Transcriptome-Wide Identification of WRKY Transcription Factors and Their Expression Profiles under Different Types of Biological and Abiotic Stress in Pinus massoniana Lamb

Abstract

<i>Pinus massoniana</i> Lamb, an economically important conifer tree, is widely distributed in China. WRKY transcription factors (TFs) play important roles in plant growth and development, biological and abiotic stress. Nevertheless, there is little information about the WRKY genes in <i>P. massoniana</i>. By searching for conserved WRKY motifs in transcriptomic RNA sequencing data for <i>P. massoniana</i>, 31 sequences were identified as WRKY TFs. Then, phylogenetic and conserved motif analyses of the WRKY family in <i>P. massoniana</i>, <i>Pinus taeda</i> and <i>Arabidopsis thaliana</i> were used to classify WRKY genes. The expression patterns of six <i>PmWRKY</i> genes from different groups were determined using real-time quantitative PCR for 2-year-old <i>P. massoniana</i> seedings grown in their natural environment and challenged by phytohormones (salicylic acid, methyl jasmonate, or ethephon), abiotic stress (H₂O₂) and mechanical damage stress. As a result, the 31 <i>PmWRKY</i> genes identified were divided into three major groups and several subgroups based on structural and phylogenetic features. <i>PmWRKY</i> genes are regulated in response to abiotic stress and phytohormone treatment and may participate in signaling to improve plant stress resistance. Some <i>PmWRKY</i> genes behaved as predicted based on their homology with <i>A. thaliana</i> WRKY genes, but others showed divergent behavior. This systematic analysis lays the foundation for further identification of WRKY gene functions to aid further exploration of the functions and regulatory mechanisms of <i>PmWRKY</i> genes in biological and abiotic stress in <i>P. massoniana</i>.