination rate and arrested growth at the early seedling stage. In contrast, the SlSTK-knockout plants generated via the clustered regularly interspaced short palindromic repeats (CRISPR) - CRISPR-associated protein 9 (CRISPR-Cas9) technique attenuated the sensitivity to glucose. In addition, SlSTK was ubiquitinated in plant cells and interacted with the tomato ubiquitin ligase SEVEN IN ABSENTIA4 (SlSINA4) that degrades SlSTK in a ligase-dependent manner. Taken together, these results suggest that SlSTK is involved in glucose signaling and its stability is regulated by the ubiquitin ligase SlSINA4.