This study examined the role of brassinosteroid (BR) application in mitigating chilling injury (CI) in 'Donghong' kiwifruit during cold storage. BR markedly alleviated CI symptoms, reduced lignification, electrolyte leakage, and malondialdehyde accumulation. It suppressed ROS buildup (O₂·- and H₂O₂) and enhanced antioxidant capacity through elevated activities and gene expression of SOD, CAT, and enzymes in the AsA-GSH cycle. BR also increased unsaturated fatty acid content, inhibited phospholipid degradation, and improved membrane integrity by modulating related enzyme activities and gene expression. Furthermore, BR maintained higher energy status, as indicated by increased ATP and ADP levels, energy charge, and enhanced activities of H+-ATPase, Ca2+-ATPase, CCO, and SDH, along with their up-regulated gene expression. These results demonstrate that BR enhances chilling tolerance by regulating ROS metabolism, membrane lipid stability, and energy metabolism.

Aroma biosynthesis in postharvest kiwifruit is of great significance for fruit quality; yet, the underlying regulatory mechanisms remain unclear. This study investigated the dynamic changes and regulatory mechanisms governing ester aroma biosynthesis in postharvest kiwifruit. Ethylene accelerated fruit softening, sugar core formation, soluble solid accumulation, ethylene production, and ester biosynthesis, whereas 1-methylcyclopropene exerted the opposite effects. AcAAT1 was identified as a key acyltransferase gene responsible for ester biosynthesis. Functional analyses demonstrated that overexpression of AcAAT1 increased ester content, while its silencing reduced the ester compounds. Furthermore, transcription factor AcBBX19 was identified as a direct transcriptional repressor of AcAAT1. Ethylene signaling directly suppressed AcBBX19 expression. Protein interaction assays demonstrated that AcBBX19 physically interacts with AcbHLH153. Although AcbHLH153 cannot directly bind to the AcAAT1 promoter, it enhances the repressive activity of AcBBX19. Transient overexpression and silencing experiments confirmed that both proteins collaboratively inhibit AcAAT1 expression and ester biosynthesis. Collectively, our findings establish that ethylene promotes kiwifruit ester biosynthesis by suppressing the AcbHLH153-AcBBX19 transcriptional module, thereby alleviating the repression of the key gene AcAAT1. This study provides novel insights into the transcriptional regulatory network governing aroma formation in postharvest fruit.

Citrus green mold (CGM), caused by Penicillium digitatum, is a highly destructive fungal disease that impacts the citrus fruit industry on a global scale, leading to substantial economic losses. As a cinnamaldehyde derivative, trans-4-methoxycinnamaldehyde (MCA) is the preferred alternative for controlling CGM over chemical fungicides because it is less harmful to the environment. In this study, the efficacy of MCA in inhibiting both the mycelial growth and spore germination of P. digitatum was demonstrated. In addition, MCA alleviated CGM in postharvest navel orange fruit. A transcriptomic analysis was conducted to explore the underlying molecular antifungal mechanisms of MCA, revealing 2877 and 3315 differentially expressed genes (DEGs) influenced by MCA treatment at the MIC and minimum fungicidal concentration, respectively. Further Kyoto Encyclopedia of Genes and Genomes pathway analysis of these DEGs indicated that MCA significantly impacted pathways associated with energy metabolism, oxidative stress response, lipid metabolism, and amino acid metabolism-critical elements for sustaining the integrity and normal functioning of the plasma membranes and mitochondria in P. digitatum cells. Our biochemical assays, as well as observations via electron microscopy and propidium iodide staining, demonstrated that the MCA treatment modified mycelial morphology, altered conidial ultra-structure, compromised plasma membrane integrity, and hindered mitochondrial function and ergosterol biosynthesis. Collectively, these findings enhance the understanding of MCA's antifungal activity through its molecular mechanisms, positioning it as a promising agent for controlling postharvest CGM in citrus fruits.

