Abstract
Plant pathogens generally employ superoxide dismutase (SOD) to detoxify host defense reactive oxygen species (ROS), and to scavenge ROS derived from their own metabolism. However, the roles of SODs in an important vascular pathogen, Verticillium dahliae, are unclear. Our previous study has shown that a putative signal-peptide-lacking manganese superoxide dismutase (VdSOD3) is present in the exoproteome of V. dahliae cultured in tissues of host cotton, suggesting that VdSOD3 may be exported out of the fungal cells and contribute to the SOD activity extracellularly. Here, we confirm that the N-terminal of VdSOD3 is not a functional signal peptide by yeast signal trap assay. Despite lacking the signal peptide, the extracellular distribution of VdSOD3 was observed in planta by confocal microscopy during infection. Loss-of-function of VdSOD3 decreased extracellular and intracellular SOD activities of V. dahliae by 58.2% and 17.4%, respectively. Deletion mutant of VdSOD3 had normal growth and conidiation but showed significantly reduced virulence to susceptible hosts of cotton and Nicotiana benthamiana. Our data show that signal-peptide-lacking VdSOD3 is a dual function superoxide dismutase, localizing and functioning intracellularly and extracellularly. Whereas nonessential for viability, VdSOD3 plays a vital role in the virulence of V. dahliae.
Highlights
In the course of infection, besides being challenged by reactive oxygen species (ROS)produced intracellularly as a natural byproduct of pathogen respiration, plant pathogens are confronted with extracellular ROS generated by the host innate immune response [1]
These results indicated that VdSOD3 is likely a signal-peptide-lacking Mn-superoxide dismutase (SOD) exported into the extracellular space unconventionally
Asexpected, expected, expression we found that the total activity in the hyphal extract decreased significantly by we found that the total SOD activity in the hyphal extract decreased significantly by in VdSOD3 deletion mutants compared to that theofwild-type strain, indicating that in VdSOD3 deletion mutants compared to of that the wild-type strain, indicating
Summary
Produced intracellularly as a natural byproduct of pathogen respiration, plant pathogens are confronted with extracellular ROS generated by the host innate immune response [1]. These ROS have the oxidation capacity to damage virtually all organic and many inorganic components of the pathogen, leading to cellular dysfunction and eventually pathogen death [2]. Superoxide dismutases (SODs), the first-line enzymes against superoxide damage [3], are highly conserved metalloenzymes that use a redox-active cofactored metal to catalyze the conversion of superoxide anion to oxygen and hydrogen peroxide; the latter is further removed by catalase and peroxidase enzymes [4]. Mn-SODs contribute to pathogens’ virulence such as Cryptococcus neoformans, Metarhizium robertsii, Candida glabrata and Beauveria bassiana [6]
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