Purification and characterization of isoforms of beta-galactosidases in mung bean seedlings

NIR-excited imaging and in vivo visualization of β-galactosidase activity using a pyranonitrile-modified upconversion nanoprobe

β-galactosidase (β-gal) is a diagnostic biomarker of primary ovarian cancers. The development of effective fluorescent probes for investigating the activity of β-gal will be beneficial to cancer diagnosis. Herein, a near-infrared (NIR) excited ratiometric nanoprobe (DCM-β-gal-UCNPs) by assembling pyranonitrile dye (DCM-β-gal) on the surface of upconversion nanophosphors (UCNPs) was designed for the evaluation of β-gal activity in vivo. Upon the interaction with β-gal, a marked decrease of upconversion luminescence (UCL) signal in the green channel was observed owing to the luminescence resonance energy transfer from the UCNPs to pyranonitrile chromophore, whereas the NIR UCL emission at 800 nm was almost no influence. Thus, the β-gal activity could be quantitatively detected by the UCL intensity ratio of UCL_{543 nm}/UCL_{800 nm} with the limit of detection of 3.1 × 10^-4 U/mL. Moreover, DCM-β-gal-UCNPs was effectively applied for monitoring β-gal fluctuation in living cells and zebrafish by a ratiometric UCL signal excited by 980 nm laser. We envision that nanoprobe DCM-β-gal-UCNPs might be used as a potential bioimaging tool to disclose more biological information of β-gal in β-gal-associated diseases in the future.

Kinetic and thermodynamic studies of novel acid phosphatase isolated and purified from Carthamus oxyacantha seedlings

Acid phosphatase (ACP) is a key enzyme in the regulation of phosphate feeding in plants. In this study, a new ACP from C. oxyacantha was isolated to homogeneity and biochemically described for the first time. Specific activity (283 nkat/mg) was found after 2573 times purification fold and (17 %) yield. Using SDS-PAGE under denaturing and nondenaturing conditions, ACP was isolated as a monomer with a molecular weight of 36 kDa. LC-MS/MS confirmed the presence of this band, suggesting that C. oxycantha ACP is a monomer. The enzyme could also hydrolyze orthophosphate monoester with an optimal pH of 5.0 and a temperature of 50 °C. Thermodynamic parameters were also determined (Ea, ΔH°, ΔG°, and ΔS°). ACP activity was further studied in the presence of cysteine, DTT, SDS, EDTA, β-ME, Triton-X-100 H₂O₂, and PMSF. The enzyme had a K_m of 0.167 mM and an Ea of 9 kcal/mol for p-nitrophenyl phosphate. The biochemical properties of the C. oxyacantha enzyme distinguish it from other plant acid phosphatases and give a basic understanding of ACP in C. oxyacantha. The results of this investigation also advance our knowledge about the biochemical significance of ACP in C. oxyacantha. Thermal stability over a wide pH and temperature range make it more suitable for use in harsh industrial environments. However, further structural and physiological studies are anticipated to completely comprehend its important aspects in oxyacantha species.

Identification, kinetics and thermodynamic analysis of novel β-galactosidase from Convolvulus arvensis seeds: An efficient agent for delactosed milk activity

The β-galactosidase was extracted and purified from 100 g of C. arvensis seeds using a variety of protein purification procedures such as ammonium sulphate fractionation, gel filtration, and finally chromatography on a cationic ion exchanger. The effects of metal ions, kinetics parameters, and glycoprotein nature were determined, as well as the optimal pH and temperature of the purified enzyme. With a high specific activity (72 units/mg), β-galactosidase was isolated to a 24-fold apparent electrophoretic homogeneity. The molecular mass of β-galactosidase was determined as monomeric, which was further confirmed by SDS-PAGE and MALDI-TOF/MS analysis, with a 45 kDa molecular weight. The enzyme has a K_m of 0.33 mM and a V_max of 42 μmol/min Lactose in milk was reduced by 38.5 and 70 % after 4 h of incubation with β-galactosidase from C. arvensis. The β-galactosidase thermal inactivation kinetic parameters ΔH°, ΔS°, and ΔG° were calculated, indicating that the enzyme undergoes significant unfolding events during denaturation. Using β-galactosidase from C. arvensis seeds, lactose hydrolysis in milk up to approx. 50 % was observed. The findings indicate the potential use of C. arvensis seeds for the production of low/delactosed milk for lactose-intolerant population.

