Fig. 7

Possible regulatory mechanisms that circRNAs involved in the root of cucumber during salt stress. a Cucumber plant. b Root system is the first plant organ that senses excess Na⁺, which triggers downstream stress responses. c Function annotation of parent gene and mRNA targeted by miRNAs suggested that circRNAs participate in salt-induced physiological and biochemical response including ① Ion homeostasis regulation (e.g. CHX, KEA, NHX), ② activation of abscisic acid (ABA) pathways and osmotic stress signaling (SnRK2s, PP2C, MYB, SBP et al.), ③ biosynthesis and accumulation of compatible osmolytes (proline, sucrose), and ④ physical and chemical alterations of cell wall (cellulose synthase, sucrose synthase, xyloglucan glycosyltransferase; FRAGILE FIBER 3). d The schematic summary presents expression levels of circRNAs and proline metabolism-related genes, and P5CS, ProDH activities and proline content with significant differences between treatments. Values are presented as the means of six replicates ± SE. CHX, cation/H⁺ exchanger-like; KEA, K⁺ efflux antiporter-like; NHX, Na+/H+ exchanger-like; SnRK2s, SNF1-related kinases; PP2C, protein phosphatase 2C; P5CS, D1-pyrroline-5-carboxylate synthetase; PDH, proline dehydrogenase