Exogenous phytosulfokine α (PSKα) applying delays senescence and relief decay in strawberry fruits during cold storage by sufficient intracellular ATP and NADPH availability

Peptide hormones in plants

Peptide hormones are defined as small secreted polypeptide-based intercellular communication signal molecules. Such peptide hormones are encoded by nuclear genes, and often go through proteolytic processing of preproproteins and post-translational modifications. Most peptide hormones are secreted out of the cell to interact with membrane-associated receptors in neighboring cells, and subsequently activate signal transductions, leading to changes in gene expression and cellular responses. Since the discovery of the first plant peptide hormone, systemin, in tomato in 1991, putative peptide hormones have continuously been identified in different plant species, showing their importance in both short- and long-range signal transductions. The roles of peptide hormones are implicated in, but not limited to, processes such as self-incompatibility, pollination, fertilization, embryogenesis, endosperm development, stem cell regulation, plant architecture, tissue differentiation, organogenesis, dehiscence, senescence, plant-pathogen and plant-insect interactions, and stress responses. This article, collectively written by researchers in this field, aims to provide a general overview for the discoveries, functions, chemical natures, transcriptional regulations, and post-translational modifications of peptide hormones in plants. We also updated recent discoveries in receptor kinases underlying the peptide hormone sensing and down-stream signal pathways. Future prospective and challenges will also be discussed at the end of the article.

Phytomelatonin: From Intracellular Signaling to Global Horticulture Market

Melatonin (N-acetyl-5-methoxytryptamine), a well-known mammalian hormone, has been having a great relevance in the Plant World in recent years. Many of its physiological actions in plants are leading to possible features of agronomic interest, especially those related to improvements in tolerance to stressors and in the postharvest life of fruits and vegetables. Thus, through the exogenous application of melatonin or by modifying the endogenous biosynthesis of phytomelatonin, some change can be made in the functional levels of melatonin in tissues and their responses. Also, acting in the respective phytomelatonin biosynthesis enzymes, regulating the expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin O-methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), and recently the possible action of deacetylases on some intermediates offers promising opportunities for improving fruits and vegetables in postharvest and its marketability. Other regulators/effectors such as different transcription factors, protein kinases, phosphatases, miRNAs, protein-protein interactions, and some gasotransmitters such as nitric oxide or hydrogen sulfide were also considered in an exhaustive vision. Other interesting aspects such as the role of phytomelatonin in autophagic responses, the posttranslational reprogramming by protein-phosphorylation, ubiquitylation, SUMOylation, PARylation, persulfidation, and nitrosylation described in the phytomelatonin-mediated responses were also discussed, including the relationship of phytomelatonin and several plant hormones, for chilling injury and fungal decay alleviating. The current data about the phytomelatonin receptor in plants (CAND2/PMTR1), the effect of UV-B light and cold storage on the postharvest damage are presented and discussed. All this on the focus of a possible new action in the preservation of the quality of fruits and vegetables.

Interplay among photoreceptors determines the strategy of coping with excess light in tomato

This study investigates photoreceptor's role in the adaption of photosynthetic apparatus to high light (HL) intensity by examining the response of tomato wild type (WT) (Solanum lycopersicum L. cv. Moneymaker) and tomato mutants (phyA, phyB1, phyB2, cry1) plants to HL. Our results showed a photoreceptor-dependent effect of HL on the maximum quantum yield of photosystem II (Fv/Fm) with phyB1 exhibiting a decrease, while phyB2 exhibiting an increase in Fv/Fm. HL resulted in an increase in the efficient quantum yield of photosystem II (ΦPSII) and a decrease in the non-photochemical quantum yields (ΦNPQ and ΦN0) solely in phyA. Under HL, phyA showed a significant decrease in the energy-dependent quenching component of NPQ (qE), while phyB2 mutants showed an increase in the state transition (qT) component. Furthermore, ΔΔFv/Fm revealed that PHYB1 compensates for the deficit of PHYA in phyA mutants. PHYA signaling likely emerges as the dominant effector of PHYB1 and PHYB2 signaling within the HL-induced signaling network. In addition, PHYB1 compensates for the role of CRY1 in regulating Fv/Fm in cry1 mutants. Overall, the results of this research provide valuable insights into the unique role of each photoreceptor and their interplay in balancing photon energy and photoprotection under HL condition.

