Updated project metadata. Autophagy, involved in protein degradation and amino acid recycling, plays a key role in plant development and stress responses. However, the relationship between autophagy and phytohormones is unclear. We used diverse methods, including CRISPR/Cas9, UPLC-MS/MS, chromatin immunoprecipitation, electrophoretic mobility shift assays, and dual-luciferase assays to explore the molecular mechanism of strigolactones in regulating autophagy and the degradation of ubiquitinated proteins under cold stress in tomato. We show that cold stress induced the accumulation of ubiquitinated proteins. Mutants deficient in strigolactone biosynthesis were more sensitive to cold stress with a higher accumulation of ubiquitinated proteins, while treatment with the synthetic strigolactone analog GR245DS enhanced cold tolerance in tomato, with a higher accumulation of autophagosomes and transcripts of autophagy-related genes (ATGs), and a lower accumulation of ubiquitinated proteins. Meanwhile, cold stress induced ELONGATED HYPOCOTYL 5 (HY5) accumulation, which was triggered by strigolactones. HY5 further trans-activated ATG18a promoter, resulting in autophagy formation. Mutation of ATG18a compromised strigolactone-induced cold tolerance, followed by a decreased formation of autophagosomes and an increased accumulation of ubiquitinated proteins. These findings reveal that strigolactones positively regulate autophagy in an HY5-dependent manner and promote the degradation of ubiquitinated proteins under cold conditions in tomato.