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Cold plasma technology offers new opportunities to the decontamination and preservation of fruits and vegetables. In the present research, strawberries were cut into four wedges and then treated with dielectric barrier discharge plasma at 45 kV for 1 min and stored for 1 week (4 °C). Metabolomic analysis suggested that plasma treatment improved the biosynthesis of the metabolites in the "flavones and flavonol biosynthesis" pathway and "biosynthesis of phenylpropanoids" pathway in fresh-cut strawberries. Physiological assay demonstrated that plasma treatment maintained the texture properties and inhibited microbial growth of fresh-cut strawberries. In addition, plasma treatment also promoted the accumulation of total phenolics, total flavonoid, and anthocyanin by enhancing the critical enzyme activities and activating related gene expression in phenylpropanoid as well as reactive oxygen species metabolism, which contributed greatly to the enhancement of antioxidant capacity of strawberry wedges. Our investigation provided a new perspective of the effect of plasma treatment on the safety and quality of strawberry wedges and suggested that cold plasma treatment holds promise as an emerging processing technology for improving the quality and antioxidant activity of postharvest fruits and vegetables.

Although heat shock proteins (HSPs), a family of ubiquitous molecular chaperones, are well characterized in heat stress-related responses, their function in plant defense remains largely unclear. Here, we report the role of VvHSP24, a class B HSP from Vitis vinifera, in β-aminobutyric acid (BABA)-induced priming defense against the necrotrophic fungus Botrytis cinerea in grapes. Grapes treated with 10 mmol L–1 BABA exhibited transiently increased transcript levels of VvNPR1 and several SA-inducible genes, including PR1, PR2, and PR5. Additionally, phytoalexins accumulated upon inoculation with the gray mold fungus B. cinerea, which coincided with the action of a priming mode implicated in pathogen-driven resistance. Intriguingly, electrophoretic mobility shift (EMSA), yeast two-hybrid (Y2H) and His pull-down assays demonstrated that the nuclear chaperone VvHSP24 cannot modulate the transcript of PR genes but does directly interact with VvNPR1 in vivo or in vitro. Furthermore, we found that VvHSP24 overexpression enhanced the transcript levels of NPR1 and SA-responsive genes (PR1, PR2, and PR5) and increased the resistance of transgenic Arabidopsis thaliana to B. cinerea compared with wildtype Col-0. An opposite trend between CRISPR mutants of AtHSFB1 (the orthologous gene of VvHSP24 in Arabidopsis) and wildtype plants was observed. Hence, our results suggest that VvHSP24 has a potential role in NPR1-dependent plant resistance to fungal pathogen. BABA-induced priming defense in grapes may require posttranslational modification of the chaperone VvHSP24 to activate VvNPR1 transcript, leading to PR gene expressions and resistance phenotypes.

Virus-induced gene silencing (VIGS) is known as a powerful tool for identifying gene functions during plant growth and development. Tobacco rattle virus (TRV) based VIGS has been successfully employed in many plants. However, there have been few reports that VIGS can be used to study the function of gene at fruit level, especially the genes without visible silencing phenotype. Here we used miniature tomato cultivar Micro-Tom (Solanum lycopersicum L.) as material to silence phytoene desaturase (SlPDS) and SlARG2, an important gene encoding arginase in arginine metabolism, separately or simultaneously with TRV agroinoculated by sprout vacuum-infiltration to test the utility of concurrently silencing two genes. When SlPDS and SlARG2 were co-silenced in the same tissue at the same time, there are no compromises in silencing efficiency and silencing efficacy compared with SlPDS or SlARG2 silenced separately. Moreover, the silence of SlPDS and SlARG2 with TRV agroinoculated by sprout vacuum-infiltration occurred at the early stage of tomato plant, and the silence can extend to full red stage of fruit. Therefore, our results provide a means for functional analysis of genes, particularly the genes with no obvious visible phenotype after silencing, involved in all of the metabolic networks during fruit development and ripening.

The effects of l-arginine (Arg, 1 mM) and/or methyl salicylate (MeSA, 0.05 mM) treatment on gray mold caused by Botrytis cinerea in tomato fruit were studied. Results indicated that Arg or MeSA alleviated the incidence and severity of fruit disease caused by B. cinerea, and that both Arg and MeSA (Arg + MeSA) further inhibited the development of fruit decay. Treatment with Arg + MeSA not only enhanced the activities of superoxide dismutase, catalase, and peroxidase but also promoted the expression levels of pathogenesis-related protein 1 gene and the activities of defense-related enzymes of phenylalanine ammonia-lyase, polyphenol oxidase, β-1,3-glucanase, and chitinase during most of the storage periods, which were associated with lower disease incidence and disease index. In addition, the combined treatment elevated the levels of total phenolics, polyamines, especially putrescine, and nitric oxide. These observations suggest that treatment of fruit with Arg + MeSA is an effective and promising way to alleviate postharvest decays on a commercial scale.

