Polygalacturonase Research Articles

Active packaging technology to retain storage quality of pear cv. “Bartlett” during shelf‐life periods under ambient holding after periodic cold storage

Response of “Bartlett” pears harvested at commercial maturity (104.29‐N firmness and 3.15 starch iodine rating) to various active packaging conditions using O2 (Fe powder) and ethylene (KMnO4) scavenger sachets in low‐density polyethylene (LDPE) film bags (25.4 and 50.8 μm), cold storage (2 ± 1°C with 95 ± 2%), and shelf‐life holding periods under ambient conditions (24 ± 3°C; 68 ± 5% relative humidity [RH]) was recorded as changes in physic chemical parameters. The fruits were packed in 25.4‐ and 50.8‐μm LDPE film bags containing 5%, 10%, and 15% Fe and KMnO4 powder incorporated on silica as inert carrier in form of sachets. After packaging the fruits airtight in film bags, they were placed in corrugated fiber board (CFB) boxes (29 × 23 × 14 cm; L × B × H). Fruits packed in 50.8‐μm LDPE film bags with sachets containing 15% Fe powder recorded maximum fruit firmness, total soluble solids (TSS), titratable acidity, and ascorbic acid with minimum spoilage, weight loss (physiological loss of weight [PLW]), pectin methylesterase (PME), polygalacturonase (PG) activity, and respiration rate and increase in fruit calcium content and highest level of overall acceptability (color, taste, aroma, and texture) after periodic cold storage and ambient shelf‐life periods. The effect of different treatments was compared by post hoc analysis using Tukey's test, which also revealed significant differences among different treatments. Our findings also revealed that pear fruit retains edible quality until fruit firmness > 30.89 N, TSS > 10.0%, and weight loss < 9.00%.

CHEMOINFORMATIC analysis ON SOME FUNGAL PECTINASES INHIBITORS

Abstract: Fusarium oxysporum f. sp. lycopersici attacks tomato plants and causes wilt disease. Fusarium Pathogenicity is including pectinases enzymes which enable the Fungal penetration into host cell wall. The present study is focused on using Computational tools such as Auto- Dock program for screening of inhibitors of endo and exopolygalacturonase enzymes.It based on Lamarckian Genetic Algorithm (LGA) that estimate the binding energy and inhibition constant as parameters to select the best binding.The binding energy and amino acids interactions for the selected inhibitors were compared with that of the enzyme substrate (polygalacturonic acid) Allium species such as onion plant have been used widely as antimicrobial and antifungal plants.It contains (up to 5% ) of non-protein sulfur amino-acids, including S-E-Prop-1-enyl-L-cysteine S-oxide, S-3-Allylsulphinyl-L-alanine and S-Methylcysteine sulfoxide have satisfactory binding interactions and inhibition constant with endo and exopolygalacturonase. In the present study, these compounds were extracted from white onion bulb Giza 20 and detected in the onion extract LC/MS analysis. The Inhibitory effect of these compounds for exopolygalacturonase enzyme was confirmed experimentally by determination of the enzyme activity in the presence and the absence of these compounds. White onion extract 45% inhibition percentage of the exopolygalacturonase activity.The enzyme kinetic study showed increase in the Km value with stable V-max value in presence of 7µg/µL of the onion extract.Also, In-vitro experiment of inhibition of F. oxysporum growth in presence 20% and 40% of onion extract showed inhibition percentages of 47% and 53% respectively The results concluded that onion extract inhibits Fusarium growth through inhibition of exo and endo polygalacturonase. The inhibitory effect of onion extract could be due to its contents of S-E-Prop-1-enyl-L-cysteine S-oxide, S-3-Allylsulphinyl-L-alanine and S-Methylcysteinesulphoxide, these compounds have excellent binding interactions and inhibition effects on both exo- and endo-polygalacturonases enzymes of Fusarium oxysporum f. sp. lycopersici Keywords: Chemoinformatic, Auto- Dock program,Fusarium oxysporum, Pectinases, exopolygalacturonase; Onion extract.

