WRKY transcription factors identified in the transcriptome of Citrus latifolia Tan. and their expression in response to Huanglongbing disease

Huanglongbing (HLB) is the most devastating disease of citrus. Although no citrus species are known to be immune to HLB, some (e.g., Persian lime [Citrus latifolia]) have a high level of tolerance. Differentially expressed genes in the WRKY transcription factor (TF) family have been identified in another tolerant citrus, suggesting an association with such tolerance. Therefore, here we searched for the conserved WRKY domain of WRKY family members in the transcriptome of C. latifolia infected with HLB, characterized the identified ClWRKY genes, and determined which were differentially expressed in leaves with HLB symptoms; 177 transcripts with the WRKY domain were identified, and 32 ClWRKY genes were characterized for conserved motifs, gene ontology, and coexpression networks among the 32 ClWRKY genes. These genes were thus shown to be involved in response to external stimuli and biotic and abiotic stresses. Four differentially expressed ClWRKY genes (ClWRKY20, 23, 47, and 65) were identified in the transcriptome and validated by qRT-PCR. The possible roles of these genes in the tolerance of C. latifolia to HLB are discussed based on the function of homologs of these genes in other plant species. These WRKY genes could contribute to the genetic improvement of susceptible citrus to manage HLB.