AUTHOR=Jiang Yaoyao , Zheng Weiran , Li Jing , Liu Peng , Zhong Kaili , Jin Peng , Xu Miaoze , Yang Jian , Chen Jianping 

TITLE=NbWRKY40 Positively Regulates the Response of Nicotiana benthamiana to Tomato Mosaic Virus via Salicylic Acid Signaling

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.603518

DOI=10.3389/fpls.2020.603518

ISSN=1664-462X

ABSTRACT=<p>WRKY transcription factors play important roles in plants, including responses to stress; however, our understanding of the function of <italic>WRKY</italic> genes in plant responses to viral infection remains limited. In this study, we investigate the role of <italic>NbWRKY40</italic> in <italic>Nicotiana benthamiana</italic> resistance to tomato mosaic virus (ToMV). <italic>NbWRKY40</italic> is significantly downregulated by ToMV infection, and subcellular localization analysis indicates that NbWRKY40 is targeted to the nucleus. In addition, NbWRKY40 activates W-box-dependent transcription in plants and shows transcriptional activation in yeast cells. Overexpressing <italic>NbWRKY40</italic> (OEWRKY40) inhibits ToMV infection, whereas <italic>NbWRKY40</italic> silencing confers susceptibility. The level of salicylic acid (SA) is significantly higher in OEWRKY40 plants compared with that of wild-type plants. In addition, transcript levels of the SA-biosynthesis gene (<italic>ICS1</italic>) and SA-signaling genes (<italic>PR1b</italic> and <italic>PR2</italic>) are dramatically higher in OEWRKY40 plants than in the control but lower in <italic>NbWRKY40</italic>-silenced plants than in the control. Furthermore, electrophoretic mobility shift assays show that NbWRKY40 can bind the W-box element of <italic>ICS1</italic>. Callose staining reveals that the plasmodesmata is decreased in OEWRKY40 plants but increased in <italic>NbWRKY40</italic>-silenced plants. Exogenous application of SA also reduces viral accumulation in <italic>NbWRKY40</italic>-silenced plants infected with ToMV. RT-qPCR indicates that NbWRKY40 does not affect the replication of ToMV in protoplasts. Collectively, our findings suggest that NbWRKY40 likely regulates anti-ToMV resistance by regulating the expression of SA, resulting in the deposition of callose at the neck of plasmodesmata, which inhibits viral movement.</p>