This study aimed to clarify the regulatory effect of methyl jasmonate (MeJA) on the postharvest quality of cold-stored kiwifruit during shelf life. Physiological analyses showed that MeJA treatment significantly delayed fruit softening, suppressed ethylene production and respiratory intensity without significantly affecting total soluble solids content. Regarding aroma components, MeJA notably increased the accumulation of total volatile compounds, especially esters and ketones, thereby reshaping the fruit aroma profile. RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA) identified the MEblack module, which was enriched in fatty acid metabolism and closely associated with ester accumulation. MeJA upregulated key genes involved in aroma synthesis, including FAD, LOX, ADH, and AAT. Transient overexpression assays confirmed that AcAAT17, a key AAT gene, significantly enhanced AAT enzyme activity and ester accumulation. Collectively, MeJA improves the flavor quality of cold-stored kiwifruit by mediating transcriptional reprogramming of aroma biosynthesis pathways.

Juice sac granulation is a complex physiological disorder that significantly compromises the eating quality and postharvest longevity of ‘Majiayou’ pummelo (Citrus grandis L.). The exact mechanisms by which juice sac granulation in citrus fruit remain elusive, particularly at the genetic regulatory level. In this study, we conducted a comprehensive transcriptomic analysis using RNA-seq data from juice sac samples collected at three granulation stages (G0, G1, and G2) of ‘Majiayou’ pummelo fruit, and characterized a nuclear-localizated C2H2 zinc finger protein, CgZAT11, whose expression progressively increased during juice sac granulation. Online prediction of CgZAT11 binding elements was used to scan the Citrus grandis genome, combining transcriptomic data to screen for eight potentially differentially expressed target genes involved in lignin biosynthesis. Functional validation revealed that CgZAT11 induced pronounced lignin accumulation and secondary cell wall thickening in pummelo juice sacs by enhancing the transcriptional levels of the CgCAD8 and CgPOD16 genes. Through integrated molecular assays—including yeast one-hybrid, dual-luciferase reporter, and electromobility shift assay—we demonstrated that CgZAT11 directly activates CgCAD8 and CgPOD16 by specifically binding to their promoters, thereby enhancing our understanding of the regulatory network governing juice sac granulation. These findings establish CgZAT11 as a transcriptional activator coordinating lignin biosynthesis pathways during juice sac granulation, providing novel mechanistic insights into the transcriptional regulation of juice sac granulation in ‘Majiayou’ pummelo fruit.

Citrus sour rot (CSR), caused by a wound-invading fungus Geotrichum citri-aurantii, leads to significant deterioration in fruit quality and has garnered substantial economic losses in citrus production. Green-type antifungal products (GAPs) are promising eco-friendly alternatives for fungal disease management. However, the inhibition and disease resistance mechanism of the natural tropolone monoterpene hinokitiol (HIN) on CSR remain insufficient. This study investigated the efficacy and underlying mechanisms of HIN in conferring resistance against G. citri-aurantii in harvested 'Lane Late' navel oranges. In vivo assays showed that HIN substantially delayed CSR progression, reducing disease severity by 47.0 % at 6 d of G. citri-aurantii inoculation. Furthermore, HIN treatment markedly inhibited the decline in pericarp firmness and suppressed the increases in relative conductivity, hydrogen peroxide level, and malondialdehyde content. By lowering the activities of cell wall-degrading enzymes and the expression of their encoding genes, HIN helped maintain cell wall integrity (CWI), thereby delaying fruit softening induced by fungal infection. Navel oranges treated with HIN also maintained higher antioxidant capacity, with increased levels of non-enzymatic antioxidants. Additionally, there were enhancements in ROS-scavenging enzyme activities along with the upregulation of their encoding gene expressions. In the correlation analysis, we identified six CSR severity-related transcription factors (ERF014/098, bHLH035, WRKY40, ZAT11, and PAT1). Collectively, these results demonstrate that HIN treatment effectively confers resistance against G. citri-aurantii inoculation by maintaining CWI and establishing ROS homeostasis, making it a GAP for large-scale commercial application in citrus fruit storage.

