SpWRKY1 mediates resistance to Phytophthora infestans and tolerance to salt and drought stress by modulating reactive oxygen species homeostasis and expression of defense-related genes in tomato

Abstract

WRKY transcription factors play essential roles in diverse signaling pathways related to plant defense responses. However, research focusing on the WRKY family in tomato is fairly limited. In this work, a pathogen-induced SpWRKY1 gene from the wild tomato Solanum pimpinellifolium L3708 showing that its overexpression in cultivated tomato Solanum lycopersicum cv. Zaofen No. 2 results in markedly increased resistance to Phytophthora infestans than untransformed wild-type plant, mainly demonstrated by less severe cell death, lower reactive oxygen species (ROS) production, malonaldehyde (MDA) content, relative electrolyte leakage (REL) and stomatal conductance; and higher peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia-lyase, chlorophyll content and photosynthetic rate. This resistance was also coupled with enhanced the expression of ROS scavenging-related genes, SA/JA-responsive genes and SA/JA biosynthesis-related genes. This overexpression was accompanied by regulating the expression of an ABA biosynthetic gene, reveals a potentially positive role of SpWRKY1 in ABA-mediated stomatal closure. Furthermore, transgenic tomato also displayed an enhanced tolerance to salt and drought stress by decreasing ROS generation, reducing MDA content and REL, improving POD, SOD and proline content, keeping leaf relative water content, preventing chlorophyll loss, and protecting photosynthetic rate and stomatal conductance, accompanied by not only enhanced expression of some ROS scavenging-related and stress-related genes, but also directly up-regulated the expressions of PR genes in response to salt and drought stress. These findings broaden our knowledge about the functions of SpWRKY1 in diverse signalling pathways and may be useful in improving tomato plants tolerance to biotic and abiotic stress.