Paper-based colorimetric sensor for easy and simple detection of polygalacturonase activity aiming for diagnosis of Allium white rot disease

Polygalacturonase (PG) activity in plants can serve as an important index for plant disease. However, the conventional method to detect PG activity is a complex process and requires a skilled technician and expensive analytical equipment. In this study, a paper-based colorimetric sensor was developed based on the principle of the ruthenium red (RR) dye method for easy and simple measurement of PG activity. The proposed paper-based sensor has a three-layer structure for detection of PG activity in samples. The sensor sensitivity was enhanced by optimizing the pH of the sodium acetate buffer used in polygalacturonic acid (PGA)-RR complex formation and the reaction temperature for PG and the PGA-RR complex. Further, for quantitative analysis of PG activity, Delta RGB analysis was conducted to detect color changes in the sensing window of the sensor. Results presented that the linear measurement range of the paper sensor was 0.02–0.1 unit with the limit of detection of 0.02 unit, which showed a similar detection range, but a lower detection limit, compared to the spectrophotometry. Furthermore, PG activity based on culture condition was measured using samples from Sclerotium cepivorum to verify the potential application of the developed paper-based sensor in the field. The measured activity showed no statistically significant difference from the values obtained from the spectrophotometry at 95% confidence level. Therefore, the paper-based colorimetric sensor can be used to predict plant diseases in Allium crops during the stage of pathogen invasion, potentially contributing to the improvement of crop production.

Genome-Wide Identification and Expression Analysis of Polygalacturonase Gene Family in Kiwifruit (Actinidia chinensis) during Fruit Softening.

Polygalacturonase (PG) is an essential hydrolytic enzyme responsible for pectin degradation and thus plays an important role in fruit softening and other cell separation processes. PG protein is encoded by a multigene family, however, the members of PG gene family in kiwifruit (Actinidia chinensis) have not been extensively identified. In this study, a total of 51 AcPG genes in kiwifruit genome were identified. They are phylogenetically clustered into seven clades, and of them AcPG4 and AcPG18 with other known PG genes involved in fruit softening from peach, pear, papaya and melon form a small cluster together. The members of kiwifruit PG gene family consist of three to nine exons and two to eight introns, and their exon/intron structures are generally conserved in all clades except the clade D and E. During fruit softening of kiwifruit ‘Donghong’ under ambient temperature, cell wall modifying enzymes, including PG, PL (pectate and pectin lyases), and PE (pectinesterase, also known as pectin methylesterase, PME) showed a different activity profile, and of them, PG and PE activities largely correlated with the change of pectin content and firmness. Moreover, only 11 AcPG genes were highly or moderately expressed in softening fruit, and of which three AcPG genes (AcPG4, AcPG18, and AcPG8, especially the former two) has been found to strongly correlate with the profile of PG activity and pectin content, as well as fruit firmness, suggesting that they maybe play an important role in fruit softening. Thus, our findings not only benefit the functional characterization of kiwifruit PG genes, but also provide a subset of potential PG candidate genes for further genetic manipulation.

Changes in morphogenesis and carotenogenesis to influence polygalacturonase secretion in Aspergillus carbonarius mutant.

Mycelial morphogenesis and the production of fungal secretory proteins are still largely unknown. A mutant strain of Aspergillus carbonarius UV-10046 produced abundant polygalacturonase (PG) along with partially saturated canthaxanthin (PSC) at low pH conditions. In the present study, the relationship between PG secretion and PSC biosynthesis was studied using carotenogenic inhibitors and SDS-PAGE electrophoresis. Also the correlation between morphogenesis and PG secretion was investigated by analysing through microscopic studies. From the results, it was observed that secretion of PG was positively influenced by the PSC biosynthesis. The results also showed that the mutant with hairy mycelial structure resulted in higher PG activity when compared to the wild type that lacks hyper branching. From the results, it was confirmed that a mutation might have occurred in the isoprenoid pathway that has helped mutant for survival at acidic conditions. Further, an alteration in the morphogenesis and hyper branching development caused over secretion of PG enzyme in the mutant.

