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The MaEIL9-MaZIP5-MaSCL8 module integrates MaBEL1 and synergistically modulates banana fruit ripening
Fan Liu1, Xueli Sun2, Ou Sheng2
1Institute of Fruit Tree Research, Guangdong Academy of Agricultural Sciences, Key Laboratory of South Subtropical Fruit Biology and Genetic Resource Utilization (Ministry of Agriculture and Rural Affairs), Guangdong Provincial Key Laboratory of Science and Technology Research on Fruit Tree, Guangzhou 510640, China; College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Introduction:
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.
Objectives:
This research was designed to elucidate the regulatory mechanism of MaSCL8 controlling banana ripening processes.
Methods:
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.
Results:
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.
Conclusion:
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.
