Abstract
Nonhost resistance (NHR) pertains to the most common form of plant resistance against pathogenic microorganisms of other species. Bipolaris maydis is a non-adapted pathogen affecting soybeans, particularly of maize/soybean intercropping systems. However, no experimental evidence has described the immune response of soybeans against B. maydis. To elucidate the molecular mechanism underlying NHR in soybeans, proteomics analysis based on two-dimensional polyacrylamide gel electrophoresis (2-DE) was performed to identify proteins involved in the soybean response to B. maydis. The spread of B. maydis spores across soybean leaves induced NHR throughout the plant, which mobilized almost all organelles and various metabolic processes in response to B. maydis. Some enzymes, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), mitochondrial processing peptidase (MPP), oxygen evolving enhancer (OEE), and nucleoside diphosphate kinase (NDKs), were found to be related to NHR in soybeans. These enzymes have been identified in previous studies, and STRING analysis showed that most of the protein functions related to major metabolic processes were induced as a response to B. maydis, which suggested an array of complex interactions between soybeans and B. maydis. These findings suggest a systematic NHR against non-adapted pathogens in soybeans. This response was characterized by an overlap between metabolic processes and response to stimulus. Several metabolic processes provide the soybean with innate immunity to the non-adapted pathogen, B. maydis. This research investigation on NHR in soybeans may foster a better understanding of plant innate immunity, as well as the interactions between plant and non-adapted pathogens in intercropping systems.
Highlights
Nonhost resistance (NHR) is a plant immune response against major microorganisms that are pathogenic to other plant species [1, 2]
In the maize/soybean intercropping system, maize is susceptible to infection by Bipolaris maydis, whereas soybeans present no detectable symptoms of disease [7]
These proteins were detected in the nucleus, cytoplasm, cell wall, cell membrane, mitochondrion, and Golgi apparatus of root cells in response to a B. maydis challenge on leaves, which might contribute to the multiple NHR responses to non-adapted pathogens
Summary
Nonhost resistance (NHR) is a plant immune response against major microorganisms that are pathogenic to other plant species [1, 2]. A previous microscopy analysis of infected soybeans showed that successful callose deposition and hydrogen peroxide (H2O2) production (S1 Fig) may be the first line of defense against B. maydis growth [7]. Based on these findings, we hypothesized that soybean resistance to B. maydis is established via NHR, which is the most robust and durable forms of plant resistance in nature. Unlike the well-studied host resistance conferred by plant resistance (R) genes, the molecular basis of NHR remains elusive In this present study, the foundation of soybean NHR against B. maydis, a pathogen affecting a remotely related plant species, was characterized at the proteomic level. The results may facilitate further our understanding of NHR in soybean plants
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