Transcriptomics and Proteomics Reveal the Cellulose and Pectin Metabolic Processes in the Tension Wood (Non-G-Layer) of Catalpa bungei.

Catalpa bungei is an economically important tree with high-quality wood and highly valuable to the study of wood formation. In this work, the xylem microstructure of C. bungei tension wood (TW) was observed, and we performed transcriptomics, proteomics and Raman spectroscopy of TW, opposite wood (OW) and normal wood (NW). The results showed that there was no obvious gelatinous layer (G-layer) in the TW of C. bungei and that the secondary wall deposition in the TW was reduced compared with that in the OW and NW. We found that most of the differentially expressed mRNAs and proteins were involved in carbohydrate polysaccharide synthesis. Raman spectroscopy results indicated that the cellulose and pectin content and pectin methylation in the TW were lower than those in the OW and NW, and many genes and proteins involved in the metabolic pathways of cellulose and pectin, such as galacturonosyltransferase (GAUT), polygalacturonase (PG), endoglucanase (CLE) and β-glucosidase (BGLU) genes, were significantly upregulated in TW. In addition, we found that the MYB2 transcription factor may regulate the pectin degradation genes PG1 and PG3, and ARF, ERF, SBP and MYB1 may be the key transcription factors regulating the synthesis and decomposition of cellulose. In contrast to previous studies on TW with a G-layer, our results revealed a change in metabolism in TW without a G-layer, and we inferred that the change in the pectin type, esterification and cellulose characteristics in the TW of C. bungei may contribute to high tensile stress. These results will enrich the understanding of the mechanism of TW formation.

ITRAQ-based quantitative proteomic analysis of peach fruit (Prunus persica L.) at different ripening and postharvest storage stages

Abstract To better understand the global and dynamic changes in peach (Prunus persica L. cv. Xiahui 8) fruit protein expression, an efficient and reliable proteomic technique, iTRAQ, was used to investigate peach fruit proteome from day -7 to day 8 during storage period at 25 ± 1 °C. A total of 387 proteins with more than 1.2-fold abundance changes were observed. These differentially expressed proteins (DEPs) are mainly related to 17 functional categories. DEPs in day -7 were mainly responsible for sugar and carbohydrate syntheses, protein translation, expression and modification, and maintenance of osmotic balance in high ion and material transport capacities and strong redox reaction environment. Harvesting induced the increase of (small) heat shock protein. Upon harvest, the increased level of respiration rates on day 4 reached the highest level. polygalacturonase (PG), pectase lyase (PL), pectinesterase (PE), chorismate mutase (CM), peptidyl-prolyl isomerase (PPIase) and phytoene synthase (PSY) showed increased abundances and reached a peak at day 6, which significantly positive correlation with 9-cis-epoxycarotenoid dioxygenase (NCED) protein, accelerated fruit softening and metabolism of protein, amino acid and lipid. The emergence of eukaryotic translation initiation factor 5A (EIF5A) on day 8 signified the intensification of apoptosis. Our study facilitated a comprehensive understanding of the complex proteomic reprograming and ripening-associated mechanisms that could be used for endeavors of breeding and postharvest processing to improve peach fruit quality.

Delay of ripening and softening in ‘Guifei’ mango fruit by postharvest application of melatonin

