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      Re-evaluation of the nor mutation and the role of the NAC-NOR transcription factor in tomato fruit ripening


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          The 186 aa truncated protein produced by the tomato spontaneous non-ripening ( nor) mutant enters the nucleus and combines with the promoters of its target genes, resulting in a gain of function.


          The tomato non-ripening ( nor) mutant generates a truncated 186-amino-acid protein (NOR186) and has been demonstrated previously to be a gain-of-function mutant. Here, we provide more evidence to support this view and answer the open question of whether the NAC-NOR gene is important in fruit ripening. Overexpression of NAC- NOR in the nor mutant did not restore the full ripening phenotype. Further analysis showed that the truncated NOR186 protein is located in the nucleus and binds to but does not activate the promoters of 1-aminocyclopropane-1-carboxylic acid synthase2 ( SlACS2), geranylgeranyl diphosphate synthase2 ( SlGgpps2), and pectate lyase ( SlPL), which are involved in ethylene biosynthesis, carotenoid accumulation, and fruit softening, respectively. The activation of the promoters by the wild-type NOR protein can be inhibited by the mutant NOR186 protein. On the other hand, ethylene synthesis, carotenoid accumulation, and fruit softening were significantly inhibited in CR-NOR (CRISPR/Cas9-edited NAC-NOR) fruit compared with the wild-type, but much less severely affected than in the nor mutant, while they were accelerated in OE-NOR (overexpressed NAC-NOR) fruit. These data further indicated that nor is a gain-of-function mutation and NAC-NOR plays a significant role in ripening of wild-type fruit.

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          Most cited references54

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          Transient expression vectors for functional genomics, quantification of promoter activity and RNA silencing in plants

          Background We describe novel plasmid vectors for transient gene expression using Agrobacterium, infiltrated into Nicotiana benthamiana leaves. We have generated a series of pGreenII cloning vectors that are ideally suited to transient gene expression, by removing elements of conventional binary vectors necessary for stable transformation such as transformation selection genes. Results We give an example of expression of heme-thiolate P450 to demonstrate effectiveness of this system. We have also designed vectors that take advantage of a dual luciferase assay system to analyse promoter sequences or post-transcriptional regulation of gene expression. We have demonstrated their utility by co-expression of putative transcription factors and the promoter sequence of potential target genes and show how orthologous promoter sequences respond to these genes. Finally, we have constructed a vector that has allowed us to investigate design features of hairpin constructs related to their ability to initiate RNA silencing, and have used these tools to study cis-regulatory effect of intron-containing gene constructs. Conclusion In developing a series of vectors ideally suited to transient expression analysis we have provided a resource that further advances the application of this technology. These minimal vectors are ideally suited to conventional cloning methods and we have used them to demonstrate their flexibility to investigate enzyme activity, transcription regulation and post-transcriptional regulatory processes in transient assays.
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            A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening.

            A major component in the regulatory network controlling fruit ripening is likely to be the gene at the tomato Colorless non-ripening (Cnr) locus. The Cnr mutation results in colorless fruits with a substantial loss of cell-to-cell adhesion. The nature of the mutation and the identity of the Cnr gene were previously unknown. Using positional cloning and virus-induced gene silencing, here we demonstrate that an SBP-box (SQUAMOSA promoter binding protein-like) gene resides at the Cnr locus. Furthermore, the Cnr phenotype results from a spontaneous epigenetic change in the SBP-box promoter. The discovery that Cnr is an epimutation was unexpected, as very few spontaneous epimutations have been described in plants. This study demonstrates that an SBP-box gene is critical for normal ripening and highlights the likely importance of epialleles in plant development and the generation of natural variation.
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              A MADS-box gene necessary for fruit ripening at the tomato ripening-inhibitor (rin) locus.

              Tomato plants harboring the ripening-inhibitor (rin) mutation yield fruits that fail to ripen. Additionally, rin plants display enlarged sepals and loss of inflorescence determinacy. Positional cloning of the rin locus revealed two tandem MADS-box genes (LeMADS-RIN and LeMADS-MC), whose expression patterns suggested roles in fruit ripening and sepal development, respectively. The rin mutation alters expression of both genes. Gene repression and mutant complementation demonstrate that LeMADS-RIN regulates ripening, whereas LeMADS-MC affects sepal development and inflorescence determinacy. LeMADS-RIN demonstrates an agriculturally important function of plant MADS-box genes and provides molecular insight into nonhormonal (developmental) regulation of ripening.

                Author and article information

                Role: Editor
                J Exp Bot
                J. Exp. Bot
                Journal of Experimental Botany
                Oxford University Press (UK )
                22 June 2020
                27 April 2020
                27 April 2020
                : 71
                : 12
                : 3560-3574
                [1 ] Laboratory of Fruit Biology, College of Food Science & Nutritional Engineering, China Agricultural University , Beijing, China
                [2 ] College of Agriculture & Biotechnology, Zhejiang University , Hangzhou, China
                [3 ] State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources/Guangdong Provincial Key Laboratory of Postharvest Science of Fruits and Vegetables, College of Horticulture, South China Agricultural University , Guangzhou, China
                [4 ] School of Food and Chemical Engineering, Beijing Technology and Business University , Beijing, China
                [5 ] Plant Sciences Division, School of Biosciences, University of Nottingham , Sutton Bonington Campus, Loughborough, UK
                [6 ] Department of Pomology, Faculty of Agriculture, University of Zagreb , Zagreb, Croatia
                [7 ] Department of Plant Sciences, University of California , Davis, CA, USA
                [8 ] Crops Pathology and Genetics Research Unit, United States Department of Agriculture , Agricultural Research Service, Davis, CA, USA
                [9 ] Fondazione Edmund Mach , Italy
                Author notes
                Author information
                © The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                : 29 August 2019
                : 02 March 2020
                : 25 March 2020
                : 27 April 2020
                Page count
                Pages: 15
                Funded by: National Natural Science Foundation of China, DOI 10.13039/501100001809;
                Award ID: 31571898
                Award ID: 31972129
                Award ID: 31772029
                Award ID: 31572173
                Research Papers
                Growth and Development

                Plant science & Botany
                crispr/cas9,gene function,nac-nor,nor mutant,tomato fruit ripening,transcription factor


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