SpWRKY6 acts as a positive regulator during tomato resistance to Phytophthora infestans infection

WRKY transcription factors have been widely known to play key regulatory roles in plant disease resistance. In our previous study, characteristics of SpWRKY6 and its role in response to biotic and abiotic stress was studied. To further investigate the function of SpWRKY6 in tomato resistance to Phytophthora infestans (P. infestans), we studied the effects of loss and gain of function of SpWRKY6. Inhibition of SpWRKY6 mRNA accumulation in tomato leaves, using virus-induced gene silencing (VIGS), greatly reduced SpWRKY6 mRNA levels, and compromised tomato resistance to P. infestans. In contrast, overexpressing- SpWRKY6 tomato plants showed enhanced resistance to P. infestans, accompanied by decreased number of necrotic cells, lesion sizes and disease index. Furthermore, after P. infestans infection, the expression levels of pathogenesis related (PR) genes in transgenic tomato plants overexpressed SpWRKY6 were significantly higher than those in wild type plants, while the number of necrotic cells and the reactive oxygen species (ROS) accumulation were fewer and lower. Taken together, these results indicating that SpWRKY6 acts as a positive regulator of tomato resistance to P. infestans infection through regulating the ROS level and the expression level of PR genes along with alleviating cell membrane injury.