The regulatory mechanisms through which trans-4-methoxycinnamaldehyde (MCA) treatment inhibited the development of fungal diseases in postharvest citrus fruits, particularly the widespread occurrence of citrus green mold (CGM) caused by Penicillium digitatum, remained inadequately understood. Herein, 0.4 g/L MCA treatment was found to effectively slow the progression of P. digitatum infection and reduce the severity of CGM in harvested navel orange, and many physiological traits were measured, including fruit firmness, electrolyte leakage, malondialdehyde level, and cell wall polysaccharides (pectin, water-soluble pectin, cellulose, and hemicellulose) contents, as well as cell wall-degrading enzymes activities and their encoding genes expression. The transcriptomic sequencing data revealed that MCA treatment significantly diminished the number of DEGs in fruits infected with P. digitatum when compared to healthy fruits. A total of 432 DEGs were identified among the three groups, including 42 DEGs associated with cell wall degradation and 29 TFs related to CGM resistance. Real-time PCR investigations verified that the expression levels of CsPME3, CsPG2, CsCLE1, CsXTH9, and most of the 10 TFs were up-regulated by MCA treatment, whereas the expression levels of CsGal6, CsMYB51, and CsWRKY7 were suppressed during the later stages of P. digitatum infection. Thus, our results collectively proved that these genes responsive to MCA may play crucial roles in maintaining cell wall integrity to enhance fruit resistance to CGM, suggesting that MCA treatment could represent a promising strategy for preventing postharvest fungal diseases in citrus fruits.

The content of reactive oxygen species (ROS) was closely associated with the postharvest quality and softening speed in kiwifruit. Here, the effects of blue light on postharvest softening and ROS metabolism of kiwifruit were studied. The results demonstrated that blue light with a wavelength of 420 nm resulted in a delay in the reduction of fruit firmness and accumulation of total soluble solids by augmenting 1,1- diphenyl-2-picrylhydrazyl scavenging rate and reducing the levels of malondialdehyde, hydrogen peroxide, and superoxide anion. Blue light concurrently enhanced the activity of superoxide dismutase (SOD) and catalase (CAT), as well as upregulated the expression levels of associated genes. Additionally, kiwifruit treated with blue light exhibited significantly elevated levels of ascorbic acid (AsA) and glutathione (GSH), along with reduced levels of oxidized AsA (DHA) and oxidized GSH (GSSG), in comparison to the control group. Also, blue light enhanced the activity of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), mono-DHAR (MDHAR), and GSH reductase (GR) enzymes in the AsA-GSH cycle, while it decreased the activity of AsA oxidase (AO) enzymes. Correspondingly, blue light induced the expression of genes related to AsA biosynthesis and the AsA-GSH cycle, while inhibiting the expression of the AcAO genes. Altogether, the findings of our study indicate that blue light effectively enhanced the ROS scavenging capacity of kiwifruit and preserved a high level of AsA content, then retarded its postharvest ripening and softening.

