In fed cells， syntaxin 17 (Stx17) is associated with microtubules at the endoplasmic reticulum-mitochondria interface and promotes mitochondrial fission by determining the localization and function of the mitochondrial fission factor Drp1. Upon starvation， Stx17 dissociates from microtubules and Drp1， and binds to Atg14L， a subunit of the phosphatidylinositol 3-kinase complex， to facilitate phosphatidylinositol 3-phosphate production and thereby autophagosome formation， but the mechanism underlying this phenomenon remains unknown. Here we identify MAP1B-LC1 (microtubule-associated protein 1B-light chain 1) as a critical regulator of Stx17 function. Depletion of MAP1B-LC1 causes Stx17-dependent autophagosome accumulation even under nutrient-rich conditions， whereas its overexpression blocks starvation-induced autophagosome formation. MAP1B-LC1 links microtubules and Stx17 in fed cells， and starvation causes the dephosphorylation of MAP1B-LC1 at Thr217， allowing Stx17 to dissociate from MAP1B-LC1 and bind to Atg14L. Our results reveal the mechanism by which Stx17 changes its binding partners in response to nutrient status.