Proteomics analysis to understand the ABA stimulation of wound suberization in kiwifruit

Feruloyl Glyceride Mitigates Tomato Postharvest Rot by Inhibiting Penicillium expansum Spore Germination and Enhancing Suberin Accumulation

Postharvest rot, caused by Penicillium expansum, in tomatoes poses significant economic and health risks. Traditional control methods, such as the use of fungicides, raise concerns about pathogen resistance, food safety, and environmental impact. In search of sustainable alternatives, plant secondary metabolites, particularly phenolic compounds and their derivatives, have emerged as promising natural antimicrobials. Among these, feruloyl glyceride (FG), a water-soluble derivative of ferulic acid, stands out due to its antioxidant properties, antibacterial properties, and improved solubility. In this study, we provide evidence demonstrating FG is capable of inhibiting the spore germination of P. expansum and effectively reducing the incidence rate of Penicillium rot of tomatoes, without compromising quality. Electron microscopy observations combined with metabolite and transcriptomic analyses revealed that FG treatments resulted in enhanced suberin accumulation through promoting the expression of suberin synthesis related genes and, consequently, inhibited the growth and expansion of P. expansum on the fruits. This work sheds light on the mechanisms underlying FG's inhibitory effects, allowing its potential application as a natural and safe alternative to replace chemical fungicides for postharvest preservation.

Effects of AMF inoculation on the growth, photosynthesis and root physiological morphology of root-pruned Robinia pseudoacacia seedlings

Root pruning hinders the absorption and utilization of nutrients and water by seedlings in the short term. Arbuscular mycorrhizal fungi (AMF) are an important source of nutrient and water for seedlings except for the root system. However, the mechanism by which AMF affect the physiological growth of seedlings after root pruning has rarely been studied. In this study, a pot experiment was conducted through a three-compartment partition system to clarify the effects of Funneliformis mosseae (F. mosseae) strain BGC XJ07A on the physiological growth of root-pruned Robinia pseudoacacia seedlings. Five root pruning treatments (zero, one-fifth, one-fourth, one-third and one-half of the taproot length were removed) were applied to noninoculated seedlings and those inoculated with F. mosseae. The results showed that the presence of F. mosseae significantly increased the shoot and root biomasses, leaf photosynthetic rate, stomatal conductance and transpiration rate. The root projected area, root surface area, average root diameter, root density, root volume and number of root tips of the inoculated seedlings were higher than those without inoculation in all root pruning treatments. The root cytokinin, gibberellins and indole-3-acetic acid concentrations, but root abscisic acid concentration, were higher than those measured in the absence of inoculation in all root pruning treatments. Moreover, the changes in the root endogenous hormone concentrations of the seedlings were closely related to the root morphological development and seedling biomass. The AMF increased the soil available nitrogen, soil available phosphorus, soil available potassium and soil organic matter concentrations compared with the noninoculated treatment. These results indicate that AMF can alleviate the adverse effects of root pruning on the physiological growth of R. pseudoacacia and soil properties, and can provide a basis for AMF application to forest cultivation and the sustainable development of forest ecosystems.

Effect of Mowing on Wheat Growth at Seeding Stage

Winter wheat is used as forage at the tillering stage in many countries; however, the regrowth pattern of wheat after mowing remains unclear. In this study, the growth patterns of wheat were revealed through cytological and physiological assessments as well as transcriptome sequencing. The results of agronomic traits and paraffin sections showed that the shoot growth rate increased, but root growth was inhibited after mowing. The submicroscopic structure revealed a decrease in heterochromatin in the tillering node cell and a change in mitochondrial shape in the tillering node and secondary root. Analysis of the transcriptome showed the number of differentially expressed genes (DEGs) involved in biological processes, cellular components, and molecular functions; 2492 upregulated DEGs and 1534 downregulated DEGs were identified. The results of the experimental study showed that mowing induced expression of DEGs in the phenylpropanoid biosynthesis pathway and increased the activity of PAL and 4CL. The upregulated DEGs in the starch and sucrose metabolism pathways and related enzyme activity alterations indicated that the sugar degradation rate increased. The DEGs in the nitrogen metabolism pathway biosynthesis of the amino acids, phenylpropanoid biosynthesis metabolism, and in the TCA pathway also changed after mowing. Hormone content and related gene expression was also altered in the tillering and secondary roots after mowing. When jasmonic acid and ethylene were used to treat the wheat after mowing, the regeneration rate increased, whereas abscisic acid inhibited regrowth. This study revealed the wheat growth patterns after mowing, which could lead to a better understanding of the development of dual-purpose wheat.

