The Role of Hydrogen Sulfide in Plant Roots during Development and in Response to Abiotic Stress

Unveiling genomic features linked to traits of plant growth-promoting bacterial communities from sugarcane

Microorganisms are ubiquitous, and those inhabiting plants have been the subject of several studies. Plant-associated bacteria exhibit various biological mechanisms that enable them to colonize host plants and, in some cases, enhance their fitness. In this study, we describe the genomic features predicted to be associated with plant growth-promoting traits in six bacterial communities isolated from sugarcane. The use of highly accurate single-molecule real-time sequencing technology for metagenomic samples from these bacterial communities allowed us to recover 17 genomes. The taxonomic assignments for the binned genomes were performed, revealing taxa distributed across three main phyla: Bacillota, Bacteroidota, and Pseudomonadota, with the latter being the most representative. Subsequently, we functionally annotated the metagenome-assembled genomes (MAGs) to characterize their metabolic pathways related to plant growth-promoting traits. Our study successfully identified the enrichment of important functions related to phosphate and potassium acquisition, modulation of phytohormones, and mechanisms for coping with abiotic stress. These findings could be linked to the robust colonization of these sugarcane endophytes.

Expanding roles of cross-talk between hydrogen sulfide and nitric oxide under abiotic stress in plants

Abiotic stress such as salt, heavy metals, drought, temperature, and others can affect plants from seed germination to seedling growth to reproductive maturity. Abiotic stress increases reactive oxygen species and lowers antioxidant enzymes in plants resulted the plant tolerance ability against stress conditions decrease. Hydrogen sulfide (H2S) and nitric oxide (NO) are important gasotransmitters involved in seed germination, photosynthesis, growth and development, metabolism, different physiological processes and functions in plants. In plants, various enzymes are responsible for the biosynthesis of both H2S and NO via both enzymatic and non-enzymatic pathways. They also mediate post-translation modification, such as persulfidation, and nitrosylation, which are protective mechanisms against oxidative damage. They also regulate some cellular signalling pathways in response to various abiotic stress. H2S and NO also stimulate biochemical reactions in plants, including cytosolic osmoprotectant accumulation, reactive oxygen species regulation, antioxidant system activation, K+ uptake, and Na+ cell extrusion or vacuolar compartmentation. In this review, we summarize how H2S and NO interact with each other, the function of both H2S and NO, the mechanism of biosynthesis, and post-translational modification under different abiotic stress. Our main emphasis was to find the cross-talk between NO and H2S and how they regulate genes in plants under abiotic stress.

The role of exogenous hydrogen sulfide in mitigating cadmium toxicity in plants: A comprehensive meta-analysis

Reducing the accumulation of cadmium (Cd) and mitigating its toxicity are pivotal strategies for addressing Cd pollution's threats to agriculture and human health. Hydrogen sulfide (H2S) serves as a signaling molecule, playing a crucial role in plant stress defense mechanisms. Nevertheless, a comprehensive assessment of the impact of exogenous H2S on plant growth, antioxidant properties, and gene expression under Cd stress remains lacking. In this meta-analysis, we synthesized 575 observations from 27 articles, revealing that exogenous H2S significantly alleviates Cd-induced growth inhibition in plants. Specifically, it enhances root length (by 8.71%), plant height (by 15.67%), fresh weight (by 15.15%), dry weight (by 22.54%), and chlorophyll content (by 27.99%) under Cd stress conditions. H2S boosts antioxidant enzyme activity, particularly catalase (CAT), by 39.51%, thereby reducing Cd-induced reactive oxygen species (ROS) accumulation. Moreover, it impedes Cd translocation from roots to shoots, resulting in a substantial 40.19% reduction in stem Cd content. Additionally, H2S influences gene expression in pathways associated with antioxidant enzymes, metal transport, heavy metal tolerance, H2S biosynthesis, and energy metabolism. However, the efficacy of exogenous H2S in alleviating Cd toxicity varies depending on factors such as plant species, concentration of the H2S donor sodium hydrosulfide (NaHS), application method, and cultivation techniques. Notably, NaHS concentrations exceeding 200 μM may adversely affect plants. Overall, our study underscores the role of exogenous H2S in mitigating Cd toxicity and elucidates its mechanism, providing insights for utilizing H2S to combat Cd pollution in agriculture.

