The study shows that these two regulators not only act on their own target genes, but also physically interact and jointly strengthen each other's effects, forming a cooperative module that links hormone signaling with sugar formation during ripening. This finding offers a clearer molecular explanation for how bananas develop sweetness and desirable eating quality after harvest, and it may support future strategies to better control ripening, improve fruit quality, and reduce postharvest losses in commercial banana supply chains.
Fruit ripening in climacteric crops such as banana is already known to depend heavily on ethylene, which triggers major changes in color, texture, aroma, and taste. Previous studies have shown that NAC transcription factors are key regulators in these processes, and earlier work had separately identified MaNAC029 as a regulator of ethylene biosynthesis genes and MaNAC19 as a regulator of the sucrose synthesis gene MaSPS1. However, fruit ripening is controlled by complex transcriptional networks rather than isolated factors, and the functional relationship between these two NAC proteins had remained unclear. That gap limited understanding of how ethylene signaling and sugar accumulation are coordinated during ripening, making it necessary to investigate whether MaNAC029 and MaNAC19 act independently or as part of an integrated regulatory system.
A study (DOI: 10.48130/ph-0025-0029) published in Plant Hormones on 27 January 2026 by Wei Shan, South China Agricultural University, shows that MaNAC029 and MaNAC19 form a cooperative transcriptional module that jointly activates genes for ethylene biosynthesis and sucrose metabolism during banana ripening.
The researchers first monitored banana fruit during ethylene-induced postharvest ripening and measured peel color, endogenous ethylene production, firmness, sucrose content, and gene expression. As ripening progressed, the peel turned from green to yellow, ethylene production rose and peaked early, firmness declined, and sucrose content increased markedly. Importantly, expression of MaNAC029 and MaNAC19 followed highly similar patterns, both peaking with the ethylene burst, suggesting coordinated roles in ripening. The team then tested whether the proteins interact. Using yeast two-hybrid assays, bimolecular fluorescence complementation in tobacco BY-2 protoplasts, and co-immunoprecipitation in tobacco leaves, they confirmed that MaNAC029 physically interacts with MaNAC19 in the nucleus. Next, electrophoretic mobility shift assays showed that MaNAC029 directly binds the promoter of MaSPS1, a key sucrose phosphate synthase gene, while MaNAC19 directly binds the promoters of MaACO1 and MaACO13, two genes involved in ethylene biosynthesis. Dual-luciferase transient expression assays further demonstrated that each factor could activate these target promoters. Most notably, when both transcription factors were expressed together, promoter activation became significantly stronger than with either factor alone. This synergistic effect showed that the two NAC proteins do not simply regulate parallel pathways; instead, they reinforce one another to couple ethylene production with sugar accumulation. The resulting model proposes that during ripening, the MaNAC029–MaNAC19 complex amplifies feedback ethylene synthesis through MaACO1/13 while simultaneously promoting sucrose formation through MaSPS1, thereby helping drive both ripening progression and fruit quality development.
Overall, the study identifies MaNAC029 and MaNAC19 as a central banana ripening module that integrates hormonal and metabolic control. By revealing how these two transcription factors cooperate to regulate both ethylene biosynthesis and sucrose synthesis, the work advances understanding of the molecular basis of banana quality formation after harvest. The findings also provide a useful framework for future research on stress-responsive ripening regulation and may eventually contribute to breeding or postharvest technologies aimed at improving sweetness, shelf life, and market value in banana fruit.