Wounding induces suberin deposition, relevant gene expressions and changes of endogenous phytohormones in Chinese yam (Dioscorea opposita) tubers

Wounds on Chinese yam (Dioscorea opposita ) tubers can ocurr during harvest and handling, and rapid suberisation of the wound is required to prevent pathogenic infection and desiccation. However, little is known about the causal relationship among suberin deposition, relevant gene expressions and endogenous phytohormones levels in response to wounding. In this study, the effect of wounding on phytohormones levels and the expression profiles of specific genes involved in wound-induced suberisation were determined. Wounding rapidly increased the expression levels of genes, including PAL , C4H , 4CL , POD , KCSs , FARs , CYP86A1 , CYP86B1 , GPATs , ABCGs and GELPs , which likely involved in the biosynthesis, transport and polymerisation of suberin monomers, ultimately leading to suberin deposition. Wounding induced phenolics biosynthesis and being polymerised into suberin poly(phenolics) (SPP) in advance of suberin poly(aliphatics) (SPA) accumulation. Specifically, rapid expression of genes (e.g. PAL , C4H , 4CL , POD ) associated with the biosynthesis and polymerisation of phenolics, in consistent with SPP accumulation 3days after wounding, followed by the massive accumulation of SPA and relevant gene expressions (e.g. KCSs , FARs , CYP86A1 /B1 , GPATs , ABCGs , GELPs ). Additionally, wound-induced abscisic acid (ABA) and jasmonic acid (JA) consistently correlated with suberin deposition and relevant gene expressions indicating that they might play a central role in regulating wound suberisation in yam tubers.

The combination treatment of chlorogenic acid and sodium alginate coating could accelerate the wound healing of pear fruit by promoting the metabolic pathway of phenylpropane

Water loss and microbial infection induced by mechanical injury are the main sources of harvested loss of fruits and vegetables. Plenty studies have shown that regulating phenylpropane-related metabolic pathways can effectively accelerate wound healing. The combination treatment of chlorogenic acid and sodium alginate coating on postharvest wound healing of pear fruit were investigated in this work. The result shows combination treatment reduced weight loss and disease index of the pears, enhanced texture of healing tissues, maintained the integrity of cell membrane system. Moreover, chlorogenic acid increased the content of total phenols and flavonoids, and ultimately leads to the accumulation of suberin poly phenolic (SPP) and lignin around wound cell wall. Activities of phenylalanine metabolism-related enzymes (PAL, C4H, 4CL, CAD, POD and PPO) in wound-healing tissue were enhanced. The contents of major substrates such as trans-cinnamic, p-coumaric, caffeic, and ferulic acids also increased. The presented results suggested that the combination treatment of chlorogenic acid and sodium alginate coating stimulated wound healing in pears by elevating the phenylpropanoid metabolism pathway, so that maintain high postharvest fruit quality.

Disruption of the ABA1 encoding zeaxanthin epoxidase caused defective suberin layers in Arabidopsis seed coats

Suberin, a complex polyester deposited in the seed coat outer integument, acts as a hydrophobic barrier to control the movement of water, ions, and gas. However, relatively little is known about the signal transduction involved in suberin layer formation during seed coat development. In this study, the effect of the plant hormone abscisic acid (ABA) on suberin layer formation in seed coats was investigated by characterizing mutations in Arabidopsis related to ABA biosynthesis and signaling. Seed coat permeability to tetrazolium salt was noticeably elevated in aba1-1 and abi1-1 mutants, but not significantly altered in snrk2.2/3/6, abi3-8, abi5-7, and pyr1pyl1pyl2pyl4 quadruple mutants compared with that in the wild-type (WT). ABA1 encodes a zeaxanthin epoxidase that functions in the first step of ABA biosynthesis. aba1-1 and aba1-8 mutant seed coats showed reduced autofluorescence under UV light and increased tetrazolium salt permeability relative to WT levels. ABA1 disruption resulted in decreased total seed coat polyester levels by approximately 3%, with a remarkable reduction in levels of C24:0 ω-hydroxy fatty acids and C24:0 dicarboxylic acids, which are the most abundant aliphatic compounds in seed coat suberin. Consistent with suberin polyester chemical analysis, RT-qPCR analysis showed a significant reduction in transcript levels of KCS17, FAR1, FAR4, FAR5, CYP86A1, CYP86B1, ASFT, GPAT5, LTPG1, LTPG15, ABCG2, ABCG6, ABCG20, ABCG23, MYB9, and MYB107, which are involved in suberin accumulation and regulation in developing aba1-1 and aba1-8 siliques, as compared with WT levels. Together, seed coat suberization is mediated by ABA and partially processed through canonical ABA signaling.

The involvement of nitric oxide and ethylene on the formation of endodermal barriers in response to Cd in hyperaccumulator Sedum alfredii

Nitric oxide (NO) and ethylene are both important signaling molecules which participate in numerous plant development processes and environmental stress resistance. Here, we investigate whether and how NO interacts with ethylene during the development of endodermal barriers that have major consequences for the apoplastic uptake of cadmium (Cd) in the hyperaccumulator Sedum alfredii. In response to Cd, an increased NO accumulation, while a decrease in ethylene production was observed in the roots of S. alfredii. Exogenous supplementation of NO donor SNP (sodium nitroprusside) decreased the ethylene production in roots, while NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) had the opposite effect. The exogenous addition of NO affected the ethylene production through regulating the expression of genes related to ethylene synthesis. However, upon exogenous ethylene addition, roots retained their NO accumulation. The abovementioned results suggest that ethylene is downstream of the NO signaling pathway in S. alfredii. Regardless of Cd, addition of SNP promoted the deposition of endodermal barriers via regulating the genes related to Casparian strips deposition and suberization. Correlation analyses indicate that NO positively modifies the formation of endodermal barriers via the NO-ethylene signaling pathway, Cd-induced NO accumulation interferes with the synthesis of ethylene, leading to a deposition of endodermal barriers in S. alfredii.