Phytosulfokine promotes fruit ripening and quality via phosphorylation of transcription factor DREB2F in tomato

Phytosulfokine (PSK), a plant peptide hormone with a wide range of biological functions, is recognized by its receptor PHYTOSULFOKINE RECEPTOR 1 (PSKR1). Previous studies have reported that PSK plays important roles in plant growth, development, and stress responses. However, the involvement of PSK in fruit development and quality formation remains largely unknown. Here, using tomato (Solanum lycopersicum) as a research model, we show that exogenous application of PSK promotes the initiation of fruit ripening and quality formation, while these processes are delayed in pskr1 mutant fruits. Transcriptomic profiling revealed that molecular events and metabolic pathways associated with fruit ripening and quality formation are affected in pskr1 mutant lines and transcription factors are involved in PSKR1-mediated ripening. Yeast screening further identified that DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN 2F (DREB2F) interacts with PSKR1. Silencing of DREB2F delayed the initiation of fruit ripening and inhibited the promoting effect of PSK on fruit ripening. Moreover, the interaction between PSKR1 and DREB2F led to phosphorylation of DREB2F. PSK improved the efficiency of DREB2F phosphorylation by PSKR1 at the tyrosine-30 site, and the phosphorylation of this site increased the transcription level of potential target genes related to the ripening process and functioned in promoting fruit ripening and quality formation. These findings shed light on the involvement of PSK and its downstream signaling molecule DREB2F in controlling climacteric fruit ripening, offering insights into the regulatory mechanisms governing ripening processes in fleshy fruits.

Exogenous Phytosulfokine α (PSKα) Alleviates Chilling Injury of Kiwifruit by Regulating Ca2+ and Protein Kinase-Mediated Reactive Oxygen Species Metabolism

Kiwifruit fruit stored at low temperatures are susceptible to chilling injury, leading to rapid softening, which therefore affects storage and marketing. The effect of 150 nM mL-1 of exogenous phytosulfokine α (PSKα) on reactive oxygen species (ROS) metabolism, Ca2+ signaling, and signal-transducing MAPK in kiwifruit, stored at 0 °C for 60 days, was investigated. The results demonstrated that PSKα treatment effectively alleviated chilling injury in kiwifruit, with a 15% reduction in damage compared to the control on day 60. In addition, PSKα enhanced the activities and gene expression levels of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), Ca2+-ATPase, and mitogen-activated protein kinase (MAPK). In contrast, the activities and gene expression levels of NADPH oxidase (NOX) were inhibited, leading to a lower accumulation of O2- and H2O2, which were 47.2% and 42.2% lower than those in the control at the end of storage, respectively. Furthermore, PSKα treatment enhanced the calmodulin (CaM) content of kiwifruit, which was 1.41 times that of the control on day 50. These results indicate that PSKα can mitigate chilling injury and softening of kiwifruit by inhibiting the accumulation of ROS, increasing antioxidant capacity by inducing antioxidant enzymes, activating Ca2+ signaling, and responding to MAPK protein kinase. The present results provide evidence that exogenous PSKα may be taken for a hopeful treatment in alleviating chilling injury and maintaining the quality of kiwifruit.

Effect of postharvest nicotinamide treatment on NAD+ metabolism and redox status in strawberry fruit during storage

The increased activity of PARP enzymes is associated with a deficiency of NAD+, as well as with a loss of NADPH and ATP, and consequent deterioration of the redox state in fruits. In this study, we checked whether treatment with nicotinamide (NAM) would affect PARP-1 expression and NAD+ metabolism in strawberry fruit during storage. For this purpose, strawberry fruits were treated with 10 mM NAM and co-treated with NAM and UV-C, and then stored for 5 days at 4 °C. Research showed that nicotinamide contributes to reducing oxidative stress level by reducing PARP-1 mRNA gene expression and the protein level resulting in higher NAD+ availability, as well as improving energy metabolism and NADPH levels in fruits, regardless of whether they are exposed to UV-C. The above effects cause fruits treated with nicotinamide to be characterised by higher anti-radical activity, and a lower level of reactive oxygen species in the tissue.

The Effects of Poly-γ-Glutamic Acid on the Postharvest Physiology and Quality of Strawberry cv. Hongyan during Cold Storage

This study investigated the effects of poly-γ-glutamic acid (γ-PGA) on the postharvest physiology and quality of the strawberry cv. Hongyan during cold storage. The results showed that all concentrations of γ-PGA improved decay control and strawberry preservation by enhancing antioxidant capacity, delaying the softening process, and maintaining fruit quality, especially for 100 mg·L-1 γ-PGA. After 14 days of treatment, compared with control, 100 mg·L-1 γ-PGA decreased weight loss, decay rate, and index by 21.9%, 75.0%, and 66.7% and increased the total antioxidant capacity by 43.5% through antioxidant enzymes. In addition, 100 mg·L-1 γ-PGA increased fruit firmness by 53.6% by decreasing the activities of polygalacturonase, pectin lyase, cellulase, and β-galactosidase. In terms of color quality, 100 mg·L-1 γ-PGA improved the values of lightness and yellowness by 30.9% and 52.8%. As regards nutritional quality, 100 mg·L-1 γ-PGA increased the contents of protein, soluble sugars, vitamin C, and total phenols by 106.6%, 80.6%, 51.2%, and 78.4%. In terms of sensory quality, 100 mg·L-1 γ-PGA increased the soluble solids' content by 19.0% and decreased the titrated acids' content by 21.1%, which increased the sugar-acid ratio by 50.9%. Our findings suggest that 100 mg·L-1 γ-PGA can be used to improve the decay control and preservation of strawberry cv. Hongyan under cold storage.

