Abstract
WRKY proteins are a large superfamily of transcription factors that are involved in diverse biological processes including development, as well as biotic and abiotic stress responses in plants. WRKY family proteins have been extensively characterized and analyzed in many plant species, including Arabidopsis, rice, and poplar. However, knowledge on WRKY transcription factors in Santalum album is scarce. Based on S. album genome and transcriptome data, 64 SaWRKY genes were identified in this study. A phylogenetic analysis based on the structures of WRKY protein sequences divided these genes into three major groups (I, II, III) together with WRKY protein sequences from Arabidopsis. Tissue-specific expression patterns showed that 37 SaWRKY genes were expressed in at least one of five tissues (leaves, roots, heartwood, sapwood, or the transition zone), while the remaining four genes weakly expressed in all of these tissues. Analysis of the expression profiles of the 42 SaWRKY genes after callus was initiated by salicylic acid (SA) and methyl jasmonate (MeJA) revealed that 25 and 24 SaWRKY genes, respectively, were significantly induced. The function of SaWRKY1, which was significantly up-regulated by SA and MeJA, was analyzed. SaWRKY1 was localized in the nucleus and its overexpression improved salt tolerance in transgenic Arabidopsis. Our study provides important information to further identify the functions of SaWRKY genes and to understand the roles of SaWRKY family genes involved in the development and in SA- and MeJA-mediated stress responses.
Highlights
Transcription factors (TFs) are proteins that can bind to specific DNA target sites and activate and/or repress transcription of their target genes [1]
WRKY TFs are mainly found in plants, while a few are found in the protist Giardia lamblia and the slime mold Dictyostelium discoideum [2,3]
A C-C-H-H type zinc-finger motif was found in 56 SaWRKY proteins whereas SaWRKY7, 9, 28, 47 and 57 had a C-C-H-C type zinc-finger motif, and other variants of zinc-finger motifs such as C-C-H-T (SaWRKY12, 53), C-C-H-L (SaWRKY25, 51), C-C-H-V (SaWRKY42), C-C-H-Y (SaWRKY45), and C-C-H-S (SaWRKY58), were found (Table 1)
Summary
Transcription factors (TFs) are proteins that can bind to specific DNA target sites and activate and/or repress transcription of their target genes [1]. The WRKY family is characterized by the presence of one or two conserved 60 amino acid WRKY domains (WDs), which include the highly conserved WRKYGQK sequence at its N-terminal end and a zinc-finger-like motif at the C-terminal end [6]. Based on the number of WDs and the pattern of their zinc-finger-like motifs, all members of the WRKY family proteins have been classified into three groups I-III [6,10]. Apart from the WDs and zinc-finger-like motif, domains for transcobalamin (R) proteins coexist with WRKY TFs forming R protein-WRKY genes in monocot genomes such as in switchgrass (Panicum virgatum) [11]
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