Post-harvest chitosan treatment suppresses oxidative stress by regulating reactive oxygen species metabolism in wounded apples

Mechanical wound on fruit triggers the formation of reactive oxygen species (ROS) that weaken cell walls, resulting in post-harvest losses. This mechanism can be controlled by using fruit preservatives to stimulate fruit antioxidant enzyme activities for the detoxification of ROS. Chitosan is a safe and environmentally friendly preservative that modulates ROS in whole fruits and plant cells, but the effects of chitosan on the ROS metabolism of mechanically wounded apples during storage are unknown. Our study focused on exploring the effects of post-harvest chitosan treatment on ROS production, cell membrane integrity, and enzymatic and non-enzymatic antioxidant systems at fruit wounds during storage. Apple fruits (cv. Fuji) were artificially wounded, treated with 2.5% (w/v) chitosan, and stored at room temperature (21-25°C, RH = 81-85%) for 7 days. Non-wounded apples were used as healthy controls. The results showed that chitosan treatment stimulated the activities of NADPH oxidase and superoxide dismutase and increased the formation of superoxide anions and hydrogen peroxide in fruit wounds. However, malondialdehyde, lipoxygenase, and membrane permeability, which are direct biomarkers to evaluate lipid peroxidation and membrane integrity, were significantly decreased in the wounded fruits after chitosan treatment compared to the wounded control fruits. Antioxidant enzymes, such as peroxidase and catalase activities, were induced by chitosan at fruit wounds. In addition, ascorbate-glutathione cycle-related enzymes; ascorbate peroxide, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and the content of substrates, mainly ascorbic acid, dehydroascorbate, reduced glutathione, and glutathione, were increased at fruit wounds by chitosan compared to the wounded control fruits. Our results show that wounding stimulated the production of ROS or oxidative stress. However, treatment with chitosan triggered antioxidant systems to scavenge ROS and prevent loss of fruit membrane integrity. Therefore, chitosan promises to be a favorable preservative in inducing tolerance to stress and maintaining fruit quality.

MYB1R1 and MYC2 Regulate ω-3 Fatty Acid Desaturase Involved in ABA-Mediated Suberization in the Russet Skin of a Mutant of 'Dangshansuli' (Pyrus bretschneideri Rehd.)

Russeting, a disorder of pear fruit skin, is mainly caused by suberin accumulation on the inner part of the outer epidermal cell layers. ABA was identified as a crucial phytohormone in suberification. Here, we demonstrated that the ABA content in russet pear skin was higher than in green skin. Then, ABA was applied to explore the changes in phenotype and suberin composition coupled with RNA-Seq and metabolomics to investigate the probably regulatory pathway of ABA-mediated suberification. The results showed that ABA treatment increased the expression of ω-3 fatty acid desaturase (FAD) and the content of α-linolenic acid. We identified 17 PbFADs in white pear, and the expression of PbFAD3a was induced by ABA. In addition, the role of PbFAD3a in promoting suberification has been demonstrated by overexpression in Arabidopsis and VIGS assays in the fruitlets. GUS staining indicated that the promoter of PbFAD3a was activated by ABA. Furthermore, MYC2 and MYB1R1 have been shown to bind to the PbFAD3a promoter directly and this was induced by ABA via yeast one-hybrid (Y1H) screening and qRT-PCR. In summary, our study found that ABA induces the expression of MYC2 and MYB1R1 and activates the PbFAD3a promoter, contributing to the formation of russet pear skin. Functional identification of key transcription factors will be the goal of future research. These findings reveal the molecular mechanism of ABA-mediated suberization in the russet skin and provide a good foundation for future studies on the formation of russet skin.

Mechanical damages and packaging methods along the fresh fruit supply chain: A review

Mechanical damage of fresh fruit occurs throughout the postharvest supply chain leading to poor consumer acceptance and marketability. In this review, the mechanisms of damage development are discussed first. Mathematical modeling provides advanced ways to describe and predict the deformation of fruit with arbitrary geometry, which is important to understand their mechanical responses to external forces. Also, the effects of damage at the cellular and molecular levels are discussed as this provides insight into fruit physiological responses to damage. Next, direct measurement methods for damage including manual evaluation, optical detection, magnetic resonance imaging, and X-ray computed tomography are examined, as well as indirect methods based on physiochemical indexes. Also, methods to measure fruit susceptibility to mechanical damage based on the bruise threshold and the amount of damage per unit of impact energy are reviewed. Further, commonly used external and interior packaging and their applications in reducing damage are summarized, and a recent biomimetic approach for designing novel lightweight packaging inspired by the fruit pericarp. Finally, future research directions are provided.HIGHLIGHTSMathematical modeling has been increasingly used to calculate damage to fruit.Cell and molecular mechanisms response to fruit damage is an under-explored area.Susceptibility measurement of different mechanical forces has received attention.Customized design of reusable and biodegradable packaging is a hot topic of research.