Abstract Melatonin (MT) functions as an important bio-active molecule in diverse physiological processes in higher plants. In the present study the role of MT in modulating ripening and softening in relation to ethylene and abscisic acid (ABA) biosyntheses in stored mango fruit was evaluated. The results showed that application of MT (0.5 mM, immersion for 1 h) to ‘Guifei’ mangoes effectively delayed the changes in ripening parameters including firmness, pulp color, β-carotene levels, soluble solids content (SSC), titratable acidity (TA) and respiration rate. MT markedly delayed climacteric ethylene production and 1-aminocyclopropane-1-carboxylic acid (ACC) levels in mango fruit during storage, likely a consequence of reduced activities of ACC synthase (ACS) and ACC oxidase (ACO). MT treatment resulted in delayed accumulation of ABA through reducing activity of a key ABA biosynthetic enzyme (9-cis-epoxycarotenoid dioxygenase, NCED). MT treatment suppressed the changes in activities of pectin-modifying enzymes including polygalacturonase (PG), β-galactosidase (β-Gal) and pectin methylesterase (PME), and limited the solubilization and depolymerization of pectin polysaccharides. The results indicate that MT could be involved in modulation of ripening and softening in mango fruit through inhibiting the biosyntheses of ethylene and ABA.

Novel biotechnological strategies to combat biotic stresses: polygalacturonase inhibitor (PGIP) proteins as a promising comprehensive option.

Global climate change and combinatorial environmental stresses pose grave challenges to food security and agricultural sustainability. This calls for diverse and futuristic approaches for the development of crops with increased resilience to natural vagaries. Though innumerable strategies involving diverse genes/pathways are being deciphered in plants to aid stress mitigation, the hunt is still on. Furthermore, strategies that work to alleviate a combination of stresses are always pertinent. In this review, we discuss polygalacturonase inhibitor (PGIP) proteins as a plausible option to mitigate multiple biotic stresses. These are ubiquitous cell wall proteins that inhibit the pectin-depolymerizing activity of cell wall loosening enzymes, polygalacturonases (PGs). While plant PGs are those responsible for developmental activities like fruit ripening, pollen tube elongation, etc., PGs from various biotic stress factors like insects, fungal and bacterial pathogens aid in invasion by reducing the plant cell wall rigidity. To counteract, plants secrete PGIPs, which inhibit the pectin hydrolyzing activity of PGs from the attacking pests and pathogens. Multiple approaches in diverse crop species have demonstrated PGIP-based protection against pathogens and insect pests. Additionally, effectual interaction between PGs-PGIP is an important aspect for successful utilization of this approach. Molecular strategies leading to improved PG-PGIPs interaction is a highlight to demonstrate the use of PGIPs as an amenable stress mitigation approach. The review focuses on a comprehensive update on phylogeny of PGIPs, natural variation of resistance as well as their emerging translational utility towards mitigation of various biotic stresses.

Transcriptome Analysis Unravels Metabolic and Molecular Pathways Related to Fruit Sac Granulation in a Late-Ripening Navel Orange (Citrus sinensis Osbeck).

Lanelate navel orange (Citrus sinensis Osbeck) is a late-ripening citrus cultivar increasingly planted in China. The physiological disorder juice sac granulation often occurs in the fruit before harvest, but the physiological and molecular mechanisms underlying this disorder remain elusive. In this study, we found that fruit granulation of the late-ripening navel orange in the Three Gorges area is mainly caused by the low winter temperature in high altitude areas. Besides, dynamic changes of water content in the fruit after freezing were clarified. The granulation of fruit juice sacs resulted in increases in cell wall cellulose and decreases in soluble solid content, and the cells gradually became shrivelled and hollow. Meanwhile, the contents of pectin, cellulose, and lignin in juice sac increased with increasing degrees of fruit granulation. The activities of pectin methylesterase (PME) and the antioxidant enzymes peroxidase (POD), superoxide dismutase, and catalase increased, while those of polygalacturonase (PG) and cellulose (CL) decreased. Furthermore, a total of 903 differentially expressed genes were identified in the granulated fruit as compared with non-disordered fruit using RNA-sequencing, most of which were enriched in nine metabolic pathways, and qRT-PCR results suggested that the juice sac granulation is closely related to cell wall metabolism. In addition, the expression of PME involved in pectin decomposition was up-regulated, while that of PG was down-regulated. Phenylalanine ammonia lyase (PAL), cinnamol dehydrogenase (CAD), and POD related to lignin synthesis were up-regulated, while CL involved in cellulose decomposition was down-regulated. The expression patterns of these genes were in line with those observed in low-temperature treatment as revealed by qRT-PCR, further confirming that low winter temperature is associated with the fruit granulation of late-ripening citrus. Accordingly, low temperature would aggravate the granulation by affecting cell wall metabolism of late-ripening citrus fruit.

