Snf1 and yeast GSK3-β activates Tda1 to suppress glucose starvation signaling

In budding yeast, the presence of glucose, a preferred energy source, suppresses the expression of respiration-related genes through a process known as glucose repression. Conversely, under glucose starvation conditions, Snf1 phosphorylates and activates downstream factors, relieving this repression and allowing cells to adapt. Recently, the Tda1 protein kinase has been implicated in these glucose starvation responses, although its function remains largely uncharacterized. In this study, we demonstrate that Snf1 and yeast glycogen synthase kinase 3-beta (GSK3-β) independently phosphorylate and activate Tda1, which in turn phosphorylates Hxk2 at Ser15. The Ser483 and Thr484 residues of Tda1 are critical for its activation by Snf1, while the Ser509 residue is crucial for its activation by yeast GSK3-β. Importantly, under glucose starvation conditions, the TDA1 deletion mutant shows increased expression of respiration-related genes and a faster growth rate compared to wild-type cells, which is opposite to what is observed in SNF1 and yeast GSK3-β deletion mutants. These findings suggest that Tda1 is activated by Snf1 and yeast GSK3-β, and functions as a suppressor of the glucose starvation signaling.