Effect of hydrogen sulfide (H2S) on the growth and development of tobacco seedlings in absence of stress

BACKGROUND

Hydrogen sulfide (H2S) is a novel signaling molecule involved in the growth and development of plants and their response to stress. However, the involvement of H2S in promoting the growth and development of tobacco plants is still unclear.

RESULTS

In this study, we explored the effect of pre-soaking or irrigating the roots of tobacco plants with 0.0, 2.0, 4.0, 6.0, and 8.0 mM of sodium hydrosulfide (NaHS) on endogenous H2S production, antioxidant enzymatic and cysteine desulfhydrase activities, seed germination, agronomic traits, photosynthetic pigments contents, and root vigor. The results revealed that exogenous NaHS treatment could significantly promote endogenous H2S production by inducing gene expression of D/L-CD and the activities of D/L-CD enzymes. Additionally, a significant increase in the agronomic traits and the contents of photosynthetic pigments, and no significant difference in carotenoid content among tobacco plants treated with 0.0 to 8.0 mM of NaHS was observed. Additionally, a significant increase in the germination speed, dry weight, and vigor of tobacco seeds, whereas no significant effect on the percentage of seed germination was observed on NaHS treatment. Furthermore, NaHS treatment could significantly increase the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes, which reduces damage due to oxidative stress by maintaining reactive oxygen species homeostasis.

CONCLUSIONS

These results would aid in enhancing our understanding of the involvement of H2S, a novel signaling molecule to promote the growth and development of tobacco plants.

Effect of hydrogen sulfide on cabbage photosynthesis under black rot stress

Hydrogen sulfide (H2S), as a potential gaseous signaling molecule, is involved in mediating biotic and abiotic stress in plants. Currently, there are no studies investigating the mechanism by which H2S improves photosynthesis under black rot (BR) stress caused by Xanthomonas campestris pv. Campestris (Xcc). In this study, we investigated the effect of exogenous H2S on Xcc induced photosynthetic impairment in cabbage seedlings. BR has an inhibitory effect on the photosynthetic ability of cabbage seedlings. Xcc infection can significantly reduce the chlorophyll content, photosynthetic characteristics, chlorophyll fluorescence, Calvin cycle related enzyme activity and gene expression in cabbage leaves. The use of H2S can alleviate this inhibitory effect, reduce chlorophyll decomposition, improve gas exchange, enhance the activity of Calvin cycle related enzymes, and increase the expression of related genes. Transcriptome analysis showed that all differential genes related to photosynthesis were up regulated under H2S treatment compared to normal inoculation. Therefore, spraying exogenous H2S can improve the photosynthetic capacity of cabbage seedlings, reduce Xcc induced photoinhibition, and improve plant resistance.

Repurposing Salicylamides to Combat Phytopathogenic Bacteria and Induce Plant Defense Responses

Based on the research strategy of "drug repurposing", a series of derivatives and marketed drugs that containing salicylic acid skeleton were tested for their antibacterial activities against phytopathogens. Salicylic acid can not only regulate some important growth metabolism of plants, but also induce plant disease resistance. The bioassay results showed that the salicylamides exhibited excellent antibacterial activity. Especially, oxyclozanide showed the best antibacterial effect against Xanthomonas oryzae, Xanthomonas axonopodis pv. citri and Pectobacterium atroseptica with MICs of 0.78, 3.12 and 12.5 μg.mL-1, respectively. In vivo experiments with rice bacterial leaf blight had further demonstrated that oxyclozanide exhibited stronger antibacterial activity than the commercial bactericide, thiodiazole copper. Oxyclozanide could induce plant defense responses through the determination of salicylic acid content and the activities of defense-related enzymes including CAT, POD, and SOD in rice. The preliminarily antibacterial mechanism study indicated that oxyclozanide exhibited the antibacterial activity by disrupting cell integrity and reducing bacterial pathogenicity. Additionally, oxyclozanide could induce plant defense responses through the determination of salicylic acid content.

