A WRKY Transcription Factor CbWRKY27 Negatively Regulates Salt Tolerance in Catalpa bungei

Catalpa bungei is an economically important tree with high-quality wood, which is highly ornamentally valuable in China. Salinity is one of the major constraints restricting the growth of the C. bungei. However, the molecular mechanism underlying the salt stress response remains unknown in C. bungei. In our previous study, a novel WRKY transcription factor gene CbWRKY27 was isolated using association mapping based on the transcriptome database of Catalpa Yuqiu1. In this study, CbWRKY27 was found to function as a transcriptional activator in the nucleus. The transcription of CbWRKY27 was inhibited under salt stress and reactive oxygen species (ROS) but was induced after abscisic acid (ABA) treatment. CbWRKY27-overexpression plants showed decreased tolerance to salt stress compared to wild type while enhancing sensitivity to ABA-regulated lateral root length. Quantitative real-time PCR (qPCR) studies showed that the transcript levels of the ABA biosynthesis gene (NCED3), signaling genes (ABI3 and ABI5), and responsive genes (RD29B and RD22) were greatly increased in CbWRKY27-overexpression plants under salt stress. Under salt treatment, CbWRKY27-overexpression plants disturbed ROS homeostasis by repressing antioxidant enzymes and enhancing the production of O-2(-) and H2O2 through down-regulation of ROS-scavenging-related genes (APX, SOD, and PER57). In summary, these results indicate that CbWRKY27 negatively regulates salt tolerance in C. bungei.