Genome-wide Identification and Expression Analysis of WRKY Transcription Factor Gene Family in Date Palm (Phoenix dactylifera) Reveals its Role in Salt and Drought Stress Responses

Abstract

The WRKY transcription factors are pivotal in regulating several imperious plant growth transcriptional, biological, and metabolic processes. They are integrally involved in various stress responses in plants, significantly biotic and abiotic stresses. WRKY transcription family has been investigated in a large number of plant species, but their characterization and identification are not carried in date palm (Phoenix dactylifera L.) so far. The present study identified 66 non-redundant WRKY-encoding genes that were dispersed unevenly on all 16 chromosomes of the date palm. Based on phylogenetic analysis, PdWRKY genes were classified into three Groups (I, II, and III) while Group II was further divided into five sub-groups i.e., IIa, IIb, IIc, IId, and IIe. Intron-exon analysis exhibited the presence of 2-5 introns within all PdWRKY genes and a variable number of conserved motifs were observed in PdWRKY proteins. Moreover, the signatory WRKY domain was completely conserved, and many other domains were found to be conserved irregularly in PdWRKY proteins. More than fifty cis-acting regulatory elements were identified in upstream promoter regions. The transcriptomic data exhibited the expression patterns and variations of PdWRKY genes in shoot and root tissues stressed under drought and salt conditions. Interestingly, PdWRKY49 and PdWRKY58 showed similar responses in both shoot and root tissues under salt stress while in drought stress almost all PdWRKY genes upregulated in root tissues and showed downregulation in shoot tissues except PdWRKY59 in both tissues respectively. Our findings demonstrated that WRKY proteins frequently act as repressors, along with as activators. Furthermore, the present study indicates that WRKY transcription factors could potentially orchestrate a diverse array of seemingly unrelated functions.