Manipulation of Reactive Oxygen Species, Redox and Nitric Oxide Signaling Systems to Activate Plant Innate Immunity for Crop Disease Management

Abstract

Reactive oxygen species (ROS) signaling system involves complex redox processes that require participation by specific signal molecules, such as H2O2 and nitric oxide (NO), and antioxidants, such as tocopherols and riboflavin. ROS signaling network plays a central role in launching the defense. ROS mediates a reiterative signal network underlying systemic induced resistance. ROS appears to interact with various defense signaling systems. ROS induces NO signaling system, salicylic acid (SA) signaling system, ethylene (ET)-mediated signaling system, and jasmonic acid (JA)-dependent signaling system. ROS activates the mitogen-activated protein kinase (MAPK) system. BTH (benzo[1,2,3]thiadiazole-7-carbothioc acid S-methyl ester) is the most successfully developed commercial compound to manipulate ROS signaling system for management of viral, bacterial, and phytoplasma diseases and parasitic plants, which are difficult to be controlled by traditional chemical control methods. BTH has been shown to induce several genes with potential roles in establishing reducing conditions following the oxidative burst induced by it. Thiol-based redox signaling has been suggested to contribute to the activation of a primed state in BTH-treated plants. BTH treatment, which induces redox conditions, activates NPR1 (for non-expresser of PR gene 1) and induces resistance against pathogens. It induced NPR1 mRNA accumulation by several-fold. NPR1 gene is a master regulator of the systemic acquired resistance (SAR) in plants. NPR1 enhances the binding of transcription factors to the promoters of pathogenesis-related (PR) defense genes for activation. Riboflavin is another compound which can be used to manipulate ROS and redox signaling system. It induces H2O2 production. Riboflavin induces priming of defense responses and triggers systemic resistance against pathogens. Vitamin B1 (thiamine) treatment induces systemic acquired resistance in susceptible plants through priming. It is a potential tool to manage pathogens through its action on ROS signaling system. Menadione sodium sulphite (MSB) is a water-soluble addition compound of vitamin K3. It is an effective ROS generator producing superoxide radicals (\( {{\text{O}}_{ 2}}^{ - } \)) and H2O2. MSB treatment induces systemic resistance by activating redox signaling systems. Some herbicides have been shown to act as plant innate immunity system activators. The herbicide lactofen targets protoporphyrinogen oxidase, which in turn causes singlet oxygen generation. Singlet oxygen is involved in triggering ROS-mediated signaling system. Lactofen application provides significant control of fungal and oomycete diseases. Trifluralin, a dinitroaniline herbicide, induces disease resistance against several pathogens by manipulating redox signaling system. Glufosinate ammonium is a nonselective herbicide. It activates ROS-dependent SA signaling system and induces resistance against pathogens. Milsana (Reynoutria sachalinensis formulation) activates ROS-mediated signaling system and is highly effective in controlling powdery mildew diseases in crop plants. β-Aminobutyric Acid (BABA) has been shown to induce disease resistance against various pathogens by triggering ROS production. BABA-induced resistance is mostly based on priming of defense responses rather than on the direct activation of these defense responses. BABA has been shown to prime RbohD gene, which encodes a NADPH oxidase potentially involved in ROS production. Potassium dihydrogen phosphate induces systemic resistance by inducing a rapid generation of superoxide and hydrogen peroxide. Potassium phosphonate triggers ROS signaling system-mediated plant defense responses by rapidly releasing superoxide around the point of infection. Oxycom is a commercially available chemical containing reactive oxygen species. It acts as a plant innate immunity activator. Applications of Oxycom triggers plant immune system downstream of ROS. Several bacterial and fungal biocontrol agents have been shown to induce systemic resistance (ISR) against several plant pathogens in various crop plants. Some of the rhizobacteria activate the plant innate immune system by triggering the ROS signaling system. Pseudomonas fluorescens WCS374 is a potential tool to trigger ROS signaling system and confer resistance against pathogens. Serratia plymuthica ICI270, primes leaves for enhanced attacker-induced accumulation of ROS. It induces accumulation of ROS in leaves and induces systemic resistance. Bacillus mycoides elicits ISR by triggering ROS production. Silicon is another potential tool to enhance defense responses by activating ROS signaling system. Silicon treatment significantly alters the activity of lipoxygenase (LOX), which catalyzes the direct oxygenation of polyunsaturated fatty acids and produces \( {{\text{O}}_{ 2}}^{ - } \). Several silicon-based formulations are available for management of crop diseases. Cysteine-rich receptor-like kinases (CRKs) are connected to redox and ROS signaling. Transgenic plants overexpressing CRK genes show enhanced disease resistance by triggering enhanced ROS production. L-type lectin receptor kinases (LecRKs) have been exploited to develop transgenic disease-resistant plants. These transgenic plants show enhanced production of ROS and trigger defense responses against pathogens. Peroxidases in the cell wall can generate apoplastic H2O2 at neutral to basic pH in the presence of reductants in plant cells. It is possible to generate transgenic plants overexpressing peroxidase gene to overproduce peroxidase resulting in enhanced ROS accumulation. These transgenic plants show enhanced disease resistance. Super oxide dismutase gene has been engineered to activate ROS-mediated immune signaling for disease management. Fungal glucose oxidase gene has been engineered to develop disease-resistant plants. Expression of the fungal glucose oxidase gene leads to elevated production of H2O2 in the transgenic plants resulting in increased resistance. Sodium nitroprusside (SNP) is a NO generator and it effectively controls diseases. NO signaling system can be manipulated by using antisense technology for plant disease management. GSNOR (S-nitroso glutathione reductase) has been exploited using antisense strategy to develop transgenic plants expressing resistance against oomycete and bacterial pathogens. NOS (nitric oxide synthase) has been used to develop transgenic plants. The mammalian NOS isolated from rat brain has been shown to be a potential tool to develop transgenic plants expressing resistance against a wide range of pathogens.