Exploring the potential role of hydrogen sulfide and jasmonic acid in plants during heavy metal stress

In plants, hydrogen sulfide (H2S) is mainly considered as a gaseous transmitter or signaling molecule that has long been recognized as an essential component of numerous plant cellular and physiological processes. Several subcellular compartments in plants use both enzymatic and non-enzymatic mechanisms to generate H2S. Under normal and stress full conditions exogenous administration of H2S supports a variety of plant developmental processes, including growth and germination, senescence, defense, maturation and antioxidant machinery in plants. Due to their gaseous nature, they are efficiently disseminated to various areas of the cell to balance antioxidant pools and supply sulphur to the cells. Numerous studies have also been reported regarding H2S ability to reduce heavy metal toxicity when combined with other signaling molecules like nitric oxide (NO), abscisic acid (ABA), calcium ion (Ca2+), hydrogen peroxide (H2O2), salicylic acid (SA), ethylene (ETH), jasmonic acid (JA), proline (Pro), and melatonin. The current study focuses on multiple pathways for JA and H2S production as well as their signaling functions in plant cells under varied circumstances, more specifically under heavy metal, which also covers role of H2S and Jasmonic acid during heavy metal stress and interaction of hydrogen sulfide with Jasmonic acid.

Deciphering the role of mechanosensitive channels in plant root biology: perception, signaling, and adaptive responses

MAIN CONCLUSION

Mechanosensitive channels are integral membrane proteins that rapidly translate extrinsic or intrinsic mechanical tensions into biological responses. They can serve as potential candidates for developing smart-resilient crops with efficient root systems. Mechanosensitive (MS) calcium channels are molecular switches for mechanoperception and signal transduction in all living organisms. Although tremendous progress has been made in understanding mechanoperception and signal transduction in bacteria and animals, this remains largely unknown in plants. However, identification and validation of MS channels such as Mid1-complementing activity channels (MCAs), mechanosensitive-like channels (MSLs), and Piezo channels (PIEZO) has been the most significant discovery in plant mechanobiology, providing novel insights into plant mechanoperception. This review summarizes recent advances in root mechanobiology, focusing on MS channels and their related signaling players, such as calcium ions (Ca2+), reactive oxygen species (ROS), and phytohormones. Despite significant advances in understanding the role of Ca2+ signaling in root biology, little is known about the involvement of MS channel-driven Ca2+ and ROS signaling. Additionally, the hotspots connecting the upstream and downstream signaling of MS channels remain unclear. In light of this, we discuss the present knowledge of MS channels in root biology and their role in root developmental and adaptive traits. We also provide a model highlighting upstream (cell wall sensors) and downstream signaling players, viz., Ca2+, ROS, and hormones, connected with MS channels. Furthermore, we highlighted the importance of emerging signaling molecules, such as nitric oxide (NO), hydrogen sulfide (H2S), and neurotransmitters (NTs), and their association with root mechanoperception. Finally, we conclude with future directions and knowledge gaps that warrant further research to decipher the complexity of root mechanosensing.

Transcriptional and post-translational regulation of plant autophagy

In response to changing environmental conditions, plants activate cellular responses to enable them to adapt. One such response is autophagy, in which cellular components, for example proteins and organelles, are delivered to the vacuole for degradation. Autophagy is activated by a wide range of conditions, and the regulatory pathways controlling this activation are now being elucidated. However, key aspects of how these factors may function together to properly modulate autophagy in response to specific internal or external signals are yet to be discovered. In this review we discuss mechanisms for regulation of autophagy in response to environmental stress and disruptions in cell homeostasis. These pathways include post-translational modification of proteins required for autophagy activation and progression, control of protein stability of the autophagy machinery, and transcriptional regulation, resulting in changes in transcription of genes involved in autophagy. In particular, we highlight potential connections between the roles of key regulators and explore gaps in research, the filling of which can further our understanding of the autophagy regulatory network in plants.

