AUTHOR=Dang Fengfeng , Lin Jinhui , Xue Baoping , Chen Yongping , Guan Deyi , Wang Yanfeng , He Shuilin 

TITLE=CaWRKY27 Negatively Regulates H2O2-Mediated Thermotolerance in Pepper (Capsicum annuum)

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01633

DOI=10.3389/fpls.2018.01633

ISSN=1664-462X

ABSTRACT=<p>Heat stress, an important and damaging abiotic stress, regulates numerous WRKY transcription factors, but their roles in heat stress responses remain largely unexplored. Here, we show that pepper (<italic>Capsicum annuum</italic>) CaWRKY27 negatively regulates basal thermotolerance mediated by H<sub>2</sub>O<sub>2</sub> signaling. <italic>CaWRKY27</italic> expression increased during heat stress and persisted during recovery. <italic>CaWRKY27</italic> overexpression impaired basal thermotolerance in tobacco (<italic>Nicotiana tabacum</italic>) and <italic>Arabidopsis thaliana</italic>, <italic>CaWRKY27</italic>-overexpressing plants had a lower survival rate under heat stress, accompanied by decreased expression of multiple thermotolerance-associated genes. Accordingly, silencing of <italic>CaWRKY27</italic> increased basal thermotolerance in pepper plants. Exogenously applied H<sub>2</sub>O<sub>2</sub> induced <italic>CaWRKY27</italic> expression, and <italic>CaWRKY27</italic> overexpression repressed the scavenging of H<sub>2</sub>O<sub>2</sub> in <italic>Arabidopsis</italic>, indicating a positive feedback loop between H<sub>2</sub>O<sub>2</sub> accumulation and <italic>CaWRKY27</italic> expression. Consistent with this, <italic>CaWRKY27</italic> expression was repressed under heat stress in the presence H<sub>2</sub>O<sub>2</sub> scavengers and <italic>CaWRKY27</italic> silencing decreased H<sub>2</sub>O<sub>2</sub> accumulation in pepper leaves. These changes may result from changes in levels of reactive oxygen species (ROS)-scavenging enzymes, since the heat stress-challenged <italic>CaWRKY27</italic>-silenced pepper plants had significantly higher expression of multiple genes encoding ROS-scavenging enzymes, such as <italic>CaCAT1</italic>, <italic>CaAPX1</italic>, <italic>CaAPX2</italic>, <italic>CaCSD2</italic>, and <italic>CaSOD1</italic>. Therefore, CaWRKY27 acts as a downstream negative regulator of H<sub>2</sub>O<sub>2</sub>-mediated heat stress responses, preventing inappropriate responses during heat stress and recovery.</p>