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.

Genome-wide identification and molecular characterization of Citrusunshiu WRKY transcription factors in Satsuma mandarin: clues for putative involvement in cell growth, fruit ripening, and stress response

“…Regarding the members of the CiuWRKY family, we have updated our previous results obtained by Ayadi et al (2016), who identified 51, 48, and only one WRKY TF in Citrus sinensis, C. clementina, and Citrus unshiu, respectively. On the other hand, da Silva et al (2017) found 77 WRKY genes from the Citrus sinensis genome, most of them classified in group I (36 CitsWRKYs), group II (35 CitsWRKYs), and group III (6 CitsWRKYs).…”

“…For example, AtWRKY50 and AtWRKY51 are associated with the mechanism of repression between SA and JA (Gao et al, 2011). Also, CsWRKY41 and CsWRKY31 were both expressed in fruits, flowers, and leaves (Ayadi et al, 2016). Interestingly, CiuWRKY1, CcWRKY62, and CsWRKY42 genes are highly similar.…”

“…The identity between CiuWRKY1 and Cs4g05760 was 99% (query cover: 94%, E-value: 4E -114 ) at the amino acid sequence level. Also, the comparison between the peptide sequence deduced from the nucleotide sequence of the CiuWRKY1 gene and the complete protein sequences of Citrus present in different DB (Ayadi et al, 2016) showed that CiuWRKY1 is strongly similar (99%, E-value: 4E -114 ) to CcWRKY62 (Phytozome db: clementine 0.9_024219m) and CsWRKY42 Figure 1. Alignment of the WRKY protein domains from Citrus unshiu by T-COFFEE.…”

“…The WRKY family was represented by 72 members in Arabidopsis (Eulgem et al, 2000), 102 in rice (Ross et al, 2007), 97 in Oryza nivara (Xu et al, 2016), 55 in Cucumis sativus (Ling et al, 2011), 54 in mulberry (Baranwal et al, 2016), 95 in carrot (Li MY et al, 2016), 112 in Gossypium raimondii, and 109 in Gossypium arboretum (Ding et al, 2015). In the genus Citrus, 100 putative WRKYs have been identified: 51 in Citrus sinensis, 48 in C. clementina, and one in Citrus unshiu (Ayadi et al, 2016).…”

In silico genome-wide identification and phylogenetic analysis of the WRKY transcription factor family in sweet orange (Citrus sinensis)

“…In this study, 77 WRKY genes were identified in the C. sinensis genome, 26 genes more than Ayadi et al (2016) (51 genes WRKY). The number of WRKY genes identified in sweet orange was similar to that in A. thaliana (72), higher than that in V. vinifera (59), and lower than that in O. sativa (96), Zea mays (119) and Populus trichocarpa (104).…”