Molecular Cloning and Characterization of an Acidic Polygalacturonase from Grapes and Its Potential in Industry.

Pectinase enzymes from different plants have many possible biotechnological applications in various industries. Considering industrial significance of pectinolytic enzymes, the polygalacturonase (PG) gene from grapes was cloned into Escherichia coli DH5α using pTZ57R/T vector. Homologous sequences established a close link to Vitis vinifera. Conserve domain analysis predicted PLN02218 domain belongs to the cl31843 superfamily, showing its function as polygalacturonase. After confirmation by PCR and restriction analysis, the PG gene was expressed in E. coli BL21 and induced by IPTG. Expression level was assessed by 12% SDS-PAGE, which showed a 47 kDa protein. High expression level in the soluble fraction indicated that the protein is intracellular or transmembrane. Maximum expression was obtained with 1 mM IPTG and 6 hour induction time, and autoinduction with lactose increased production of the recombinant enzyme. Zymogram analysis revealed that the induced protein was an active enzyme. Expressed PG showed pectinolytic effect on the physiochemical properties of lemon juice. Natural biopolymers are greatly needed because synthetic fibers can negatively affect health. Pectin hydrolysis of banana pseudostem by the PG enzyme produced better quality fiber. Morphological studies by scanning electron microscopy revealed pectin degradation within the fiber cell architecture, showing the effectiveness of PG treatment on banana pseudostem.

An insight into molecular interaction of PGIP with PG for banana cultivar.

PolyGalacturonase Inhibiting Proteins (PGIPs) are leucine rich repeat pathogenesis-related (PR) cell wall proteins, which interact and inhibit the PolyGalacturonase (PG), an enzyme secreted by the pathogen to degrade pectin. Interaction of PGIP with PG limits the vulnerability of PG by the activation of host defense response against pathogenic attack. Erwinia is gram-negative soft rot bacteria responsible for rhizome rot disease in banana and many other crop plants. The interaction of PG with PGIP is one of the crucial steps for plant-pathogen interaction. To study the molecular mechanism of PR proteins, we employed molecular modelling, protein-protein docking and molecular dynamics simulations of banana PGIP (bPGIP) with Erwinia carotovora PG (ecPG). Further, insilico site-directed mutagenesis was performed in Phaseolus vulgaris PGIP (pvPGIP2) to elucidate the interaction with ecPG. Docking and simulation studies divulge that binding of bPGIP and PvPGIP2 with active site residues of EcPG induces structural changes and thereby inhibit the enzyme. This study provides a unique insight into PG-PGIP interaction, which may help in the development of bacterial soft-rot resistant banana cultivars.

Purification and Thermodynamic Characteristics of an Exo-Polygalacturonase from Trichoderma Pseudokoningii

Polygalacturonases (PGs) are necessary to degrade the insoluble viscous pectin components during the clarification process of fruit juice and are produced by some plants and various microbes, such as bacteria, yeasts and fungi. In this study, an exo-polygalacturonase (exo-PGP4a) was purified from T. Pseudokoningii using DEAE-Sepharose and Sephacryl S-200 columns. We show that the enzyme produced in this study by solid-state fermentation of citrus Orange peel was purified 20-fold with 12.8% recovery. The apparent molecular mass of the enzyme was determined to be 25 kDa using gel filtration and SDS-PAGE. The optimum temperature and pH of the exo-PGP4a were 45and#176;C and 6, respectively. The exo-PGP4a showed half-lives of 50.95 and 21.32 min at 55 and 75and#176;C, respectively. The activation energy for denaturation (Ea*) was 42.596 kJ/mol. The Km value of the enzyme for PGA hydrolysis was 2 mg/ml, and the Vmax was 3.27 and#181;mol min-1 mg-1. Several metal cations, such as Cu2+and Zn2+, were found to enhance the enzymatic activity of the exo-PGP4a, while Pb2+, Ca2+, Ni2+, Cd2+, Co2+ and Hg2+ ions were found to be inhibitory. In this study, we suggest the exo-polygalacturonase has potential role of the clarification of Orange, Apple, Grape, and Peach juices in the food industry.

