Methionine elicits H2O2 generation and defense gene expression in grapevine and reduces Plasmopara viticola infection

Methionine (Met) is a nutritionally essential sulfur-containing amino acid (SAA) known for its preponderant role as initiator in protein synthesis. However, other functions for Met in plants are not well described. The implication of this SAA in oxidative stress tolerance has been recently reported, however the mode of action of Met is still poorly understood. Here, we analyzed the elicitor activity of Met in grapevine as well as its effect on Plasmopara viticola resistance. The results show that Met induces hydrogen peroxide (H2O2) generation, a key element in plant defense signaling, and upregulates the expression of a battery of defense-related genes. Transcript levels of these genes were not further modulated by P. viticola inoculation of Met-pretreated plants, suggesting an elicitor role rather than a priming role for Met in grapevine. Met treatment also reduces P. viticola development in grapevine plants grown under glasshouse controlled-conditions. Fungitoxicity assays revealed that Met possesses a moderate antifungal activity compared with cysteine (Cys), another SAA known for its toxic effect to a large spectrum of fungi.

N-terminus regulation of VMAT2 mediates methamphetamine-stimulated efflux

The 20 amino acid (AA) N-terminus of the vesicular monoamine transporter 2 (VMAT2) was examined as a regulator of VMAT2 function. Removal of the first 16 or 19 AAs of the N-terminus resulted in a molecule with reduced ability to sequester [(3)H]-5HT. A glutathione-S-transferase-construct of the N-terminus underwent phosphorylation in the presence of PKC at serines 15 and 18. These putative phosphorylation sites were examined for effects on function. Phospho-mimetic substitution of serines 15 and 18 with aspartate in the full-length VMAT2 resulted in reduced [(3)H]-5HT sequestration and reduced methamphetamine (METH)-stimulated efflux of preloaded [(3)H]-5HT. In contrast, mutation of serines 15 and 18 to alanines maintained intact net substrate sequestration but eliminated METH-stimulated efflux of pre-accumulated [(3)H]-5HT. In summary, these data suggest a model in which the VMAT2 N-terminus regulates monoamine sequestration.