Transcriptomic analysis reveals the functions of H2S as a gasotransmitter independently of Cys in Arabidopsis

Numerous studies have revealed the gasotransmitter functions of hydrogen sulfide (H₂S) in various biological processes. However, the involvement of H₂S in sulfur metabolism and/or Cys synthesis makes its role as a signaling molecule ambiguous. The generation of endogenous H₂S in plants is closely related to the metabolism of Cys, which play roles in a variety of signaling pathway occurring in various cellular processes. Here, we found that exogenous H₂S fumigation and Cys treatment modulated the production rate and content of endogenous H₂S and Cys to various degrees. Furthermore, we provided comprehensive transcriptomic analysis to support the gasotransmitter role of H₂S besides as a substrate for Cys synthesis. Comparison of the differentially expressed genes (DEGs) between H₂S and Cys treated seedlings indicated that H₂S fumigation and Cys treatment caused different influences on gene profiles during seedlings development. A total of 261 genes were identified to respond to H₂S fumigation, among which 72 genes were co-regulated by Cys treatment. GO and KEGG enrichment analysis of the 189 genes, H₂S but not Cys regulated DEGs, indicated that these genes mainly involved in plant hormone signal transduction, plant-pathogen interaction, phenylpropanoid biosynthesis, and MAPK signaling pathway. Most of these genes encoded proteins having DNA binding and transcription factor activities that play roles in a variety of plant developmental and environmental responses. Many stress-responsive genes and some Ca²⁺ signal associated genes were also included. Consequently, H₂S regulated gene expression through its role as a gasotransmitter, rather than just as a substrate for Cys biogenesis, and these 189 genes were far more likely to function in H₂S signal transduction independently of Cys. Our data will provide insights for revealing and enriching H₂S signaling networks.

Melatonin involves hydrogen sulfide in the regulation of H+-ATPase activity, nitrogen metabolism, and ascorbate-glutathione system under chromium toxicity

Contamination of soils with chromium (Cr) jeopardized agriculture production globally. The current study was planned with the aim to better comprehend how melatonin (Mel) and hydrogen sulfide (H₂S) regulate antioxidant defense system, potassium (K) homeostasis, and nitrogen (N) metabolism in tomato seedlings under Cr toxicity. The data reveal that application of 30 μM Mel to the seedlings treated with 25 μM Cr has a positive effect on H₂S metabolism that resulted in a considerable increase in H₂S. Exogenous Mel improved phytochelatins content and H⁺-ATPase activity with an associated increase in K content as well. Use of tetraethylammonium chloride (K⁺-channel blocker) and sodium orthovanadate (H⁺-ATPase inhibitor) showed that Mel maintained K homeostasis through regulating H⁺-ATPase activity under Cr toxicity. Supplementation of the stressed seedlings with Mel substantially scavenged excess reactive oxygen species (ROS) that maintained ROS homeostasis. Reduced electrolyte leakage and lipid peroxidation were additional signs of Mel's ROS scavenging effects. In addition, Mel also maintained normal functioning of nitrogen (N) metabolism and ascorbate-glutathione (AsA-GSH) system. Improved level of N fulfilled its requirement for various enzymes that have induced resilience during Cr stress. Additionally, the AsA-GSH cycle's proper operation maintained redox equilibrium, which is necessary for the biological system to function normally. Conversely, 1 mM hypotaurine (H₂S scavenger) abolished the Mel-effect and again Cr-induced impairment on the above-mentioned parameters was observed even in presence of Mel. Therefore, based on the observed findings, we concluded that Mel needs endogenous H₂S to alleviate Cr-induced impairments in tomato seedlings.