Genetic loci associated with freezing tolerance in a European rapeseed (Brassica napus L.) diversity panel identified by genome-wide association mapping

Winter biotypes of rapeseed (Brassica napus L.) require a vernalization treatment to enter the reproductive phase and generally produce greater yields than spring rapeseed. To find genetic loci associated with freezing tolerance in rapeseed, we first performed genotyping-by-sequencing (GBS) on a diversity panel consisting of 222 rapeseed accessions originating primarily from Europe, which identified 69,554 high-quality single-nucleotide polymorphisms (SNPs). Model-based cluster analysis suggested that there were eight subgroups. The diversity panel was then phenotyped for freezing survival (visual damage and Fv/Fo and Fv/Fm) after 2 months of cold acclimation (5°C) and a freezing treatment (-15°C for 4 h). The genotypic and phenotypic data for each accession in the rapeseed diversity panel was then used to conduct a genome-wide association study (GWAS). GWAS results showed that 14 significant markers were mapped to seven chromosomes for the phenotypes scored. Twenty-four candidate genes located within the mapped loci were identified as previously associated with lipid, photosynthesis, flowering, ubiquitination, and cytochrome P450 in rapeseed or other plant species.

Characterization of β-galactosidase and α-galactosidase activities from the halophilic bacterium Gracilibacillus dipsosauri

Purpose

Gracilibacillus dipsosauri strain DD1 is a salt-tolerant Gram-positive bacterium that can hydrolyze the synthetic substrates o-nitrophenyl-β-d-galactopyranoside (β-ONP-galactose) and p-nitrophenyl-α-d-galactopyranoside (α-PNP-galactose). The goals of this project were to characterize the enzymes responsible for these activities and to identify the genes encoding them.

Methods

G. dipsosauri strain DD1 was grown in tryptic soy broth containing various carbohydrates at 37 °C with aeration. Enzyme activities in cell extracts and whole cells were measured colorimetrically by hydrolysis of synthetic substrates containing nitrophenyl moieties. Two enzymes with β-galactosidase activity and one with α-galactosidase activity were partially purified by ammonium sulfate fractionation, ion-exchange chromatography, and gel-filtration chromatography from G. dipsosauri. Coomassie Blue-stained bands corresponding to each activity were excised from nondenaturing polyacrylamide gels and subjected to peptide sequencing after trypsin digestion and HPLC/MS analysis.

Result

Formation of β-galactosidase and α-galactosidase activities was repressed by d-glucose and not induced by lactose or d-melibiose. β-Galactosidase I had hydrolytic and transgalactosylation activity with lactose as the substrate but β-galactosidase II showed no activity towards lactose. The α-galactosidase had hydrolytic and transgalactosylation activity with d-melibiose but not with d-raffinose. β-Galactosidase I had a lower Km with β-ONP-galactose as the substrate (0.693 mmol l−1) than β-galactosidase II (1.662 mmol l−1), was active at more alkaline pH, and was inhibited by the product d-galactose. β-Galactosidase II was active at more acidic pH, was partially inhibited by ammonium salts, and showed higher activity with α-PNP-arabinose as a substrate. The α-galactosidase had a low Km with α-PNP-galactose as the substrate (0.338 mmol l−1), a pH optimum of about 7, and was inhibited by chloride-containing salts. β-Galactosidase I activity was found to be due to the protein A0A317L6F0 (encoded by gene DLJ74_04930), β-galactosidase II activity to the protein A0A317KZG3 (encoded by gene DLJ74_12640), and the α-galactosidase activity to the protein A0A317KU47 (encoded by gene DLJ74_17745).

Conclusions

G. dipsosauri forms three intracellular enzymes with different physiological properties which are responsible for the hydrolysis of β-ONP-galactose and α-PNP-galactose. BLAST analysis indicated that similar β-galactosidases may be formed by G. ureilyticus, G. orientalis, and G. kekensis and similar α-galactosidases by these bacteria and G. halophilus.

Identification of Key Metabolic Pathways and Biomarkers Underlying Flowering Time of Guar (Cyamopsis tetragonoloba (L.) Taub.) via Integrated Transcriptome-Metabolome Analysis