Identification of genes and metabolic pathways involved in wounding-induced kiwifruit ripening

Fruit is constantly challenged by wounding events, inducing accelerated ripening and irreversible metabolic changes. However, cognate mechanisms that regulate this process are little known. To expand our knowledge of ripening metabolism induced by wounding, an artificial-wound global transcriptome investigation combined with metabolite profiling study was conducted in postharvest kiwifruit (Actinidia chinensis var. deliciosa (A. Chev.) A. Chev. 'Hayward'). Wounding treatment promoted fruit ripening, as demonstrated by changes in fruit firmness, ethylene production and respiration activity determined periodically during a ripening period of 8 d at room temperature. Calcium imaging using fluorescent probe Fluo-3 AM revealed spatial dynamics of Ca²⁺ signaling in the wounding area following 8d ripening. Several sugars including fructose, glucose, and sucrose as well as organic acids such as citric, succinic and galacturonic acid were increased by wounding. Changes of various amino acids in wounded-treated fruit, especially 5-oxoproline and valine along with alternations of soluble alcohols, like myo-inositol were detected. Gene expression analysis of the wounded fruit showed increased expression of genes that are mainly involved in defense response (e.g., AdTLP.1-3, AdPP2C.1-2, AdMALD1), calcium ion binding (e.g., AdCbEFh, AdCLR, AdANX), TCA cycle (e.g., AdMDH.1, AdMDH.2, AdCS), sugars (e.g., AdSUSA.1, AdSPS4, AdABFr), secondary metabolism (e.g., AdPAL.1-3, AdCCR, AdHCT.1-2), lipid processing (e.g., AdGELP.1-4, AdGELP) and pectin degradation (e.g., AdPE.1-2, AdPAE.1-2, AdPG.1-2) as well as in ethylene (AdERF7, AdERF1B, AdACO.1-4) and auxin (AdICE, AdAEFc, AdASII) synthesis and perception. Moreover, genes related to aquaporins, such as AdAQP2, AdAQP4 and AdAQP7 were down-regulated in fruit exposed to wounding. These results demonstrate multiple metabolic points of wounding regulatory control during kiwifruit ripening and provide insights into the molecular basis of wounding-mediated ripening.

Transcriptional regulation of KCS gene by bZIP29 and MYB70 transcription factors during ABA-stimulated wound suberization of kiwifruit (Actinidia deliciosa)

BACKGROUND

Our previous study has demonstrated that the transcription of AchnKCS involved in suberin biosynthesis was up-regulated by exogenous abscisic acid (ABA) during the wound suberization of kiwifruit, but the regulatory mechanism has not been fully elucidated.

RESULTS

Through subcellular localization analysis in this work, AchnbZIP29 and AchnMYB70 transcription factors were observed to be localized in the nucleus. Yeast one-hybrid and dual-luciferase assay proved the transcriptional activation of AchnMYB70 and transcriptional suppression of AchnbZIP29 on AchnKCS promoter. Furthermore, the transcription level of AchnMYB70 was enhanced by ABA during wound suberization of kiwifruit, but AchnbZIP29 transcription was reduced by ABA.

CONCLUSIONS

Therefore, it was believed that ABA enhanced the transcriptional activation of AchnMYB70 on AchnKCS by increasing AchnMYB70 expression. On the contrary, ABA relieved the inhibitory effect of AchnbZIP29 on transcription of AchnKCS by inhibiting AchnbZIP29 expression. These results gave further insight into the molecular regulatory network of ABA in wound suberization of kiwifruit.

Abscisic acid stimulates wound suberisation in kiwifruit (Actinidia chinensis) by regulating the production of jasmonic acid, cytokinin and auxin

Wounding induces a cascade of correlative physiological responses that lead to the repair of damaged tissue. In this study, the effect of wounding on suberin, endogenous hormones and their metabolic genes expression was observed during the wound healing of kiwifruit (Actinidia chinensis Planch.). In addition, the role of abscisic acid (ABA) in wound suberisation was investigated by analysing the coordinated regulation between ABA and other hormones. The wound healing process in kiwifruit could be divided into two stages including: (1) initial accumulation of suberin polyphenolic (SPP) and long carbon chain suberin polyaliphatic monomers (LSPA) before 24h; and (2) massive synthesis of SPP and very long carbon chain suberin polyaliphatic monomers (VLSPA) after 24h. ABA content rapidly increased and induced the jasmonic acid (JA) biosynthesis at the early stage of wound healing. ABA level gradually decreased with the expression of AchCYP707A genes, while the contents of trans-zeatin (t-ZT) and indole-3-acetic acid (IAA) steadily increased at the late stage of wound healing. Exogenous ABA stimulated JA and suberin monomers accumulation, but suppressed both t-ZT and IAA biosynthesis. The role of ABA in wound healing of kiwifruit might be involved in the coordination of both JA-mediated suberin monomers biosynthesis and t-ZT- and IAA-mediated formation of suberised cells via an interaction mechanism.