Microbial synergy between Pichia kudriazevii YS201 and Bacillus subtilis BS38 improves pulp degradation and aroma production in cocoa pulp simulation medium

Interactions between two major microorganisms from Ivorian cocoa fermentation, namely Bacillus subtilis BS38 and Pichia kudriazevii YS201, were investigated during fermentation in cocoa pulp simulation medium. The strains were mutually inhibitory, with Bacillus being more susceptible to this antagonistic effect than Pichia. However, both strains yielded different pulp-degrading enzymes, namely polygalacturonase (PG) from Pichia and pectate lyase (Pel) from Bacillus, that cooperate to efficiently breakdown pectin and vegetable pulp. The quantification of aromas from microbial cultures using Gas Chromatography-Mass Spectroscopy (GC-MS) coupled with headspace microextration (SPME) method, showed that P. kudriazevii produce mainly alcohols such as ethanol (63.165 g/L), phenylethanol (1.005 g/L), methylbutanol (0.138 g/L) and esters, notably ethyl acetate (0.037 g/L) and isoamyl acetate (0.032 g/L). The volatile fraction produced by Bacillus was dominated by butanediol (5.707 g/L), acetoin (1.933 g/L), phenylethanol (0.035 g/L) and acetic acid (0.034 g/L). In co-culture, Bacillus produced low levels of aroma compounds whereas a moderate decrease in the production of these compounds was observed in the yeasts strain. Thus, the dominant aromas present in the co-culture were mainly those from the yeasts strain; however, a 1.37 fold increase of ethanol production was observed in co-culture indicating a synergy between the strains. This study showed that cooperation between B. subtilis BS38 and P. kudriazevii YS201 leads principally to increasing pulp degradation and ethanol production, known as desirable properties for a well processing of cocoa fermentation.

Purification and Thermodynamic Characteristics of an Exo-Polygalacturonase from Trichoderma Pseudokoningii

Polygalacturonases (PGs) are necessary to degrade the insoluble viscous pectin components during the clarification process of fruit juice and are produced by some plants and various microbes, such as bacteria, yeasts and fungi. In this study, an exo-polygalacturonase (exo-PGP4a) was purified from T. Pseudokoningii using DEAE-Sepharose and Sephacryl S-200 columns. We show that the enzyme produced in this study by solid-state fermentation of citrus Orange peel was purified 20-fold with 12.8% recovery. The apparent molecular mass of the enzyme was determined to be 25 kDa using gel filtration and SDS-PAGE. The optimum temperature and pH of the exo-PGP4a were 45and#176;C and 6, respectively. The exo-PGP4a showed half-lives of 50.95 and 21.32 min at 55 and 75and#176;C, respectively. The activation energy for denaturation (Ea*) was 42.596 kJ/mol. The Km value of the enzyme for PGA hydrolysis was 2 mg/ml, and the Vmax was 3.27 and#181;mol min-1 mg-1. Several metal cations, such as Cu2+and Zn2+, were found to enhance the enzymatic activity of the exo-PGP4a, while Pb2+, Ca2+, Ni2+, Cd2+, Co2+ and Hg2+ ions were found to be inhibitory. In this study, we suggest the exo-polygalacturonase has potential role of the clarification of Orange, Apple, Grape, and Peach juices in the food industry.

