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Ethylene is a key phytohormone that regulates the ripening of climacteric fruits, and methionine is an indirect precursor of ethylene. However, whether methionine synthase plays a role in fruit ripening in Solanum lycopersicum (tomato) is still unknown. In this study, we find that a tomato methionine synthase (named SlMS1), which could be repressed at the transcriptional level by hydrogen sulfide (H2S), acts as a positive regulator for tomato fruit ripening. By a bioinformatics analysis, it is found that SlMS1 and SlMS2 in tomato are highly homologous to methionine synthases in Arabidopsis thaliana. The expression pattern of SlMS1 and SlMS2 is analyzed in tomato, and SlMS1 expression is up-regulated during fruit ripening, suggesting its potential role in regulating fruit ripening. A potential bipartite nuclear localization signal is found in the amino acid sequence of SlMS1; thus, SlMS1 is tagged with GFP and observed in the leaves of Nicotiana benthamiana. Consistently, SlMS1-GFP shows strong nuclear localization and also cytoplasmic localization. The role of SlMS1 in regulating fruit ripening is investigated in tomato fruit by transient silencing (virus-induced gene silencing, VIGS) and transient overexpression. The results show that SlMS1 silencing causes delayed fruit ripening, evidenced by more chlorophyll and less carotenoid accumulation, while SlMS1 overexpression accelerates fruit ripening significantly compared with control. Further investigation shows that SlMS1 overexpression could up-regulate the expression of carotenoid-synthesis-related genes (PSY1, PDS, ZDS), chlorophyll-degradation-related genes (NYC1, PAO, PPH, SGR1), cell-wall-metabolism-related genes (CEL2, EXP, PG, TBG4, XTH5) and ethylene-synthesis-pathway-related genes (ACO1, ACO3, ACS2), while SlMS1 silencing causes the opposite results. The correlation analysis indicates that SlMS1 expression is negatively correlated with chlorophyll content and positively correlated with carotenoid and ripening-related gene expressions. Taken together, our data suggest that SlMS1 is a positive regulator of tomato fruit ripening and a possible target gene for the ripening-delaying effect of H2S. [ABSTRACT FROM AUTHOR]

As a signaling molecule, hydrogen sulfide (H2S) plays an indispensable role in the modulation of ripening and senescence in fruits and vegetables. To explore the role of H2S in regulating metabolism of postharvest tomato, ripening-related physiological parameters, activities of antioxidant enzymes and gene expression were analyzed in H2S-fumigated tomato fruits. These results show that H2S significantly delayed the color transition and softening of tomato fruit, and maintained higher level of flavonoids and lower level of anthocyanin during storage. Besides, H2S could maintain higher level of nutritional-related metabolites, such as reducing sugar, ascorbic acid during postharvest storage. Moreover, H2S decreased the rate of O2− production, inhibited the production of H2O2 and malondialdehyde (MDA), enhanced the activities of antioxidant enzymes including ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POD) in tomato fruits, while reduced the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and lipoxygenase (LOX). Besides, the expression of the antioxidant-encoding genes SlCAT2, SlPOD12 was generally upregulated with H2S fumigation. Principal component analysis (PCA) suggests that H2S induced significant discrepancy mainly to the differences in firmness, anthocyanin, flavonoid and the activity of guaiacol peroxidase (POD), and the correlation analysis further shows that H2S affected pigment metabolism and nutritional quality. In conclusion, H2S could maintain better appearance and nutritional quality, and prolong the storage period of postharvest tomato fruits through activating the antioxidative system. