Transcriptome analysis reveals insight into molecular hydrogen-induced cadmium tolerance in alfalfa: the prominent role of sulfur and (homo)glutathione metabolism

Abstract

Background: Hydrogen gas (H 2) is hypothesised to play a role in plants that are coping with stresses by regulating signal transduction and gene expression. Although the beneficial role of H 2 in plant tolerance to cadmium (Cd) has been investigated previously, the corresponding mechanism has not been elucidated. In this report, the transcriptomes of alfalfa seedling roots under Cd and/or hydrogen-rich water (HRW) treatment were first analysed. Then, the sulfur metabolism pathways were focused on and further investigated by pharmacological and genetic approaches. Results: A total of 1968 differentially expressed genes (DEGs) in alfalfa seedling roots under Cd and/or HRW treatment were identified by RNA-Seq. The DEGs were classified into many clusters, including glutathione (GSH) metabolism, oxidative stress, and ATP-binding cassette (ABC) transporters. The results validated by RT-qPCR showed that the levels of relevant genes involved in sulfur metabolism were enhanced by HRW under Cd treatment, especially the genes involved in (homo)glutathione metabolism. Additional experiments carried out with a glutathione synthesis inhibitor and Arabidopsis thaliana cad2-1 mutant plants suggested the prominent role of glutathione in HRW-induced Cd tolerance. These results were in accordance with the effects of HRW on the contents of (homo)glutathione and (homo)phytochelatins and in alleviating oxidative stress under Cd stress. In addition, the HRW-induced alleviation of Cd toxicity might also be caused by a decrease in available Cd in seedling roots, achieved through ABC transportermediated secretion. Conclusions: Taken together, the results of our study indicate that H 2 regulated the expression of genes relevant to sulfur and glutathione metabolism and enhanced glutathione metabolism which resulted in Cd tolerance by activating antioxidation and Cd chelation. These results may help to elucidate the mechanism governing H 2-induced Cd tolerance in alfalfa.

Phytoremediation of Cadmium: Physiological, Biochemical, and Molecular Mechanisms

“…Similarly, analysis of the EDX spectrum in potato exposed to different Cd concentrations indicated that the highest amount of Cd was stored in the mesophilic tissue of leaves by binding to S-rich compounds [230]. A study on alfalfa under Cd stress conditions indicated that Cd tolerance in seedling roots was enhanced by increasing levels of the expression of genes associated with sulfur metabolism, especially genes implicated in GSH and PCs biosynthesis, also ABC transporters [231]. Due to the low pH of vacuoles, Cd-PCs complexes disassociate, and Cd can be stabilized in vacuoles by binding to ligands, including organic acids and probably amino acids [232].…”

Hydrogen Nanobubble Water Delays Petal Senescence and Prolongs the Vase Life of Cut Carnation (Dianthus caryophyllus L.) Flowers

“…Interestingly, the production of H 2 has been observed in plants under the normal or stressed conditions [ 10 , 11 , 12 ], although its detailed synthetic pathway (s) are not fully elucidated. Further studies have revealed that H 2 played an important role in defense responses of plants to abiotic stresses [ 13 , 14 , 15 ], plant growth [ 16 ], and secondary metabolism [ 17 ]. H 2 was beneficial to postharvest preservation of fruits (kiwifruit [ 18 , 19 ] and tomato [ 20 ]) and cut flowers (rose [ 21 ], lily [ 22 ], and Lisianthus [ 23 ]).…”

Downstream Signalling from Molecular Hydrogen

“…H 2 fits into this suite of reactive signalling molecules and was shown to increase the fitness of plants [24]. Suitable examples of recent papers on H 2 effects on plants include mitigation of salinity effects in barley [25] and Arabidopsis [26], and increased tolerance to cadmium in alfalfa [27]. However, exactly how H 2 interacts and has an effect is unclear.…”