Improves Defense Against by Regulating ROS and RNS Metabolism, Redox Balance, and Energy Flow in Cucumber Roots.

Plant survival in the terrestrial ecosystem is influenced by both beneficial and harmful microbes. spp. are a group of filamentous fungi that promote plant growth and resistance to harmful microbes. Previously, we showed that the genus could effectively suppress Fusarium wilt in cucumber. However, the mechanisms that underlie the effects of the genus on plant defense have not been fully substantiated. Two essential metabolic pathways, such as the ascorbate (AsA)-glutathione (GSH) cycle and the oxidative pentose phosphate pathway (OPPP), have been shown to participate in plant tolerance to biotic stressors; nevertheless, the involvement of these pathways in -induced enhanced defense remains elusive. Here, we show that could alleviate oxidative and nitrostative stress by minimizing reactive oxygen species (ROS; hydrogen peroxide and superoxide) and reactive nitrogen species (nitric oxide [NO]) accumulation, respectively, under infection in cucumber roots. The genus enhanced antioxidant potential to counterbalance the overproduced ROS and attenuated the transcript and activity of NO synthase and nitrate reductase. The genus also stimulated -nitrosylated glutathione reductase activity and reduced -nitrosothiol and -nitrosylated glutathione content. Furthermore, the genus enhanced AsA and GSH concentrations and activated their biosynthetic enzymes, γ-GCS and l-galactono-1,4-lactone dehydrogenase. Interestingly, the genus alleviated -inhibited activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, enzymes involved in the OPPP. Such positive regulation of the key enzymes indicates the adequate maintenance of the AsA-GSH pathway and the OPPP, which potentially contributed to improve redox balance, energy flow, and defense response. Our study advances the current knowledge of -induced enhanced defense against in cucumber.