An integrated metabolic and transcriptomic analysis reveals the mechanism through which fruit bagging alleviates exocarp semi-russeting in pear fruit

Fruit semi-russeting is an undesirable quality trait that occurs in fruit production. It is reported that preharvest fruit bagging could effectively alleviate fruit exocarp semi-russeting, but the physiological and molecular mechanisms remain unclear. In the present study, we performed an in-depth investigation into pear fruit semi-russeting from morphologic, metabolic and transcriptomic perspectives by comparing control (semi-russeted) and bagged (non-russeted) 'Cuiguan' pear fruits. The results showed that significant changes in cutin and suberin resulted in pear fruit semi-russeting. Compared with the skin of bagged fruits, the skin of the control fruits presented reduced cutin contents accompanied by an accumulation of suberin, which resulted in fruit semi-russeting; α, ω-dicarboxylic acids accounted for the largest proportion of typical suberin monomers. Moreover, combined transcriptomic and metabolic analysis revealed a series of genes involved in cutin and suberin biosynthesis, transport and polymerization differentially expressed between the two groups. Furthermore, the expression levels of genes involved in the stress response and in hormone biosynthesis and signaling were significantly altered in fruits with contrasting phenotypes. Finally, a number of transcription factors, including those of the MYB, NAC, bHLH and bZIP families, were differentially expressed. Taken together, the results suggest that the multilayered mechanism through which bagging alleviates pear fruit semi-russeting is complex, and the large number of candidate genes identified provides a good foundation for future functional studies.

Combined transcriptomics and proteomics analysis provides insight into metabolisms of sugars, organic acids and phenols in UV-C treated peaches during storage

3Ultraviolet-C (UV-C) irradiation is known for prolonging the shelf life of many fruit by regulating different pathways. To better understand the roles of UV-C treatment in regulating the metabolic pathways in peach fruit during cold storage, transcriptomics and proteomics approaches were applied to investigate changes in peaches treated with UV-C (1.5 kJ m^-2). The results showed that most differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were largely matched to carbohydrates and secondary metabolites. Further analysis found that peaches treated with UV-C exhibited higher sucrose, citric acid, malic acid, phenols, flavonoids and anthocyanins compared with untreated peaches. Proteomics and transcriptomics together indicated that changes of sugars and acids were associated with the expressions of invertase, sucrose synthase, fructokinase, malate dehydrogenase and citrate synthase. UV-C irradiation promoted the synthesis of phenols, flavonoids and anthocyanins by up-regulating expressions of phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, chalcone synthase, dihydroflavonol 4-reductase and UDP-glucose:flavonoid glucosyltransferase. In summary, this research explained the general molecular mechanism of the changes of sugars, acids and phenols in peaches in response to UV-C.

Regrowth strategies of Leymus chinensis in response to different grazing intensities

In temperate grassland ecosystems, grazing can affect plant growth by foraging, trampling, and excretion. The ability of dominant plant species to regrow after grazing is critical, since it allows the regeneration of photosynthetic tissues to support growth. We conducted a field experiment to evaluate the effects of different grazing intensities (control, light, medium, and heavy) on the physiological and biochemical responses of Leymus chinensis and the carbon (C) sources utilized during regrowth. Light grazing promoted regrowth and photoassimilate storage of L. chinensis, by increasing the net photosynthetic rate (P_n ), photosynthetic quenching, light interception, sugar accumulation, sucrose synthase activities, and fructose supply from stems. At medium grazing intensity, L. chinensis had low P_n , light interception, and sugar accumulation, but higher expression of a sucrose transporter gene (LcSUT1) and water-use efficiency, which reflected a tendency to store C in belowground to promote survival. This strategy was associated with regulation by abscisic acid (ABA), jasmonate, and salicylic acid (SA) signaling. However, L. chinensis tolerated heavy grazing by increased ABA and jasmonate-induced promotion of C assimilation and osmotic adjustment, combined with photoprotection against photo-oxidation, suggesting a strategy based on regrowth. In addition, stems were the main C source organs and energy supply rather than roots. Simultaneously, SA represented a weaker defense than ABA and jasmonate. Therefore, L. chinensis adopted different strategies for regrowth under different grazing intensities, and light grazing promoted regrowth the most. Our results demonstrate the regulation of C reserves utilization by phytohormones, and this regulation provides an explanation for recent results about grazing responses.

Utilisation of Toluidine blue O pH 4.0 and histochemical inferences in plant sections obtained by free-hand

For the observation of plant material under a light microscope, free-hand sectioning is usually the fastest and most practical procedure. The staining of the obtained cuts is a crucial step and the action mechanism of the dye is variable. Toluidine blue O is a cationic dye whose metachromatic potential for free-hand sections has long been known. Thus, this work aimed at analysing the performance of Toluidine blue O for this type of sectioning with a systematic and comparative approach. The action of Toluidine blue O pH 4.0 was tested for both fresh and previously clarified free-hand sections from leaves of different species of plant. These sections were compared with sections embedded in glycol-methacrylate resin stained with the same dye or submitted to different histochemical tests. The fresh sections obtained by free-hand and stained with Toluidine blue O permitted the accomplishment of histochemical inferences, with the advantage of maintaining the natural colours from the tissues. The previously clarified sections presented the advantage of having a clearer image, allowing a better cellular delimitation. We concluded that Toluidine blue O is very informative for sections of plant material obtained by free-hand, being, therefore, a procedure that is fast, inexpensive and with excellent results.

