The MaEIL9-MaZIP5–MaSCL8 module integrates MaBEL1 and synergistically modulates banana fruit ripening

Recently, the plant-specific transcription factors GAI-RGA- and −SCRs (GRASs) have been linked to the modulation of the fruit ripening. Here, we present a regulatory model of banana fruit ripening controlled by GRAS TF MaSCL8. MaSCL8 is upregulated during fruit ripening and modulated by ethylene. MaSCL8 directly binds to the promoter regions of M aAMY3, MaBAM9b, MaEXPA15 , and MaEXP21 , activating their expression to drive starch and cell wall degradation during fruit ripening. Moreover, MaSCL8 physically interacts with MaBEL1 to assemble a functional protein complex that amplifies the transcriptional activation of their downstream targets. In addition, MaSCL8 was shown to be positively modulated by MabZIP5. Our findings provide important molecular insights for improving fruit quality and modifying fruit shelf life. • An ethylene-inducible GRASs transcription factor MaSCL8 act as a nucleus-localized transcription activator. • MaSCL8 directly activates the transcription of genes related to ethylene biosynthesis, starch degradation and cell wall disassembly. • MaSCL8 recruits ethylene-inducible MaBEL1 to enhance its regulation to its target genes. • Overexpression of MaSCL8 promotes tomato and banana fruit ripening. • The expression of MaSCL8 was directly activated by the MaEIL9-MaZIP5 module in response to ethylene. Fruit ripening is a genetically predetermined developmental process that is governed by a complex multilevel regulatory network requiring the orchestration of spatiotemporal expression of many genes and proteins. The GAI-RGA- and −SCRs (GRASs) are plant-exclusive transcription factors, which play pivotal regulatory roles in modulating growth, developmental processes, and environmental stress adaptation. However, the functional characterization and molecular mechanisms of GRASs in fruit ripening regulation remain poorly understood. This research was designed to elucidate the regulatory mechanism of MaSCL8 controlling banana ripening processes. Yeast one-hybrid assay, dual luciferase reporter assay, and electrophoretic mobility shift assay were used to look for downstream target genes and upstream regulators of MaSCL8 . We further performed luciferase complementation imaging and yeast two-hybrid assays to screen and verify MaSCL8-interacting proteins. Finally, the function of MaSCL8 was analyzed by stable overexpression in tomato and transient overexpression in banana. This study demonstrated that a GRAS gene, MaSCL8 , positively regulates banana fruit ripening. MaSCL8 functioned as a nuclear-localized transcriptional activator and could physically interact with the promoter regions of MaAMY3 , MaBAM9b , MaEXPA15 , MaEXP21 , MaPL3 , and MaACO1, consequently enhancing their transcription. MaSCL8 overexpression in tomato and banana accelerated ripening processes by inducing the transcription of ethylene biosynthesis and softening related genes. Interestingly, MaBEL1 formed a heterodimer with MaSCL8, enhancing the MaSCL8-activated transcription of its target genes. In addition, we found that MaEIL9-MabZIP5 transcriptional cascade act upstream of MaSCL8 and activate the expression of MaSCL8 by physically interacting with its promoter. Our findings indicate the MaEIL9–MaZIP5–MaSCL8 module cooperates with MaBEL1, contributing to banana ripening by improving ethylene production, starch degradation and cell wall disassembly. These results advance the fundamental understanding of GRAS-mediated ripening mechanisms.