Sulfide as a signaling molecule in autophagy

Hydrogen sulfide is already recognized as an important signaling molecule in mammalian systems, and emerging data suggest that H(2)S is a signaling molecule just as important as nitric oxide (NO) and H(2)O(2) in plants. Although sulfide is generated in chloroplasts and mitochondria, it is present predominantly in the charged HS(-) form due to the basic pH inside both organelles, thus requiring an active transporter, which is yet to be identified, to be released. In Arabidopsis, we found that the cytosolic L-cysteine desulfhydrase DES1 is involved in the degradation of cysteine, and therefore responsible for the generation of H(2)S in this cellular compartment. DES1 deficiency leads to the induction of autophagy. Moreover, we have demonstrated that sulfide in particular exerts a general effect on autophagy through negative regulation, in a way unrelated to nutrient deficiency. The mechanisms of H(2)S action and its molecular targets are largely unknown, although in animal systems, protein S-sulfhydration has been proposed as a mechanism for sulfide-mediated signaling.