The WRKY Transcription Factor Family in Citrus: Valuable and Useful Candidate Genes for Citrus Breeding

Abstract

WRKY transcription factors belong to a large family of plant transcriptional regulators whose members have been reported to be involved in a wide range of biological roles including plant development, adaptation to environmental constraints and response to several diseases. However, little or poor information is available about WRKY’s in Citrus. The recent release of completely assembled genomes sequences of Citrus sinensis and Citrus clementina and the availability of ESTs sequences from other citrus species allowed us to perform a genome survey for Citrus WRKY proteins. In the present study, we identified 100 WRKY members from C. sinensis (51), C. clementina (48) and Citrus unshiu (1), and analyzed their chromosomal distribution, gene structure, gene duplication, syntenic relation and phylogenetic analysis. A phylogenetic tree of 100 Citrus WRKY sequences with their orthologs from Arabidopsis has distinguished seven groups. The CsWRKY genes were distributed across all ten sweet orange chromosomes. A comprehensive approach and an integrative analysis of Citrus WRKY gene expression revealed variable profiles of expression within tissues and stress conditions indicating functional diversification. Thus, candidate Citrus WRKY genes have been proposed as potentially involved in fruit acidification, essential oil biosynthesis and abiotic/biotic stress tolerance. Our results provided essential prerequisites for further WRKY genes cloning and functional analysis with an aim of citrus crop improvement.

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Acknowledgments

Authors would express their sincere gratitude to Sana Louati Elarbi for the proofreading of the paper. This research work was supported by the Ministry of Higher Education and Scientific Research of Tunisia (LR15CBBC02, laboratory grant).

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M. Ayadi and M. Hanana contributed equally to this work.

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Additional File 1

Summary table of the results of various databases according to the species of Citrus (DOCX 17 kb)

Additional File 2

Annotation of complete WRKY gene in Citrus. (A catalog of WRKY proteins in the Citrus) (DOCX 44 kb)

Additional File 3

Phylogenetic tree from amino acid sequences of CsWRKY was depicted by the MEGA V6.06 program with the neighbor-joining method (PDF 14 kb)

Additional File 4

Overview (summary) of experiments used in Plex database (XLSX 11 kb)

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Ayadi, M., Hanana, M., Kharrat, N. et al. The WRKY Transcription Factor Family in Citrus: Valuable and Useful Candidate Genes for Citrus Breeding. Appl Biochem Biotechnol 180, 516–543 (2016). https://doi.org/10.1007/s12010-016-2114-8

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Keywords

  • Citrus
  • WRKY
  • Fruit acidification
  • Essential oil biosynthesis
  • Stress tolerance
  • Zinc finger