OsPGIP1-Mediated Resistance to Bacterial Leaf Streak in Rice is Beyond Responsive to the Polygalacturonase of Xanthomonas oryzae pv. oryzicola

Polygalacturonase-inhibiting proteins (PGIPs) have been shown to recognize fungal polygalacturonases (PGs), which initiate innate immunity in various plant species. Notably, the connection between rice OsPGIPs and PGs in Xanthomonas oryzae pv. oryzicola (Xoc), which causes bacterial leaf streak (BLS), remains unclear. Here, we show that OsPGIP1 was strongly induced after inoculating rice with the Xoc strain RS105. Furthermore, OsPGIP1-overexpressing (OV) and RNA interference (RNAi) rice lines increased and decreased, respectively, the resistance of rice to RS105, indicating that OsPGIP1 contributes to BLS resistance. Subsequently, we generated the unique PG mutant RS105Δpg, the virulence of which is attenuated compared to that of RS105. Surprisingly, the lesion lengths caused by RS105Δpg were similar to those caused by RS105 in the OV lines compared with wild-type ZH11 with reduced Xoc susceptibility. However, the lesion lengths caused by RS105Δpg were still significantly shorter in the OV lines than in ZH11, implying that OsPGIP1-mediated BLS resistance could respond to other virulence factors in addition to PGs. To explore the OsPGIP1-mediated resistance, RNA-seq analysis were performed and showed that many plant cell wall-associated genes and several MYB transcription factor genes were specifically expressed or more highly induced in the OV lines compared to ZH11 postinoculation with RS105. Consistent with the expression of the differentially expressed genes, the OV plants accumulated a higher content of jasmonic acid (JA) than ZH11 postinoculation with RS105, suggesting that the OsPGIP1-mediated resistance to BLS is mainly dependent on the plant cell wall-associated immunity and the JA signaling pathway.

Ethylene plays an important role in the softening and sucrose metabolism of blueberries postharvest

We studied the effects of ethylene on softening and sucrose metabolism in postharvest blueberry fruit by examining the responses of fruit firmness, cell wall polysaccharides, cell wall enzymes, four key genes of cell wall degradation and metabolism, enzyme activities, and five key genes of sucrose metabolism to exogenous ethylene treatments. Ethylene was found to accelerate blueberry softening, as it promoted the degradation of pectin and expression of pectinesterase (PE) and polygalacturonase (PG). Sucrose catabolism was accelerated with fruit softening, while sucrose content, sucrose phosphate synthase (SPS) activity were positively correlated with the loss of fruit firmness. Exogenous ethylene treatments promoted sucrose metabolism by inhibiting the expression of VcSPS1 and VcNIN2 and stimulating the expression of VcSS1 and VcCWINV1. These results indicate that ethylene plays an important role in fruit softening and sucrose metabolism of blueberry at 20 °C, and there may be a link between sucrose metabolism and fruit softening.

Ethylene insensitive3-like2 (OsEIL2) confers stress sensitivity by regulating OsBURP16, the β subunit of polygalacturonase (PG1β-like) subfamily gene in rice

The transcription factors EIN3 (ETHYLENE-INSENSITIVE 3) and EILs (EIN3-Likes) play important roles in plant development and defense responses; however, their mechanism in these processes remain unclear. Here, we report that OsEIL2, an EIN3-like transcription factor from rice (Oryza sativa), plays important roles in abiotic stress and leaf senescence. OsEIL2 is a nuclear-localized protein with transactivation activity in the C-terminus (amino acids 344–583) and can be induced by NaCl, polyethylene glycol (PEG), dark, and abscisic acid (ABA) treatment. Transgenic plants of overexpressing OsEIL2 (OsEIL2-OX) show reduced tolerance to salt and drought stress compared with the controls. While the transgenic plants of overexpressing OsEIL2-RNA interference (OsEIL2-RNAi) exhibit enhanced tolerance to salt and drought stress compared with the controls. Moreover, seedlings of OsEIL2-overexpressing transgenic plants exhibit delayed leaf development and an accelerated dark-induced senescence phenotype, whereas OsEIL2-RNAi plants display the opposite phenotype. We further found that OsEIL2 functions upstream of OsBURP14 and OsBURP16. OsBURP14 and OsBURP16 are the members of the β subunit of polygalacturonase subfamilies. OsBURP16 overexpression reduced pectin content and cell adhesion and increased abiotic stress sensitivity in rice. OsEIL2 binds directly to the promoter of OsBURP14 and OsBURP16 and activates their transcript levels. We also found that OsEIL2 overexpression decreased the pectin content by increasing polygalacturonase (PG) activity. Taken together, these results revealed a new mechanism of OsEIL2 in abiotic stress responses. These findings provide new insights into plant resistance to abiotic stress.

