MaSPL16 positively regulates fruit ripening in bananas via the direct transcriptional induction of MaNAC029

Abstract

Fruit ripening (FR) is attributed to the selective expression of several genes precisely governed by various specific transcription factors (TFs). The NAC (NAM, ATAF, and CUC) TF, MaNAC029, positively regulated banana ripening by directly inducing ethylene biosynthesis and transcription of fruit quality-related genes. However, its upstream regulatory mechanism still needs to be clarified. Herein, yeast one-hybrid screening revealed that a SQUAMOSA promoter binding protein-like (SPL) TF, MaSPL16, was a potentially upstream regulator of Musa acuminata NAC (NAM, ATAF, CUC) 029 (MaNAC029). Furthermore, gel mobility shift assay revealed that MaSPL16 can directly bound with the “GTAC” element of the MaNAC029 promoter. The gene expression and promoter activity assays demonstrated that Musa acuminata SPL (SQUAMOSA promoter binding protein-like) 16 (MaSPL16) expression was inducible by ethylene and ripening. MaSPL16 was localized to the nucleus, displayed a potenial capacity for transcriptional activation of MaNAC029. More critically, the transient expression of MaSPL16 in bananas accelerated FR via the upregulation of MaNAC029 and its downstream genes. Collectively, the mechanistic basis of a regulatory cascade involving MaSPL16-MaNAC029 that governed ethylene biosynthesis and fruit quality throughout the entire process of banana fruit ripening was unveiled. These outcomes increase the understanding of the gene-transcriptional regulatory mechanisms in FR. They are envisaged to help devise molecular techniques to regulate maturation and improve future fruit quality.