S-nitrosylation in immunity and fertility: a general mechanism conserved in plants and animals
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Post-translational modification is an intracellular process that modifies the properties of proteins to extend the range of protein function without spending energy in de novo peptide synthesis. There are many post-translational modifications, for example, phosphorylation, ubiquitination, and S-nitrosylation. S-Nitrosylation is a post-translational modification which adds nitric oxide (NO) to sulfhydryl groups at cysteine residues to form S-nitrosothiol (SNO), and is required for plant immunity and fertility. Cellular NO changes between a pool of free NO and bound SNO. During pathogen infection, nitrosative stress in plants is mainly controlled by Snitrosothiolglutathione reductase (GSNOR) via the decomposition of GSNO. GSNOR is an alcohol dehydrogenase type 3 (ADH3) which has both GSNOR and formaldehyde dehydrogenase (FDH) activities. The roles of S-nitrosylation in mammals overlap with those in plants. This conservation led us to explore the relationship between S-nitrosylation, immune response, and fertility in Drosophila melanogaster as it might prove to be a good genetic model for further analysis of the role of S-nitrosylation in animals. I have identified fdh as the likely gsnor in D. melanogaster and have knocked this out using an overlapping deficiency technique in order to observe the effect on immunity and fertility. There are two main pathways in the Drosophila innate immune response, the Toll pathway for protecting against gram-positive bacteria and fungi, and the Imd pathway against gram-negative bacteria. I have investigated the effect of removing GSNOR on sensitivity to gramnegative bacteria (Escherichia coli and Erwinia carotovora) by septic and oral infection, and to fungi (Beauveria bassiana). Susceptibility to infection by the gram negative bacteria was similar to wild-type but susceptibility to B. bassiana was increased. This increase in susceptibility correlated with reduced anti-fungal antimicrobial peptide (AMP) production after B. bassiana infection. This suggests that GSNOR might be required for the normal activity of the Toll pathway or novel Toll-independent processes. We also observed that gsnor knockout impairs fertility and development of embryos.