HFR1 delays dark-induced leaf senescence by suppressing ORE1 transcription and attenuating its protein activity

Leaf senescence is a complex physiological process that involves the gradual wilting and death of leaf tissue. While multiple transcription factors (TFs) contribute to this process, the NAC TF ORESARA1 (ORE1) plays a major role in leaf senescence in Arabidopsis (Arabidopsis thaliana). ORE1 is regulated by various upstream TFs, including PHYTOCHROME INTERACTING FACTOR5 (PIF5), which directly activates ORE1 transcription. Here, we show that LONG HYPOCOTYL IN FAR-RED1 (HFR1), an atypical basic helix-loop-helix TF primarily involved in light signaling, functions in the leaf senescence regulatory network. Under aging- and dark-induced leaf senescence treatments, HFR1 overexpression delayed leaf senescence like the ore1 mutation, whereas hfr1 displayed early leaf senescence like ORE1 overexpression. This finding was supported by HFR1 reducing the expression of senescence and chlorophyll degradation genes, ORE1, and ORE1 target genes. HFR1 also rescued the early senescence phenotype of ORE1 overexpression, indicating that HFR1 suppresses ORE1. Notably, HFR1 directly interacted with ORE1 to suppress its DNA-binding ability, thereby inhibiting its function as a TF. Furthermore, HFR1 and ORE1 regulated several genes related to leaf senescence in an antagonistic manner. HFR1 also inhibited PIF5 from directly activating the expression of ORE1 and other senescence-related genes. Our findings demonstrate that HFR1 delays leaf senescence by suppressing ORE1 through multiple pathways.