Abstract
Fragaria chiloensis is a strawberry endemic from Chile with attractive white-pink fruit, pleasant aroma and taste. However, this fruit has a limited post-harvest period due to fast softening. Several transcription factors (TFs) are involved in the regulation of fruit ripening, and members of the NAC family have been implicated in cell wall remodeling. FcNAC1 was isolated from F. chiloensis fruit, coding a protein of 332 amino acid residues and displaying a characteristic NAC domain at the N terminus. FcNAC1 protein showed nuclear localization. An increase in transcript level was observed during ripening. A sequence of 1488 bp of FcNAC1 promoter was obtained. In silico analysis identified cis elements able to respond to some hormones and Secondary wall NAC binding elements (SNBE), and responding to auxin and ABA. A structural model of FcNAC1 provided evidence for interaction with DNA sequences containing SNBE, while a dual luciferase assay confirmed the transcriptional activation by FcNAC1 of the promoter of FcPL, a gene involved in cell wall remodeling in F. chiloensis fruit. The results suggest the participation of FcNAC1 during ripening development of strawberry fruit, by regulating pectin metabolism during softening.
Highlights
IntroductionThe fruit ripening process comprises a highly coordinated, irreversible and genetically programmed event which involves many biochemical, physiological and organoleptic modifications that lead to the development of a soft and edible ripe fruit with ideal quality features
151 in rice, 79 in grape, 26 in citrus, 163 in poplar, 152 in soybean and 152 in tobacco[20,21,22,23]. These transcription factors (TFs) share a NAC domain consisting of 130–150 amino acids at their N-terminus that allows for their interaction with DNA, which is divided into five subdomains, A–E, from N-terminus to C-terminus respectively[24]
The characterization of the F. chiloensis NAC transcription factor, named FcNAC1, revealed a protein sharing a highly conserved NAC domain and a variable C-terminal region that can act as a domain of transcriptional activation
Summary
The fruit ripening process comprises a highly coordinated, irreversible and genetically programmed event which involves many biochemical, physiological and organoleptic modifications that lead to the development of a soft and edible ripe fruit with ideal quality features This is concomitant with various changes such as chlorophyll degradation, carotenoid or anthocyanin biosynthesis, increased respiration, essential oils, flavor and aroma components, increased activity of cell wall-degrading enzymes, and transient increases in hormonal production that take place during fruit ripening[6]. NAC genes are a transcription factor family (TF), which have been found to play important roles in plant development and environmental responses Members of this family have been reported to be involved in the ripening and softening of fleshy fruits such as citrus[10], banana[11], tomato[12], and peach[13]. The activation of secondary wall biosynthetic genes is modulated by a transcriptional network, including secondary wall NAC (SWN) master switches and their downstream transcription factors[29]
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