The Jasmonic Acid Pathway Positively Regulates the Polyphenol Oxidase-Based Defense against Tea Geometrid Caterpillars in the Tea Plant (Camellia sinensis)

Polyphenol oxidases (PPOs) as inducible defense proteins, contribute to tea (Camellia sinensis) resistance against tea geometrid larvae (Ectropis grisescens), and this resistance has been associated with the jasmonic acid (JA) signaling by testing geometrid performance in our previous work. However, the regulation of PPO-based defense by JA and other hormone signaling underlying these defense responses is poorly understood. Here, we investigated the role of phytohormones in regulating the PPO response to tea geometrids. We profiled levels of defense hormones, PPO activity and CsPPO genes in leaves infested with tea geometrids. Then, hormone levels were manipulated by exogenous application of methyl jasmonate (MeJA), gibberellin acid (GA₃), abscisic acid (ABA), JA biosynthesis inhibitors (sodium diethyldithiocarbamate trihydrate, DIECA and salicylhydroxamic acid, SHAM) and GA inhibitor (uniconazole, UNI). Upon geometrid attack, JA levels significantly increased, whereas GA levels notably decreased and ABA level was slightly decreased. And the PPO activity significantly increased in line with the transcript levels of CsPPO2 and CsPPO4 but not CsPPO1. There were an obvious antagonistic cross-talk between JA and GA signals and an association among JA signals, PPO response and herbivore resistance in tea plants. Pretreatment with MeJA increased PPO activity by activating the transcripts of CsPPO2 and CsPPO4, whereas application of JA inhibitor DIECA suppressed PPO activity. GA₃ strongly enhanced PPO activity, but ABA did not alter PPO activity. These findings strongly suggest that JA is a central player in PPO-mediated tea resistance against tea geometrids in a manner that prioritizes defense over growth.

ABF2 and MYB transcription factors regulate feruloyl transferase FHT involved in ABA-mediated wound suberization of kiwifruit

Suberin is a cell-wall biopolymer with aliphatic and aromatic domains that is synthesized in the wound tissues of plants in order to restrict water loss and pathogen infection. ω-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (FHT) is required for cross-linking of the aliphatic and aromatic domains. ABA is known to play a positive role in suberin biosynthesis but it is not known how it interacts with FHT. In this study, the kiwifruit (Actinidia chinensis) AchnFHT gene was isolated and was found to be localized in the cytosol. Transient overexpression of AchnFHT in leaves of Nicotiana benthamiana induced massive production of ferulate, ω-hydroxyacids, and primary alcohols, consistent with the in vitro ability of AchnFHT to catalyse acyl-transfer from feruloyl-CoA to ω-hydroxypalmitic acid and 1-tetradecanol. A regulatory function of four TFs (AchnABF2, AchnMYB4, AchnMYB41, and AchnMYB107) on AchnFHT was identified. These TFs localized in the nucleus and directly interacted with the AchnFHT promoter in yeast one-hybrid assays. Dual-luciferase analysis indicated that AchnABF2, AchnMYB41, and AchnMYB107 activated the AchnFHT promoter while AchnMYB4 repressed it. These findings were supported by the results of transient overexpression in N. benthamiana, in which AchnABF2, AchnMYB41, and AchnMYB107 induced expression of suberin biosynthesis genes (including FHT) and accumulation of suberin monomers, whilst AchnMYB4 had the opposite effect. Exogenous ABA induced the expression of AchnABF2, AchnMYB41, AchnMYB107, and AchnFHT and induced suberin monomer formation, but it inhibited AchnMYB4 expression. In addition, fluridone (an inhibitor of ABA biosynthesis) was found to counter the inductive effects of ABA. Activation of suberin monomer biosynthesis by AchnFHT was therefore controlled in a coordinated way by both repression of AchnMYB4 and promotion of AchnABF2, AchnMYB41, and AchnMYB107.

