Acts as a negative regulator of fumonisin B1- and pathogen-induced programmed cell death (PCD), and regulates pathogen-induced symptom development (PubMed:25862728). May function redundantly with CYCLASE2 for normal plant growth, development and viability (Probable). Induced by salicylate. No visible phenotype under normal growth conditions, but leaves of mutant plants exhibit a severly increased cell death when exposed to fumonisin B1 or a bacterial pathogen that triggers the defensive hypersensitive cell death. The double mutants cyclase1 and cyclase2 are embryonic lethal. Belongs to the Cyclase 1 superfamily.