Abstract
Hydrogen sulfide (H2S) has been postulated to be the third gasotransmitter in both animals and plants after nitric oxide (NO) and carbon monoxide (CO). In this review, the physiological roles of H2S in plant growth, development and responses to biotic, and abiotic stresses are summarized. The enzymes which generate H2S are subjected to tight regulation to produce H2S when needed, contributing to delicate responses of H2S to environmental stimuli. H2S occupies a central position in plant sulfur metabolism as it is the link of inorganic sulfur to the first organic sulfur-containing compound cysteine which is the starting point for the synthesis of methionine, coenzyme A, vitamins, etc. In sulfur assimilation, adenosine 5′-phosphosulfate reductase (APR) is the rate-limiting enzyme with the greatest control over the pathway and probably the generation of H2S which is an essential component in this process. APR is an evolutionarily conserved protein among plants, and two conserved domains PAPS_reductase and Thioredoxin are found in APR. Sulfate reduction including the APR-catalyzing step is carried out in chloroplasts. APR, the key enzyme in sulfur assimilation, is mainly regulated at transcription level by transcription factors in response to sulfur availability and environmental stimuli. The cis-acting elements in the promoter region of all the three APR genes in Solanum lycopersicum suggest that multiple factors such as sulfur starvation, cytokinins, CO2, and pathogens may regulate the expression of SlAPRs. In conclusion, as a critical enzyme in regulating sulfur assimilation, APR is probably critical for H2S generation during plants’ response to diverse environmental factors.
Highlights
Over centuries, hydrogen sulfide (H2S) has only been well-known for its unpleasant smell and fierce toxicity
Two domains of PAPS_reductase and Thioredoxin are found in adenosine -phosphosulfate reductase (APR) proteins (Kopriva and Koprivova, 2004)
It has been found that plant APR contains an iron-sulfur cluster that is bound by the N-terminal domain (Kopriva et al, 2001), which is a decisive structure in the sulfate reduction pathway
Summary
Hydrogen sulfide (H2S) has only been well-known for its unpleasant smell and fierce toxicity. Endogenous H2S production has been observed in mammalian cells and shown to control a variety of physiological processes and play important roles in the regulation of the pathogenesis of various diseases (Wang, 2012). Endogenous H2S in plant is generated through the pathway of sulfur assimilation or the decomposition of L-/D-cysteine. Adenosine 5 -phosphosulfate reductase (APR) is a ratelimiting enzyme in sulfur assimilation, which controls the flow of inorganic sulfur into cysteine and probably the endogenous production of H2S. The multifunctional role of H2S in plant growth and development highlights the importance of the regulation of endogenous generation of H2S in adaption to growth stages and in response to biotic and abiotic stresses. Plants reduce and incorporate inorganic sulfur, which is almost entirely available as oxidized sulfate, into cysteine via the reductive sulfate assimilation pathway. APS can be phosphorylated to 3 -phospho-APS (PAPS) by adenosine-5 -phosphosulfae kinase (APSK) to provide
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