Overlapping sets of transcripts from host and non-host interactions of tomato are expressed early during non-host resistance

Natural immunity present in all the plants against most of the pathogens is called as non-host resistance (NHR). Although NHR is most durable form of resistance, it was less studied compared to other forms of resistance. We compared transcriptional changes in tomato during non-host (Magnaporthe grisea) and compatible (Alternaria alternata f. sp. lycopersici) interactions using Agilent microarray GeneChip containing ~44,000 probe sets. The experiment was designed to understand the early and late responses of tomato leaves inoculated with non-host and compatible pathogens. Microarray data revealed that the expression profiles in the non-host and compatible interactions at 6 h post inoculation (hpi) and 24 hpi largely overlapped indicating that a set of genes are activated during plant-pathogen interaction. However, these genes were expressed much earlier in NHR compared to a compatible interaction. NHR is, therefore, an accelerated and amplified basal defense response. Transcripts involved in energy production (carbohydrate metabolism and photosynthesis) were down-regulated, whereas transcripts associated with catabolic processes (starch and sucrose hydrolysis) were up-regulated in both the interactions at 6 and 24 hpi. We have also identified that the pathway involved in synthesis of volatile compounds like 2-phenylethanol was induced during NHR in tomato. This is the first report of transcriptome profile in tomato during non-host interactions against M. grisea

Apoplastic oxidative defenses during non-host interactions of tomato (Lycopersicon esculentum L.) with Magnaporthe grisea

Rapid production of reactive oxygen species (ROS) at the apoplast is one of the fastest and the earliest active defense responses against pathogen attack in plants. The aim of the study was to investigate the intensity and timing of the ROS formation, lipid peroxidation and activity of antioxidant enzymes as initial responses of tomato (Lycopersicon esculentum L. cv. Money maker) against the non-host pathogen Magnaporthe grisea. Histological observations revealed that non-host resistance of tomato against M. grisea is associated with the deposition of callose and hypersensitive cell death. The concentration of hydrogen peroxide (H₂O₂) and hydroxyl radicals (·OH) increased during early hours of inoculation, i.e., 24 hour post inoculation (hpi) and 12 hpi, respectively. Superoxide radicals (O₂⁻) increased at 48 hpi in M. grisea-challenged tomato leaves. The activity of the antioxidant enzymes like superoxide dismutase and guaiacol peroxidase increased by 72 hpi in M. grisea-challenged leaves. NADH peroxidase activity was higher at 12 hpi in M. grisea-challenged tomato leaves compared to mock-inoculated leaves. The oxidative burst generated during the non-host interactions of tomato with M. grisea appears to be an early first line of defense by the tomato plants mounted against the invading non-host pathogen. Physical barriers like deposition of callose and hypersensitive cell death were induced by ROS like H₂O₂ and ·OH at early hours, followed by an increase in the activity of antioxidant enzymes contributed to non-host resistance of tomato against M. grisea

Warriors at the gate that never sleep: non-host resistance in plants

The native resistance of most plant species against a wide variety of pathogens is known as non-host resistance (NHR), which confers durable protection to plant species. Only a few pathogens or parasites can successfully cause diseases. NHR is polygenic and appears to be linked with basal plant resistance, a form of elicited protection. Sensing of pathogens by plants is brought about through the recognition of invariant pathogen-associated molecular patterns (PAMPs) that trigger downstream defense signaling pathways. Race-specific resistance, (R)-gene mediated resistance, has been extensively studied and reviewed, while our knowledge of NHR has advanced only recently due to the improved access to excellent model systems. The continuum of the cell wall (CW) and the CW–plasma membrane (PM)-cytoskeleton plays a crucial role in perceiving external cues and activating defense signaling cascades during NHR. Based on the type of hypersensitive reaction (HR) triggered, NHR was classified into two types, namely type-I and type-II. Genetic analysis of Arabidopsis mutants has revealed important roles for a number of specific molecules in NHR, including the role of SNARE-complex mediated exocytosis, lipid rafts and vesicle trafficking. As might be expected, R-gene mediated resistance is found to overlap with NHR, but the extent to which the genes/pathways are common between these two forms of disease resistance is unknown. The present review focuses on the various components involved in the known mechanisms of NHR in plants with special reference to the role of CW–PM components