Kiwifruit postharvest softening properties were evaluated upon treatment with 10 mM D(+)-glucosamine hydrochloride (GAH, a hexokinase inhibitor). GAH effectively attenuated the loss of firmness, decreases of starch and protopectin contents, increase in soluble pectin, and reduction in sugar content, thereby promoting fruit quality. Transcriptome sequencing indicated significant enrichment of differentially expressed genes (DEGs) in those related to cell wall organization, carbohydrate metabolic processes, and protein phosphorylation. Weighted gene co-expression correlation network analysis revealed that genes encoding beta-amylase (BAM1-3/ 7-8), hexokinase (HXK4), fructokinase (FRK3/4), polygalacturonase (PG1), and pectate lyase (PEL) were considered key structural genes highly correlated with firmness. Furthermore, real-time quantitative PCR and correlation network analysis revealed that HXK4 expression significantly negatively correlated with that of calmodulin-binding transcription activator (CMTA5) and transcription factor (WRKY1b), whereas the two transcription factors and nine key structural genes were significantly positively correlated. Transient overexpression analysis suggested that AcHXK4 may perform dual roles, depending on either the catalytic activity or signaling function, and inhibit expression levels of WRKY1b, CMTA5, and their downstream genes related to starch and pectin degradation, subsequently delaying kiwifruit postharvest softening. These results offer novel perspectives on the regulatory mechanisms implicated in kiwifruit postharvest softening.

In plants, ABF (ABA-responsive element binding factor)/AREB (ABA-responsive element binding) proteins regulate processes such as abiotic stress response, pathogen defense, and seed germination. However, the specific function and regulatory networks of ABF/AREB transcription factors during fruit ripening remain largely unknown. In this study, we found that the expression level of SlABF4 is abundant in tomato fruits and gradually decreases during the ripening process. Functional analysis confirmed that SlABF4 was localized in the cell nucleus and responded to ABA treatment. To further investigate the function of SlABF4 in fruit ripening, we generated overexpressing SlABF4 lines and CRISPR/Cas9-slabf4 knockout mutants. Compared with wild type (WT), the onset of fruit ripening in OE-SlABF4 lines was delayed and ethylene production reduced, while the slabf4-deficient mutants showed accelerated fruit ripening and increased ethylene release. Meanwhile, transcriptomic and qRT-PCR analyses indicated that the expression levels of several fruit ripening-related transcriptional factors and ethylene-associated genes were downregulated in OE-SlABF4 lines and upregulated in CR-slabf4 mutants. Importantly, yeast one-hybrid (Y1H), dual-luciferase reporter assays and electrophoretic mobility shift assays (EMSA) demonstrated that SlABF4 directly binds to the promoters of ethylene biosynthesis genes (SlACS2 and SlACS12) and represses their expression. Moreover, we found that SlABF4 can physically interact with two key ripening-related transcription factors (SlFUL1 and SlMADS1) to regulate tomato fruit ripening in vivo and in vitro, while SlABF4 inhibited the expression of SlACS2 to modulate ethylene biosynthesis. Together, these findings expand our insights into the negative regulatory role and molecular mechanism of SlABF4 in the fruit ripening process, which will provide support for precise breeding designed to mediate fruit ripening in tomato.

Citrus sour rot is normally caused by Geotrichum citri-aurantii, which not only deteriorates fruit quality but also causes huge economic losses annually. The current study delves into the underlying in vitro antifungal mechanisms of hinokitiol and assesses its efficacy in controlling sour rot development on navel oranges infected by G. citri-aurantii. Both in vitro and in vivo examinations demonstrate that hinokitiol exhibits strong antifungal activity against G. citri-aurantii, with a minimum inhibitory concentration and minimum fungicidal concentration of 25.0 mg/liter, resulting in a significant reduction in citrus sour rot disease. Decreased blue fluorescence in calcofluor white staining and cell wall components have confirmed that hinokitiol disrupts the structural organization of the G. citri-aurantii cell wall. Additionally, hinokitiol induces abnormal mycelial growth, causing more severe deformities, dried blights, plasmalemma wall separation, mitochondrial decomposition, and cell permeabilization. Furthermore, hinokitiol increases the production of H2O2, O2•-, and MDA levels in G. citri-aurantii, resulting in permanent damage to cell membrane integrity, mitochondrial oxidative phosphorylation, and DNA function, ultimately triggering cell apoptosis. These results indicate that hinokitiol is a novel antifungal agent for controlling postharvest sour rot in citrus fruits. This study contributes new insights into the control of postharvest fungal decay and elucidates hinokitiol's antifungal mechanism against G. citri-aurantii.

