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Genome-Level Investigation of WRKY Transcription Factors and Their Potential Roles in Fruit Peel Ripening and Coloration in the Common Fig (Ficus carica L.)

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Abstract

WRKY transcription factors (TFs) play significant roles in plant development. However, they have not yet been studied in terms of the impact they have on the common fig (Ficus carica L.), a significant fruit species in Mediterranean countries. In this study, we extensively examined the full-genome F. carica WRKY (FcWRKYs) gene complement (47 genes), in terms of gene structure, protein domains and motifs, physicochemical properties, phylogenetic relationships and selection pressure. Based on the structural properties of the encoded proteins, we grouped the FcWRKY genes into three main groups (I, II and III), with the second group being further divided into five subgroups (a–e). Subgroup IId FcWRKY proteins were discovered to contain the Plant zinc cluster (Plant-zn-clust) domain and Ca2+-dependent Calmodulin (CaM)-binding domain (CaMBD). In total, we discovered ten conserved motifs, seven of which may be associated with WRKY functional specificities attributable to a single group or a small number of groups. Phylogenetically related members shared similar exon–intron structure, with the average number of exons being higher (~ 5) in (sub)groups I, IIa, IIb compared to IIc, IId, IIe and III (~ 3). Comparative phylogeny using the mulberry WRKY gene complement (MnWRKYs) revealed 38 pairs of orthologous genes shared by both species, which diverged from 84.3 to 25.3 million years ago (Mya) and have been evolving under purifying selection that was weaker on group III genes, suggesting an important role of this group in the enlargement of the adaptive array of WRKY TFs. RNA-seq results revealed that genes that were highly expressed in the peel across all fruit developmental stages belonged to group I and subgroups IIb, IIc, IId and IIe, suggesting the role played by these members in fruit peel development. RT-qPCR validated this profile and further showed that three genes FcWRKY25 (IIc), FcWRKY31 (IIb), and FcWRKY39 (IIc) are clearly more overexpressed during color acquisition in the Tunisian dark cultivar ‘Zidi’, in comparison with the light purple cultivar ‘Soltani’, presenting these three genes as potential contributors to the changes in biochemical compounds in the fig peel during fruit maturation. The knowledge framework provided by our study will be a valuable asset in the functional exploration of candidate genes that may be associated with fruit quality.

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Acknowledgements

The authors thank all Lab LR11ES41 members for assistance. We express our gratitude to Pr. Messaoud Mars (Higher Institute of Agronomy of Chott-Mariem/Laboratory LR02AGR21) for plant material identification and supply. We express our sincere gratitude to Pr. Mohamed Banni (Higher Institute of Biotechnology of Monastir/Laboratory LR02AGR21) for valuable assistance in qRT-PCR analysis and useful discussions.

Funding

The Ministry of Higher Education and Scientific Research provided financial support for this research (Tunisia). The study’s design, data collection, analysis, and interpretation, as well as the writing of the publication, were all done independently from the funder.

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Contributions

DB designed and directed the study. NK performed the in silico analyses, curated and interpreted the data and wrote the manuscript under the guidance of DB. JH assisted NK in data curation and discussion. IB, RM and SG conducted qRT-PCR analysis. KC coordinated and supervised the molecular analyses. All authors have read and approved the final manuscript.

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Correspondence to Dhia Bouktila.

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Handling Editor: Nicola Busatto.

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Supplementary file1 (DOCX 14 KB)

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Supplementary file2 Supplementary file S2. Basic information of WRKY family genes from Ficus carica and Morus notabilis used in this study and annotation of three Ficus carica nonregular WRKY proteins excluded from analyses. (XLS 84 KB)

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Supplementary file3 Supplementary file S3. Results of Domains Database (CDD) and Pfam 32.0, showing conserved domains associated with the WRKY in 49 studied WRKY family proteins from Ficus carica. (XLS 55 KB)

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Supplementary file4 Supplementary file S4. Sequence logos, metrics and distribution graph of the conserved motifs in Ficus carica WRKY proteins. (XLS 228 KB)

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Kmeli, N., Bettaieb, I., Hamdi, J. et al. Genome-Level Investigation of WRKY Transcription Factors and Their Potential Roles in Fruit Peel Ripening and Coloration in the Common Fig (Ficus carica L.). J Plant Growth Regul (2023). https://doi.org/10.1007/s00344-023-11151-4

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  • DOI: https://doi.org/10.1007/s00344-023-11151-4

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