Identification of a drought- and cold-stress inducible WRKY gene in the cold-hardy Citrus relative Poncirus trifoliata

Abstract WRKY transcription factors (TFs) are involved in regulation of abiotic and biotic stress responsive genes and play a role in abiotic and biotic stress tolerance in plants. Although commercial Citrus species are sensitive to cold and drought stresses, an interfertile Citrus relative, Poncirus trifoliata, is resistant to cold and more drought tolerant than most commercial Citrus cultivars. An expressed sequence tag clone sharing homology with WRKY-type TFs was previously isolated from a cDNA library constructed using two-day cold-acclimated P. trifoliata cv. Rubidoux seedlings. In this study, a full-length sequence of this WRKY gene was cloned and isolated from 2-day cold-acclimated P. trifoliata plants using the rapid amplification of cDNA ends (RACE) method. The full-length PtrWRKY1 cDNA is 1807 bp and encodes a polypeptide of 405 amino acids containing a single WRKY domain with a Cys2His2 motif, which is a signature of WRKY TFs. A homologous open reading frame (ORF) sequence was isolated from Ci...