The carotenoid content in kiwifruit undergoes dynamic changes during the ripening process, yet the underlying mechanism remains unclear. Herein, the variation in carotenoid content was investigated during the postharvest ripening process of kiwifruit (Actinidia valvata). The results demonstrated a gradual increase in total carotenoid content during postharvest ripening and softening, accompanied by a deepening of the yellow flesh. The levels of all five carotenoid components also exhibited an upward trend with fruit ripening, with lutein content being the highest among them, thus indicating its pivotal role as the most significant carotenoid component in kiwifruit. The expression analysis of genes associated with carotenoid metabolism during postharvest storage revealed an upward trend in the expression levels of biosynthesis-related genes, while a downward trend was observed for degradation-related genes. Notably, the lycopene beta-cyclase (LCYB) gene exhibited the highest expression levels, which were significantly and positively correlated with carotenoid content. A basic helix-loop-helix transcription factor protein, bHLH149, capable of binding to the LCYB promoter was identified through yeast one-hybrid library screening. The expression of bHLH149 increased during fruit ripening and showed a positive correlation with carotenoid content. As a nuclear localization protein, bHLH149 acts as a transcriptional activator and significantly enhances LCYB promoter activity, thereby promoting carotenoid biosynthesis. The collective findings suggest that bHLH149 may play a role in the carotenoid biosynthesis pathway during kiwifruit ripening by positively regulating the transcription of LCYB, thereby enhancing our comprehension of the regulatory network governing carotenoid biosynthesis in kiwifruit.

Ascorbic acid (AsA) degradation during postharvest storage significantly reduces the nutritional quality of kiwifruit. This study revealed that 1-methylcyclopropene (1-MCP) delayed postharvest softening and ethylene production, and it delayed AsA loss by suppressing ascorbate oxidase (AO) activity. Transcriptomic analysis identified 13 AcAO genes, with AcAO9 expression strongly induced during ripening and inhibited by 1-MCP. Transient overexpression and silencing of AcAO9 confirmed its role in regulating AO activity and AsA content. Furthermore, the zinc finger transcription factor AcZFP3 was shown to directly bind to the AcAO9 promoter and activate its expression. AcZFP3 itself was transcriptionally regulated by AcERF61, which bound to the AcZFP3 promoter. Functional assays demonstrated that both AcZFP3 and AcERF61 positively regulate AO activity and promote AsA degradation. Collectively, our results demonstrate that 1-MCP maintains postharvest AsA levels in kiwifruit via the AcERF61-AcZFP3-AcAO9 module to attenuate AO activity. These findings provide novel insights into the regulation of postharvest AsA metabolism in kiwifruit.

Evaluation of kiwifruit postharvest ripening properties was conducted following 2-O-α-D-Glucopyranosyl-L-ascorbic acid (AA-2αG) treatment. AA-2αG effectively reduced firmness loss and titratable acid (TA), delayed the rise in total soluble solid (TSS) and TSS/TA, suppressed the production of ethylene and the respiration rate, thereby retarding kiwifruit ripening. To evaluate the impact of AA-2αG on the antioxidant system and oxidative damage during kiwifruit ripening, the primary oxidant and antioxidant characteristics were measured subsequently. The AA-2αG-treated fruit showed elevated levels of antioxidant enzymes and gene expression (AcSOD, AcCAT, and AcAPX), ascorbic acid, total phenols, flavonoids, and antioxidant capacity, along with decreased levels of O2•- production rate, H2O2, malondialdehyde (MDA), polyphenol oxidase (PPO), lipoxygenase (LOX) activities, and decreased expression of their encoding genes in comparison to the control. These findings imply that AA-2αG could be a potential preservative to enhance antioxidant system, prevent oxidative injury, and delay the ripening processes in kiwifruit.