The molecular mechanisms underlying methyl jasmonate (MeJA) primed defense against Rhizopus stolonifer through regulating phenylpropanoid pathway in peaches and the involvement of WRKY transcription factor were investigated. MeJA treatment enhanced the activity of phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL), and promoted the accumulation of total phenolics, total flavonoids and lignin content as well as the main individual phenolic compounds, including chlorogenic acid, neochlorogenic acid and epicatechin. Moreover, transcripts of PpPAL and Pp4CL transcription were substantially and rapidly enhanced upon inoculation with the pathogen in MeJA-treated fruit, indicating that MeJA triggered a priming defense via enhancing phenylpropanoid pathway in peaches. Furthermore, MeJA primed the expression of PpWRKY70, which was identified as a transcription activator of PpPAL and Pp4CL via binding to their W-boxes. Taken together, our results demonstrate that PpWRKY70 is involved in the MeJA-primed defense by activating the phenylpropanoid pathway.

Methyl jasmonate (MeJA) and WRKY transcription factors (TFs) are documented to exert vital defensive functions. Research concerning WRKY TFs together with MeJA-primed defense against Rhizopus stolonifer in peach fruit is still in its infancy. In the present study, the mode of MeJA on inducing resistance against soft rot caused by Rhizopus stolonifer in peaches during the postharvest storage and the involvement of WRKY TFs were investigated, and the results manifested that MeJA at 10 μM significantly reduced disease occurrence and lesion diameter after R. stolonifer infection during 60 h of storage at 20 °C. Moreover, the MeJA treatment promoted the activity of CHI and GLU and elevated the expression levels of PpLOX, PpAOS and PpOPR3. More importantly, the expression of PpCHI, PpGLU, PpPR-like, PpLOX, PpAOS and PpOPR3 were substantially and rapidly elevated in the peach fruit that pretreated with MeJA and inoculated with R.stolonifer, indicating that MeJA stimulated a specific priming defense against Rhizopus rot in peaches. Furthermore, a MeJA-related transcription factor PpWRKY45 was identified and characterized as a nucleus-localized protein that could activate the expression of PpCHI, PpGLU, PpPR-like, PpLOX, PpAOS and PpOPR3 by binding to W-box elements in their promoters. These results indicate that PpWRKY45 is involved in MeJA-primed defense against R. stolonifer by activating JA biosynthetic and PR genes of peach fruit.

The physiological role of arginase in nitrogen remobilization processes from protein degradation during seed germination has well been described in several species. However, very little is known about its possible roles in plant stress responses. Treatment of tomato fruit (Solanum lycopersicum L.) with 0.05 mm methyl jasmonate (MeJA) enhanced transcription levels of arginase genes, especially LeARG2. Chilling injury (CI) of fruit treated with 0.05 mm MeJA for 12 hours was also effectively alleviated, as manifested by decreases in CI index, electrolyte leakage, and malondialdehyde (MDA) content. To investigate the potential role of arginase in MeJA-induced chilling tolerance, fruit were treated with MeJA or the arginase inhibitor Nω-hydroxy-nor-l-arginine (nor-NOHA) combined with MeJA and then stored at 2 °C for 28 days. MeJA-induced arginase activity was strongly inhibited and the reduction of CI by MeJA was nearly abolished by the inhibitor. In addition, MeJA treatment increased the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX); inhibited peroxidase (POD) activities; and promoted proline and polyamines accumulation. These effects were partially counteracted by nor-NOHA; putrescine accumulation, however, was unaffected by the inhibitor. Our results indicate that arginase may be involved in MeJA-induced chilling tolerance, possibly by ameliorating the antioxidant enzyme system of fruit and increasing proline levels.

The priming resistance induced by β-aminobutyric acid (BABA) is a cost-effective strategy to protect postharvest fruit from pathogen infection. The cross-linking underlying E3 ubiquitin ligases, WRKY transcription factors (TFs) and priming defense in peaches, however, remains poorly researched. In the present study, 50 mmol L−1 BABA could induce disease resistance at least by priming peach fruit for an accumulation in H2O2 content following subsequent Rhizopus stolonifer incubation, accompanied by a suppression of the disease incidence and lesion diameter during the incubation at 20 °C. Meanwhile, a WRKY TF (PpWRKY22) and an E3 ubiquitin ligase (PpHOS1) were identified specifically based on analysis and summarization of the differentially expressed genes and proteins in the transcriptome and proteome database of peaches, respectively. Moreover, the putative characterization of PpWRKY22, a Group IIe WRKY TF, and PpHOS1, a RING-type E3 ubiquitin ligase, was expounded. The expression of PpWRKY22 and PpHOS1 was up-regulated in the priming resistance of peach fruit against R. stolonifer, and the two nucleus-localized proteins physically interacted in vivo. Taken together, these findings bring new insights into the functional link between E3 ubiquitin ligases and WRKY TFs in priming resistance, and they enable new perspectives on enhancing the disease resistance of peaches.

Non-thermal cold plasma as a novel method for maintaining safety and inducing phenolic accumulation in fresh-cut pitaya (Hylocereus undatus) fruit and the possible mechanisms were investigated. Results showed that cold plasma treatment (60 kV for 5 min) significantly inhibited the growth of total aerobic bacterial counts, increased the cutting-induced phenolic accumulation and enhanced antioxidant activity in fresh-cut pitaya fruit. Moreover, cold plasma treatment promoted the consumption of main sugars, enhanced the level of energy status, accelerated the generation of reactive oxygen species (ROS) at earlier storage, increased gene expression and activity of crucial enzymes in phenylpropanoid pathway. The present research provides convincing evidence regarding the beneficial effects of cold plasma treatment for inducing phenolic accumulation and enhancing antioxidant activity of fresh-cut pitaya fruit and offers potential opportunity for the processing and preservation of fresh-cut fruits and vegetables.