Edible coating enriched with cinnamon oil reduces the oxidative stress and improves the quality of strawberry fruit stored at room temperature

BACKGROUND

The present study aimed to assess the impact of a starch/gelatine coating containing cinnamon oil on selected quality attributes and redox status in strawberry fruit stored at room temperature (72 h).

RESULTS

Research showed that the application of cinnamon oil to an edible coating allows an improvement of the quality of strawberry fruit stored at room temperature. The cinnamon oil coating inhibits the development of yeast and mould, and reduces loss of soluble solids and ascorbic acid during 72 h storage at room temperature. Moreover, the coating with cinnamon oil clearly reduced the level of oxidative stress, which was manifested by a lower level of reactive oxygen species, as well as a lower activity of antioxidant enzymes. The elimination of oxidative stress in the cinnamon oil-coated fruit also contributed to lower PARP1 mRNA expression, inhibiting the metabolism of NAD⁺ and reducing ATP losses.

CONCLUSION

The coating of strawberry fruit with a starch/gelatine biofilm containing cinnamon oil is an effective method for delaying postharvest senescence of fruit and the storage degradation of tissue. © 2023 Society of Chemical Industry.

One-time ozone treatment improves the postharvest quality and antioxidant activity of Actinidia arguta fruit

The major aim of this study was to check the effect of one-time ozonation on selected quality parameters and antioxidant status of Actinidia arguta fruit. For this purpose, A. arguta fruit was ozonated with gas at a concentration of 10 and 100 ppm, which was carried out successively for 5, 15 and 30 min. Next, the selected quality attributes, antioxidants level as well as NADPH and mitochondrial energy metabolism in mini-kiwi fruit after ozonation were analysed. Our research has shown that ozonation reduced the level of yeast and mould without affecting the content of soluble solids or acidity. In turn, ozonation clearly influenced the antioxidant activity and the redox status of the fruit. The ozonated fruit was characterised by a lower level of ROS due to the higher level of low molecular weight antioxidants, as well as the higher activity of superoxide dismutase and catalase. In addition, improved quality and antioxidant activity of the fruit were indirectly due to improved energy metabolism and NADPH level. The ozonated fruit showed a higher level of ATP, due to both higher activity of succinate dehydrogenase and higher availability of NADH. Moreover, the increased level of NAD⁺ and the activity of NAD⁺ kinase and glucose-6-phosphate dehydrogenase contributed to higher levels of NADPH in the fruit.

Ozonation process causes changes in PARP-1 expression and the metabolism of NADPH in strawberry fruit during storage

In this study, the effect of ozonation process on the poly(ADP-ribose) polymerase 1 gene expression (PARP-1) and related the NADPH metabolism in strawberry fruit during storage was determined. Our results showed that ozonation with gas at both 10 and 100 ppm concentrations increased the expression of PARP-1 in the fruit during storage. Furthermore, the ozonation process initially increased the level of NAD⁺ and NADH in the fruit, which corresponds to a higher ATP level. The storage of the fruit in an ozone atmosphere also contributed to increased activity of the NAD⁺ kinase, leading to increased levels of NADP⁺ . In turn, the higher activity of glucose-6-phosphate dehydrogenase caused the ozonated fruit to show a higher level of NADPH. However, as the storage period extended and thus with increasing expression of PARP-1 in the ozonated fruit, the level of NAD⁺ decreased. In general, the ozonated fruit, which had a higher level of NADPH, showed a higher content of reduced glutathione, which in turn contributed to an increase in the antioxidant activity of the fruit and, ultimately, to a lower accumulation of reactive oxygen species.

