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

WRKY transcription factors (TFs) play important roles in several biological processes, especially in defense against different biotic and abiotic stresses.An extensive in silico characterization of the CitsWRKY gene family was performed.In this study, 77 WRKY genes from the Citrus sinensis genome were identified.Based on sequence alignment and phylogenetic analysis, these 77 proteins were classified into three main groups, with most WRKY proteins placed in group I (36 CitsWRKY), group II (35 CitsWRKY), and group III (6 CitsWRKY).Analysis of conserved motifs showed that most identified CitsWRKY proteins carry a conserved WRKY domain.Structural analysis of the genes showed that the number of introns in CitsWRKY genes varied from zero to five.CitsWRKY genes were found to be randomly distributed on all nine chromosomes.The expansion of this gene family may have resulted from 14 tandem and five segmental duplication events.Evaluation of synteny events suggested that some WRKY genes emerged before the divergence of C. sinensis and Arabidopsis.Expression analysis demonstrated that these genes frequently occur in developing tissues such as fruit, flowers, ovaries, meristem, and phloem (65%, 66%, and 85% in groups I, II , and III, respectively), and are stimulated by biotic or abiotic stresses (15%, 16%, and 10% in groups I, II, and III, respectively).The characterization and analysis of these genes will aid in the selection of candidate genes for future functional analyses of the WRKY family in citrus, which will expand our understanding of genetic determinants of stress tolerance.