The study aimed to investigate the effects of blue light (BL) on the postharvest ripening and softening of kiwifruit. The postharvest ripening of kiwifruit were significantly inhibited by BL; 100 μmol m-2 s-1 light intensity exhibited the best effect. The delay of postharvest ripening of kiwifruit by BL was associated with the inhibition of total soluble solids accumulation, reduction in respiratory rate and ethylene production as well as 1-aminocyclopropane-1-carboxylate synthase and 1-aminocyclopropane-1-carboxylic acid oxidase activities. Moreover, it also inhibited starch degradation and related enzyme activities (α-amylase and β-amylase), prevented the degradation of protopectin, cellulose and hemicellulose while promoting the accumulation of water soluble pectin. Additionally, it suppressed the activities of polygalacturonase, pectinlyase, pectin methylesterase, and cellulase. Transcriptome and gene expression analyses showed that BL-treated kiwifruit had lower expression levels of genes involved in ethylene biosynthesis, starch degradation, and cell wall metabolism, compared with the dark controls. BL also altered transcription factor responses to light, such as v-myb avian myeloblastosis viral oncogene homolog (MYB) and basic helix-loop-helix (bHLH) families. In summary, this study analyzed the physiological and molecular mechanisms by which BL delays the postharvest ripening of kiwifruit and provides a new preservation method for the postharvest quality maintenance of kiwifruit.

The regulatory mechanisms underlying the salicylic acid (SA)-mediated inhibition of senescence in pummelo fruit, the largest known citrus variety, remain unclear. Herein, postharvest 0.3% SA treatment was demonstrated to delay postharvest 'Jinshayou' pummelo senescence, as evidenced by the inhibitions in firmness loss, electrolyte leakage increase, and color change. Using comparative transcriptomic data, a total of 4367, 3769, and 1659 DEGs were identified between CK0 and CK60, CK0 and SA60, and CK60 and SA60, respectively. Further GO analysis revealed that DEGs were mainly implicated in the processes of cell wall modification and phenylpropanoid pathway during fruit senescence. More importantly, postharvest exogenous 0.3% SA treatment was observed to inhibit CWDEs activities and their encoding gene expression, retain higher protopectin, cellulose, and hemicelluloses contents, as well as reduce WSP content, thus maintaining cell wall structure. These findings collectively indicated that postharvest SA treatment was a green and useful preservative for alleviating fruit senescence and prolonging the storage life of harvested 'Jiashayou' pummelo fruit.

Once fruit were commercially harvested from vines, starch is degraded into soluble sugars such as sucrose, glucose, and fructose, which determine kiwifruit's nutritional and commercial quality. Glucose and fructose are the main sugars in mature kiwifruit, followed by sucrose. The expression of genes related to sugar metabolism during kiwifruit postharvest ripening is little-studied, so we identified a set of putative kiwifruit sugar metabolism genes containing three cell wall inverters (CWINVs), five fructokinases (FKs), five hexokinases (HXKs), five sucrose phosphate synthases (SPSs), six sucrose synthases (SUSs), and fourteen neutral invertases (NINVs). Phylogenetic analyses of Arabidopsis thaliana, kiwifruit, and tomato identified orthologous groups among them. AcCWINV1 and AcNINV3 transcription decreased as fruit sugar levels increased, but increased after 1-methylcyclopropene (1-MCP) application. AcFK1, AcFK2, AcHXK1, AcHXK2, AcSPS1, AcSPS5, AcSUS2, and AcNINV10 exhibited fruit-expressed, up-regulated profiles during postharvest ripening and were inhibited by 1-MCP, suggesting that they are involved in fruit sugar accumulation. Our results elucidate the genomic organizations, evolutionary characteristics, and expression profiling of sugar metabolism genes during kiwifruit postharvest stages, paving the way for further functional verification of sugar metabolism genes.

