Hydrogen sulfide (H 2 S) could act as a versatile signaling molecule in delaying fruit ripening and senescence. Ethylene (C 2 H 4 ) also plays a key role in climacteric fruit ripening, but little attention has been given to its interaction with H 2 S in modulating fruit ripening and senescence. To study the role of H 2 S treatment on the fruit quality and nutrient metabolism, tomato fruits at white mature stage were treated with ethylene and ethylene plus H 2 S. By comparing to C 2 H 4 treatment, we found that additional H 2 S significantly delayed the color change of tomato fruit, and maintained higher chlorophyll and lower flavonoids during storage. Moreover, H 2 S could inhibit the activity of protease, maintained higher levels of nutritional-related metabolites, such as anthocyanin, starch, soluble protein, ascorbic acid by comparing to C 2 H 4 treatment. Gene expression analysis showed that additional H 2 S 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 H 2 S affected pigments metabolism and the transformation of macromolecular to small molecular metabolites. These results showed that additional H 2 S could maintain the better appearance and nutritional quality than C 2 H 4 treatment alone, and prolong the storage period of post-harvest tomato fruits.

Background: Anthocyanins, which have important biological functions and have a beneficial effect on human health, notably account for pigmentation in purple-fleshed sweet potato tuberous roots. Individual regulatory factors of anthocyanin biosynthesis have been identified; however, the regulatory network of anthocyanin biosynthesis in purple-fleshed sweet potato is unclear. Results: We functionally determined that IbMYB340 cotransformed with IbbHLH2 in tobacco and strawberry receptacles induced anthocyanin accumulation, and the addition of IbNAC56a or IbNAC56b caused increased pigmentation. Furthermore, we confirmed the interaction of IbMYB340 with IbbHLH2 and IbNAC56a or IbNAC56b via yeast two-hybrid and firefly luciferase complementation assays; these proteins could form a MYB340-bHLH2-NAC56a or MYB340-bHLH2-NAC56b transcriptional complex to regulate anthocyanin biosynthesis by binding to the IbANS promoter rather than the IbUFGT promoter. Furthermore, it was found by a transient expression system in tobacco leaves that IbMYB44 could decrease anthocyanin accumulation. Moreover, the interaction of IbMYB44 with IbMYB340 and IbNAC56a or IbNAC56b was verified. This result suggested that IbMYB44 acts as a repressor of anthocyanin in sweet potato. Conclusions: The repressor IbMYB44 affected anthocyanin biosynthesis by competitively inhibiting the IbMYB340-IbbHLH2-IbNAC56a or IbMYB340-IbbHLH2-IbNAC56b regulatory complex formation. Overall, the present study proposed a novel regulatory network whereby several vital TFs play key roles in regulating anthocyanin biosynthesis, and it provides strong insight into the potential mechanism underlying anthocyanin biosynthesis in sweet potato tuberous roots with purple color.

Ethylene (CH) and hydrogen sulfide (HS) play important physiological roles in regulating fruit ripening and senescence. The mechanism of HS in ethylene-induced tomato fruit ripening and senescence is still unknown. Here, we show that exogenous HS reduced the production of superoxide anion (·O), malondialdehyde (MDA), and HO in tomato fruit. Further, additional HS was found to induce the activities of guaiacol peroxidase, catalase, ascorbate peroxidase, and superoxide dismutase compared with CH treatment alone, whereas the activities of lipoxygenase, polyphenol oxidase, and phenylalanine ammonia lyase were adversely affected. Moreover, the expression of the antioxidant-encoding genes SlAPX2, SlCAT1, SlPOD12, and SlCuZnSOD was generally up-regulated with CH-HS cotreatment, compared with their expression after ethylene treatment. Thus, the present results suggest that exogenous HS acts as a fruit-ripening regulator by antagonizing the effect of ethylene, thereby providing a potential application for HS in the postharvest storage of fruit.

BACKGROUND Sweet potato is susceptible to chilling injury during low‐temperature storage. To explore the correlation between chilling injury and reactive oxygen species (ROS) metabolism, the content of ROS and the activities and gene expression of antioxidant enzymes were analyzed in the typical storage‐tolerant cultivar Xushu 32 and storage‐sensitive cultivar Yanshu 25. RESULTS The activities of antioxidant enzymes including ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) were enhanced rapidly in the early period of storage in response to chilling stress. Thereafter, the content of ROS metabolites increased consistently due to gradual decrease in ROS scavenging enzymes. Storage‐tolerant cultivar Xushu 32 had higher antioxidant enzyme activities and gene expressions as well as higher content of antioxidant metabolites and lower content of ROS metabolites compared with storage‐sensitive cultivar Yanshu 25, suggesting that the capacity of ROS scavenging by antioxidant enzymes and antioxidants is highly associated with the tolerance of sweet potato to chilling stress. CONCLUSION These results indicated that the antioxidative system is activated in the storage root of sweet potato and the antioxidative capacity is positively associated with better storage performance in the storage‐tolerant cultivar. © 2019 Society of Chemical Industry

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.