MYB41, MYB107, and MYC2 promote ABA-mediated primary fatty alcohol accumulation via activation of AchnFAR in wound suberization in kiwifruit

Wound damage triggers the accumulation of abscisic acid (ABA), which induces the expression of a large number of genes involved in wound suberization in plants. Fatty acyl-CoA reductase (FAR) catalyzes the generation of primary fatty alcohols by the reduction of fatty acids in suberin biosynthesis. However, the regulatory effects of transcription factors (TFs) on AchnFAR in response to ABA are unexplored. In this study, kiwifruit AchnFAR displayed a biological function analogous to that of FAR in transiently overexpressed tobacco (Nicotiana benthamiana) leaves. The positive role of TFs, including AchnMYB41, AchnMYB107, and AchnMYC2, in the regulation of AchnFAR was identified. The three TFs could individually bind to the AchnFAR promoter to activate gene transcription in yeast one-hybrid and dual-luciferase assays. Transient overexpression of TFs in tobacco leaves resulted in the upregulation of aliphatic synthesis genes (including FAR) and the increase in aliphatics, including primary alcohols, α,ω-diacids, ω-hydroxyacids, and fatty acids. Moreover, exogenous ABA treatment elevated TF-mediated AchnFAR expression and the accumulation of primary alcohols. Conversely, fluridone, an inhibitor of ABA biosynthesis, suppressed the expression of AchnFAR and TF genes and reduced the formation of primary alcohols. The results indicate that AchnMYB41, AchnMYB107, and AchnMYC2 activate AchnFAR transcription to promote ABA-mediated primary alcohol formation in wound suberization in kiwifruit.

Role of Pea LTPs and Abscisic Acid in Salt-Stressed Roots

Lipid transfer proteins (LTPs) are a class of small, cationic proteins that bind and transfer lipids and play an important role in plant defense. However, their precise biological role in plants under adverse conditions including salinity and possible regulation by stress hormone abscisic acid (ABA) remains unknown. In this work, we studied the localization of LTPs and ABA in the roots of pea plants using specific antibodies. Presence of LTPs was detected on the periphery of the cells mainly located in the phloem. Mild salt stress (50 mM NaCI) led to slowing plant growth and higher immunostaining for LTPs in the phloem. The deposition of suberin in Casparian bands located in the endoderma revealed with Sudan III was shown to be more intensive under salt stress and coincided with the increased LTP staining. All obtained data suggest possible functions of LTPs in pea roots. We assume that these proteins can participate in stress-induced pea root suberization or in transport of phloem lipid molecules. Salt stress increased ABA immunostaining in pea root cells but its localization was different from that of the LTPs. Thus, we failed to confirm the hypothesis regarding the direct influence of ABA on the level of LTPs in the salt-stressed root cells.

Unveiling the Mechanisms for the Plant Volatile Organic Compound Linalool To Control Gray Mold on Strawberry Fruits

Fungal infections significantly alter the emissions of volatile organic compounds (VOCs) by plants, but the mechanisms for VOCs affecting fungal infections of plants remain largely unknown. Here, we found that infection by Botrytis cinerea upregulated linalool production by strawberries and fumigation with linalool was able to inhibit the infection of fruits by the fungus. Linalool treatment downregulated the expression of rate-limiting enzymes in the ergosterol biosynthesis pathway, and this reduced the ergosterol content in the fungi cell membrane and impaired membrane integrity. Linalool treatment also caused damage to mitochondrial membranes by collapsing mitochondrial membrane potential and also downregulated genes involved in adenosine triphosphate (ATP) production, resulting in a significant decrease in the ATP content. Linalool treatment increased the levels of reactive oxygen species (ROS), in response to which the treated fungal cells produced more of the ROS scavenger pyruvate. RNA-Seq and proteomic analysis data showed that linalool treatment slowed the rates of transcription and translation.

Positive Regulation of the Transcription of AchnKCS by a bZIP Transcription Factor in Response to ABA-Stimulated Suberization of Kiwifruit

Wound-induced suberization is an essentially protective healing process for wounded fruit to reduce water loss and microbial infection. It has been demonstrated that abscisic acid (ABA) could promote wound suberization, but the molecular mechanism of ABA regulation remains little known. In this study, the transcript level of Achn030011 (designated as AchnKCS), coding a β-ketoacyl-coenzyme A synthase (KCS) involved in suberin biosynthesis, was found to be significantly upregulated by ABA in wounded kiwifruit. A bZIP transcription factor (Achn270881), a possible downstream transcription factor in the ABA signaling pathway, was screened and designated as AchnbZIP12 according to its homology with related Arabidopsis transcription factors. A yeast one-hybrid assay demonstrated that AchnbZIP12 could interact with the AchnKCS promoter. Furthermore, significant trans-activation of AchnbZIP12 on AchnKCS was verified. The transcript level of AchnbZIP12 was also upregulated upon treatment with ABA. These results imply that AchnbZIP12 acts as a positive regulator in ABA-mediated AchnKCS transcription during wound suberization of kiwifruit.

Transcript analyses reveal a comprehensive role of abscisic acid in modulating fruit ripening in Chinese jujube

BACKGROUND

Chinese jujube (Ziziphus jujuba Mill.) is a non-climacteric fruit; however, the underlying mechanism of ripening and the role of abscisic acid involved in this process are not yet understood for this species.