A second VrPGIP1 allele is associated with bruchid resistance (Callosobruchus spp.) in wild mungbean (Vigna radiata var. sublobata) accession ACC41.

Two bruchid species, azuki bean weevil (Callosobruchus chinensis L.) and cowpea weevil (Callosobruchus maculatus F.), are the most important insect pests of mungbean [Vigna radiata (L.) Wilczek] after harvest. Improving bruchid resistance is a major goal for mungbean breeders. Bruchid resistance in mungbean is controlled by a single major locus, Br. The tightly linked VrPGIP1 and VrPGIP2, which encode polygalacturonase-inhibiting proteins (PGIPs), are the candidategenes at the Br locus associated with bruchid resistance. One VrPGIP1 resistance allele and two VrPGIP2 resistance alleles have been identified. In this study, we fine-mapped the bruchid-resistance genes in wild mungbean (V. radiata var. sublobata) accession ACC41 using the F2 population (574 individuals) derived from the 'Kamphaeng Saen 2' (susceptible) × ACC41 (resistant) cross. A QTL analysis indicated that the resistance to the azuki bean weevil and cowpea weevil in ACC41 is controlled by a major QTL (qBr5.1) and a minor QTL (qBr5.2), which are only 0.3cM apart. qBr5.1 and qBr5.2 accounted for about 82% and 2% of the resistance variation in the F2 population, respectively. qBr5.1 was mapped to a 237.35-kb region on mungbean chromosome 5 containing eight annotated genes, including VrPGIP1 and VrPGIP2. An examination of the ACC41 VrPGIP1 and VrPGIP2 sequences revealed a new allele for VrPGIP1 (i.e., VrPGIP1-2). Compared with the wild-type sequence, VrPGIP1-2 has five SNPs, of which four cause amino acid changes (residues 125, 129, 188, and 336). A protein sequence analysis indicated that residues 125 and 129 in VrPGIP1-2 are in a β-sheet B1 region, whereas residues 188 and 336 are in a C10-helix region and at the end of the C-terminal region, respectively. Because the β-sheet B1 region is important for interactions with polygalacturonase (PG), residues 125 and 129 in VrPGIP1-2 likely contribute to bruchid resistance by inhibiting PG. Our results imply that VrPGIP1-2 is associated with the bruchid resistance of wild mungbean accession ACC41. This new resistance allele may be useful for breeding mungbean varieties exhibiting durable bruchid resistance.

Changes in activity of polygalacturonase (PG), pectinesterase (PE) and cellulase (Cx) in pulp during fruit development of two ripening Jujube Ziziphus spp. cultivars

The activities of polygalacturonase (PG), pectinesterase (PE) and cellulase (Cx) were investigated in two jujube cultivars (Zatoni and Bambawi) during fruit development, The jujube fruit Zatwni and Bambawi cvs, displayed a double sigmoidal growth curve with very short stage II (2 weeks in Zatwni and 4 weeks in Bambawi cv.). the pectin content was high during early stage of fruit development, but declined gradually with fruit development and reached their lowest value when the fruit entered the ripening phase. The PG, PE and Cx were low level during early stages of fruit development, but there were rapid increase in these enzymes activity as the jujube entered variation stage, and maturity phase.