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is a gaseous signaling molecule that plays multiple roles in plant development. However, whether endogenous H2S plays a role in fruit ripening in tomato is still unknown. In this study, we show that the H2S-producing enzyme l-cysteine desulfhydrase SlLCD1 localizes to the nucleus. By constructing mutated forms of SlLCD1, we show that the amino acid residue K24 of SlLCD1 is the key amino acid that determines nuclear localization. Silencing of SlLCD1 by TRV-SlLCD1 accelerated fruit ripening and reduced H2S production compared with the control. A SlLCD1 gene-edited mutant obtained through CRISPR/Cas9 modification displayed a slightly dwarfed phenotype and accelerated fruit ripening. This mutant also showed increased cysteine content and produced less H2S, suggesting a role of SlLCD1 in H2S generation. Chlorophyll degradation and carotenoid accumulation were enhanced in the SlLCD1 mutant. Other ripening-related genes that play roles in chlorophyll degradation, carotenoid biosynthesis, cell wall degradation, ethylene biosynthesis, and the ethylene signaling pathway were enhanced at the transcriptional level in the lcd1 mutant. Total RNA was sequenced from unripe tomato fruit treated with exogenous H2S, and transcriptome analysis showed that ripening-related gene expression was suppressed. Based on the results for a SlLCD1 gene-edited mutant and exogenous H2S application, we propose that the nuclear-localized cysteine desulfhydrase SlLCD1 is required for endogenous H2S generation and participates in the regulation of tomato fruit ripening. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) could act as a versatile signaling molecule in delaying fruit ripening and senescence. Ethylene (C2H4) also plays a key role in climacteric fruit ripening, but little attention has been given to its interaction with H2S in modulating fruit ripening and senescence. To study the role of H2S treatment on the fruit quality and nutrient metabolism, tomato fruits at white mature stage were treated with ethylene and ethylene plus H2S. By comparing to C2H4 treatment, we found that additional H2S significantly delayed the color change of tomato fruit, and maintained higher chlorophyll and lower flavonoids during storage. Moreover, H2S could inhibit the activity of protease, maintained higher levels of nutritional-related metabolites, such as anthocyanin, starch, soluble protein, ascorbic acid by comparing to C2H4 treatment. Gene expression analysis showed that additional H2S attenuated the expression of beta-amylase encoding gene BAM3 , UDP-glycosyltransferase encoding genes, ethylene-responsive transcription factor ERF003 and DOF22. Furthermore, principal component analysis suggested that starch, titratable acids, and ascorbic acid were important factors for affecting the tomato storage quality, and the correlation analysis further showed that H2S affected pigments metabolism and the transformation of macromolecular to small molecular metabolites. These results showed that additional H2S could maintain the better appearance and nutritional quality than C2H4 treatment alone, and prolong the storage period of post-harvest tomato fruits. [ABSTRACT FROM AUTHOR]

Accumulating evidence shows that hydrogen sulfide (H2S) acts as a multifunctional signaling molecule in plants, whereas the interaction between H2S and ethylene is still unclear. In the present study we investigated the role of H2S in ethylene-promoted banana ripening and senescence by the application of ethylene released from 1.0 g·L−1 ethephon solution or H2S with 1 mM sodium hydrosulfide (NaHS) as the donor or in combination. Fumigation with ethylene was found to accelerate banana ripening and H2S treatment effectively alleviated ethylene-induced banana peel yellowing and fruit softening in parallel with decreased activity of polygalacturonase (PG). Ethylene+H2S treatment also delayed the decreases in chlorophyll and total phenolics, and increased the accumulation of flavonoid, whereas decreased the contents of carotenoid, soluble protein in banana peel and reducing sugar in pulp compared with ethylene treatment alone. Besides, ethylene+H2S treatment suppressed the accumulation of superoxide radicals (·O2−), hydrogen peroxide (H2O2) and malondialdehyde (MDA) which accumulated highly in ethylene-treated banana peels. Furthermore H2S enhanced total antioxidant capacity in ethylene-treated banana peels with the 2,2’-azobis(3-ethylbenz-thiazoline-6-sulfonic acid (ABTS) assay. The result of quantitative real-time PCR showed that the combined treatment of ethylene with H2S down-regulated the expression of ethylene synthesis genes MaACS1, MaACS2 and MaACO1 and pectate lyase MaPL compared with ethylene treatment, while the expression of ethylene receptor genes MaETR, MaERS1 and MaERS2 was enhanced in combination treatment compared with ethylene alone. In all, it can be concluded that H2S alleviates banana fruit ripening and senescence by antagonizing the effect of ethylene through reduction of oxidative stress and inhibition of ethylene signaling pathway. [ABSTRACT FROM AUTHOR]