RESULTS

In the present study, a positive correlation between dynamic changes in endogenous ABA and the onset of jujube ripening was determined. Transcript analyses suggested that the expression balance among genes encoding nine-cis-epoxycarotenoid dioxygenase (ZjNCED3), ABA-8'-hydroxylase (ZjCYP707A2), and beta-glucosidase (ZjBG4, ZjBG5, ZjBG8, and ZjBG9) has an important role in maintaining ABA accumulation, while the expression of a receptor (ZjPYL8), protein phosphatase 2C (ZjPP2C4-8), and sucrose nonfermenting 1-related protein kinase 2 (ZjSnRK2-2 and ZjSnRK2-5) is important in regulating fruit sensitivity to ABA applications. In addition, white mature 'Dongzao' fruit were harvested and treated with 50 mg L- 1 ABA or 50 mg L- 1 nordihydroguaiaretic acid (NDGA) to explore the role of ABA in jujube fruit ripening. By comparative transcriptome analyses, 1103 and 505 genes were differentially expressed in response to ABA and NDGA applications on the 1st day after treatment, respectively. These DEGs were associated with photosynthesis, secondary, lipid, cell wall, and starch and sugar metabolic processes, suggesting the involvement of ABA in modulating jujube fruit ripening. Moreover, ABA also exhibited crosstalk with other phytohormones and transcription factors, indicating a regulatory network for jujube fruit ripening.

CONCLUSIONS

Our study further elucidated ABA-associated metabolic and regulatory processes. These findings are helpful for improving strategies for jujube fruit storage and for gaining insights into understand complex non-climacteric fruit ripening processes.

Toluidine blue staining for cell and tissue biology applications

Toluidine blue (TB) staining either alone or in association with other methodologies has the potential to answer a variety of biological questions regarding the human, animal and plant tissues or cells. In this brief review, we not only report the primary use of TB to detect the anionic substrates and availability of their binding sites, but also unveil the resulting applications of TB staining in biological research. Among these applications, the uses of TB staining to identify the changes in chromatin DNA-protein complexes, nucleolus location, and extracellular matrix proteoglycan complexes associated with different physiological and pathological events are described. The usefulness of TB staining to monitor the effects elicited by environmental insults on chromatin and intercalation of drugs into the DNA is also included.

Three Transcription Activators of ABA Signaling Positively Regulate Suberin Monomer Synthesis by Activating Cytochrome P450 CYP86A1 in Kiwifruit

Wound attack stimulates accumulation of abscisic acid (ABA) that activates a number of genes associated with wound suberization of plants. Cytochrome P450 fatty acid ω-hydroxylase CYP86A1 catalyzes ω-hydroxylation of fatty acids to form the ω-functionalized monomers that play a pivotal role in suberin synthesis. However, the transcriptional regulation of ABA signaling on AchnCYP86A1 has not been characterized in kiwifruit. In this study, AchnCYP86A1, a kiwifruit homolog of Arabidopsis AtCYP86A1, was isolated. AchnCYP86A1-overexpressed N. benthamiana leaves displayed that the AchnCYP86A1 functioned as a fatty acid ω-hydroxylase associated with synthesis of suberin monomer. The regulatory function of three transcription factors (TFs, including AchnMYC2, AchnMYB41 and AchnMYB107) on AchnCYP86A1 was identified. All the three TFs were localized in nucleus and could individually interact with AchnCYP86A1 promoter to activate gene expression in yeast one-hybrid and dual-luciferase assays. The findings were further demonstrated in transient overexpressed N. benthamiana, in which all TFs notably elevated the expression of aliphatic synthesis genes including CYP86A1 and the accumulation of ω-hydroxyacids, α, ω-diacids, fatty acids and primary alcohols. Moreover, exogenous ABA induced the expression of AchnMYC2, AchnMYB41 and AchnMYB107 that promoted AchnCYP86A1 involving in suberin monomer formation. Contrary to the inductive effects of ABA, however, fluridone (an inhibitor of ABA biosynthesis) inhibited the three TFs expression and suberin monomer formation. These results indicate that AchnMYC2, AchnMYB41 and AchnMYB107 positively regulate suberin monomer synthesis by activating AchnCYP86A1 promoter in response to ABA.

Integrating proteomic and transcriptomic analyses of loquat (Eriobotrya japonica Lindl.) in response to cold stress

The expression levels of many genes and the related proteins change and regulate physiological and metabolic processes that help the plant survive harsh environmental conditions under cold stress. Damage due to cold and freezing conditions often causes dynamic loss of loquat fruits in cultivated parts of northern China. To illustrate the mechanism of cold tolerance in the loquat, we combined the transcriptomic analysis with isobaric tags for relative and absolute quantification (iTRAQ) and RNA sequencing (RNA-Seq) data from loquat leaves under 4 °C treatment. The results showed 122,081 genes and 1210 differentially expressed genes (DEGs), while only 4582 proteins and 300 differential proteins (DEPs) were identified. Functional annotation and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis indicated that metabolic pathways and biosynthesis of secondary metabolites were the two most common pathways in transcriptional and translational processes in this study. Comparison analysis of the transcriptomic and proteomic profiles, only 27 of 3620 genes were found to be shared both in DEGs and DEPs. Further validation with Real-Time Quantitative RT-PCR analysis showed that the genes expression of NADP-dependent D-sorbitol-6-phosphate dehydrogenase, anthocyanin synthase and phenylalanine ammonia-lyase were consistent with the pattern of transcriptome profile, which suggested that these three genes might play vital roles in cold tolerance in loquat.