Cucumber fruit is very sensitive to chilling injury, which rapidly depreciates their commodity value. Herein, the effect of fucoidan treatment on cucumber under cold stress were investigated. Fucoidan treatment of cold-stored cucumber alleviated the occurrence of chilling injury, delayed weight loss, lowered electrolyte leakage and respiration rate, and retarded malondialdehyde accumulation. Different from the control fruit, fucoidan treated fruit showed a high level of fatty acid unsaturated content, fatty acid unsaturation, and unsaturation index and increased ω-FDAS activity, along with upregulated expression levels of CsSAD and CsFAD genes. Fucoidan reduced the phosphatidic acid content and membrane lipid peroxidation, lowered the phospholipase D (PLD) and lipoxygenase (LOX) activity, and downregulated the expression levels of CsPLD and CsLOX genes. Collectively, fucoidan treatment maintained the integrity of cell membrane in cold-stress cucumbers. The results provide a new prospect for the development of fucoidan as a preservative agent in the low-temperature postharvest storage of cucumbers.

Penicillium italicum is the causal agent of citrus blue mold, which is a major threat to the global citrus fruit industry. Antofine, a natural phenanthroindolizidine alkaloid, is water-soluble and exhibits a broad range of biological activities. However, whether it can inhibit P. italicum growth and the potential inhibitory mechanism remains to be elucidated. This study aimed to investigate the antifungal mechanism of antofine against P. italicum using scanning electron microscopy, transmission electron microscopy (TEM), propidium iodide staining, and tandem mass tag-labeled quantitative proteomic analysis. Antofine was found to exhibit its preeminent antifungal activity against P. italicum with a minimum inhibitory concentration of 1.56 mg/L and a minimum fungicidal concentration of 6.25 mg/L. The challenge test revealed that antofine inhibited the development of citrus blue mold during a 6-d P. italicum-infected period. Antofine acted on its potential multitargets to inhibit P. italicum growth by synergistically activating oxidative stress through accumulating excess reactive oxygen species, impairing membrane integrity, inducing membrane lipid peroxidation, and disrupting mitochondrial function, thereby disrupting the membrane system and reducing cell viability. Moreover, antofine treatment downregulated most differentially expressed proteins involved in carbon metabolism, pyruvate metabolism, and the tricarboxylic acid cycle (TCA) in P. italicum mycelia, which may explain the mitochondrial decomposition observed by TEM and the declines in ATP levels as well as the activities of TCA-related enzymes. These results indicate that antofine treatment inhibited P. italicum growth by targeting the cell membrane and mitochondria.

To characterise the regulation of abscisic acid (ABA) signal transduction during fruit development and ripening, we investigated the key genes involved in the ABA signalling pathway in kiwifruit (Actinidia chinensis), including 18 AcPYLs genes encoding ABA receptors, 7 AcPP2Cs genes encoding type 2C protein phosphatases, and 7 AcSnRK2s genes encoding members of the SNF1-related protein kinases 2 family identified in the kiwifruit reference genome. AcPYLs, AcPP2Cs, and AcSnRK2s from kiwifruit are putative homologues of the corresponding Arabidopsis and tomato proteins. Phylogenetic analysis revealed that AcPYLs and AcSnRK2s clustered into three subfamilies. Transcript levels indicated that the expression pattern of AcNCED4 was consistent with the ABA content of the pulp during kiwifruit development. Furthermore, the ABA content of the axile placenta was higher than that of the sarcocarp in kiwi pulp, and the expression of most ABA signal transduction genes, including AcPYLs, AcPP2Cs, and AcSnRK2s, was more predominant in the axile placenta. Moreover, AcPP2C3 was localised in the nucleus and could interact with all AcPYLs and AcSnRK2s in an ABA-independent manner, as revealed by subcellular localisation and yeast two-hybrid assays. These findings enhance our understanding of ABA signal transduction genes in kiwis, and provide the necessary background for further exploration of the molecular mechanisms at play during kiwifruit development.