Phytosulfokine α (PSKα) delays senescence and reinforces SUMO1/SUMO E3 ligase SIZ1 signaling pathway in cut rose flowers (Rosa hybrida cv. Angelina)

Roses are widely used as cut flowers worldwide. Petal senescence confines the decorative quality of cut rose flowers, an impressively considerable economic loss. Herein, we investigated the SUMO1/SUMO E3 ligase SIZ1 signaling pathway during bud opening, and petal senescence of cut rose flowers. Our results exhibited that the higher expression of SUMO1 and SUMO E3 ligase SIZ1 during bud opening was accompanied by lower endogenous H2O2 accumulation arising from higher expression and activities of SOD, CAT, APX, and GR, promoting proline accumulation by increasing P5CS expression and activity and enhancing GABA accumulation by increasing GAD expression and activity. In harvested flowers, lower expressions of SUMO1 and SUMO E3 ligase SIZ1 during petal senescence were associated with higher endogenous H2O2 accumulation due to lower expression and activities of SOD, CAT, APX, and GR. Therefore, promoting the activity of the GABA shunt pathway as realized by higher expression and activities of GABA-T and SSADH accompanied by increasing OAT expression and activity for sufficiently supply proline in rose flowers during petal senescence might serve as an endogenous antisenescence mechanism for slowing down petals senescence by avoiding endogenous H2O2 accumulation. Following phytosulfokine α (PSKα) application, postponing petal senescence in cut rose flowers could be ascribed to higher expression of SUMO1 and SUMO E3 ligase SIZ1 accompanied by higher expression and activities of SOD, CAT, APX, and GR, higher activity of GABA shunt pathway as realized by higher expression and activities of GAD, GABA-T, and SSADH, higher expression and activities of P5CS and OAT for supplying proline and higher expression of HSP70 and HSP90. Therefore, our results highlight the potential of the PSKα as a promising antisenescence signaling peptide in the floriculture industry for postponing senescence and extending the vase life of cut rose flowers.

Delaying Broccoli Floret Yellowing by Phytosulfokine α Application During Cold Storage

During postharvest life, broccoli suffers from floret yellowing confining its economic and nutritional value. The objective of the present study was to explore the mechanisms employed by phytosulfokine α (PSKα) at 150 nM for delaying floret yellowing in broccoli during storage at 4°C for 28 days. Our results showed that the higher endogenous accumulation of hydrogen sulfide (H₂S) resulting from the higher gene expression and activities of l-cysteine desulfhydrase (LCD) and d-cysteine desulfhydrase (DCD) in broccoli floret treated with 150 nM PSKα may serve as an endogenous signaling molecule for delaying senescence. Moreover, the suppressed ethylene biosynthesis in broccoli floret treated with 150 nM PSKα might be ascribed to lower gene expression and activities of ACC synthase (ACS) and ACC oxidase (ACO). Furthermore, lower gene expression and activities of Mg²⁺ dechelatase (MDC), pheophytinase (PPH), and pheophorbide a oxygenase (PaO) might be the reasons for the higher accumulation of chlorophyll in broccoli floret treated with 150 nM PSKα. Based on our findings, exogenous PSKα application could be employed as signaling bioactive hormone for retarding floret yellowing of broccoli during storage at 4°C for 28 days.

Employing phytosulfokine α (PSKα) for delaying broccoli florets yellowing during cold storage

The yellowing of florets limits the economic and nutritional value of broccoli during postharvest. We investigated mechanisms of action of 150 nM phytosulfokine α (PSKα) for delaying florets yellowing in broccoli during cold storage. Our results showed that SUMO E3 ligase (SIZ1) gene expression was higher in florets treated with PSKα, which may prevent endogenous H₂O₂ accumulation, resulting from the higher activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase. Besides, higher expression of methionine sulfoxide reductase and cysteine peroxiredoxin genes, concomitant with higher expression of heat shock proteins 70/90 genes, may arise from higherexpression of SIZ1 gene. Lower expression and activity of phospholipase D and lipoxygenase may be liable for membrane integrity protection featured by lower malondialdehyde accumulation in florets treated with PSKα. Additionally,florets treated with PSKα exhibited higher endogenous cytokinin accumulation which may arise from higher expression of isopentenyl transferase gene, concomitant with lower expression of cytokinin oxidase gene.

Controlling the Heterodimerisation of the Phytosulfokine Receptor 1 (PSKR1) via Island Loop Modulation

Phytosulfokine (PSK) is a phytohormone responsible for cell-to-cell communication in plants, playing a pivotal role in plant development and growth. The binding of PSK to its cognate receptor, PSKR1, is modulated by the formation of a binding site located between a leucine-rich repeat (LRR) domain of PSKR1 and the loop located in the receptor's island domain (ID). The atomic resolution structure of the extracellular PSKR1 bound to PSK has been reported, however, the intrinsic dynamics of PSK binding and the architecture of the PSKR1 binding site remain to be understood. In this work, we used atomistic molecular dynamics (MD) simulations and free energy calculations to elucidate how the PSKR1 island domain (ID) loop forms and binds PSK. Moreover, we report a novel "druggable" binding site which could be exploited for the targeted modulation of the PSKR1-PSK binding by small molecules. We expect that our results will open new ways to modulate the PSK signalling cascade via small molecules, which can result in new crop control and agricultural applications.