Guar (Cyamopsis tetragonoloba (L.) Taub.) is an annual legume crop native to India and Pakistan. Seeds of the plant serve as a source of galactomannan polysaccharide (guar gum) used in the food industry as a stabilizer (E412) and as a gelling agent in oil and gas fracturing fluids. There were several attempts to introduce this crop to countries of more northern latitudes. However, guar is a plant of a short photoperiod, therefore, its introduction, for example, to Russia is complicated by a long day length during the growing season. Breeding of new guar varieties insensitive to photoperiod slowed down due to the lack of information on functional molecular markers, which, in turn, requires information on guar genome. Modern breeding strategies, e.g., genomic predictions, benefit from integration of multi-omics approaches such as transcriptome, proteome and metabolome assays. Here we present an attempt to use transcriptome-metabolome integration to understand the genetic determination of flowering time variation among guar plants that differ in their photoperiod sensitivity. This study was performed on nine early- and six delayed-flowering guar varieties with the goal to find a connection between 63 metabolites and 1,067 differentially expressed transcripts using Shiny GAM approach. For the key biomarker of flowering in guar myo-inositol we also evaluated the KEGG biochemical pathway maps available for Arabidopsis thaliana. We found that the phosphatidylinositol signaling pathway is initiated in guar plants that are ready for flowering through the activation of the phospholipase C (PLC) gene, resulting in an exponential increase in the amount of myo-inositol in its free form observed on GC-MS chromatograms. The signaling pathway is performed by suppression of myo-inositol phosphate kinases (phosphorylation) and alternative overexpression of phosphatases (dephosphorylation). Our study suggests that metabolome and transcriptome information taken together, provide valuable information about biomarkers that can be used as a tool for marker-assisted breeding, metabolomics and functional genomics of this important legume crop.

A near-infrared fluorescent probe for monitoring and imaging of β-galactosidase in living cells

β-Galactosidase (β-gal) which is overexpressed in primary ovarian cancer can be employed as a valuable biomarker for ovarian cancer. Thus, monitoring and imaging endogenous β-gal in living cells is of great importance. Herein, a dicyanoisophorone-based near-infrared (NIR) fluorescent probe 2-(5,5-dimethyl-3-((E)-4-(((2R,3S,4R,5S,6S)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)styryl)cyclohex-2-en-1-ylidene)malononitrile named DP-βgal, was rationally designed and synthesized for the monitoring of β-gal activity in living cells. In the presence of β-gal, with the breaking of the glycosidic bond, the NIR fluorescence of the dicyanoisophorone derivative gradually recovered, enabling the fluorescence "off-on" quantitative determination of β-gal activity. DP-βgal has the advantages of good selectivity and high sensitivity for the detection of β-gal, with the limit of detection (LOD) of 3.2 × 10^-3 U. Furthermore, based on its advantages of long-wavelength emission and excellent biocompatibility, the practical applications of DP-βgal in NIR imaging of β-gal in living ovarian cancer cells (SKOV-3) were demonstrated.

Cell wall hydrolases act in concert during aerenchyma development in sugarcane roots

BACKGROUND AND AIMS

Cell wall disassembly occurs naturally in plants by the action of several glycosyl-hydrolases during different developmental processes such as lysigenous and constitutive aerenchyma formation in sugarcane roots. Wall degradation has been reported in aerenchyma development in different species, but little is known about the action of glycosyl-hydrolases in this process.

METHODS

In this work, gene expression, protein levels and enzymatic activity of cell wall hydrolases were assessed. Since aerenchyma formation is constitutive in sugarcane roots, they were assessed in segments corresponding to the first 5 cm from the root tip where aerenchyma develops.

KEY RESULTS

Our results indicate that the wall degradation starts with a partial attack on pectins (by acetyl esterases, endopolygalacturonases, β-galactosidases and α-arabinofuranosidases) followed by the action of β-glucan-/callose-hydrolysing enzymes. At the same time, there are modifications in arabinoxylan (by α-arabinofuranosidases), xyloglucan (by XTH), xyloglucan-cellulose interactions (by expansins) and partial hydrolysis of cellulose. Saccharification revealed that access to the cell wall varies among segments, consistent with an increase in recalcitrance and composite formation during aerenchyma development.

CONCLUSION

Our findings corroborate the hypothesis that hydrolases are synchronically synthesized, leading to cell wall modifications that are modulated by the fine structure of cell wall polymers during aerenchyma formation in the cortex of sugarcane roots.

Novel fluorescent probe for rapid and ratiometric detection of β-galactosidase and live cell imaging

β-Galactosidase (β-gal) is an important biomarker for primary ovarian cancers and cell senescence; however, a fast response fluorescent probe for ratiometric monitoring is still rare. A novel, ratiometric water-soluble fluorescent probe (FLM) for β-gal was developed. The emission ratio F₅₅₀/F₄₅₀ reached the maxima at about 5 min and can be used for real-time detection of β-gal; the ratio gained an ultimate enhancement of about 260-fold. The ratio (F₅₅₀/F₄₅₀) displayed brilliant β-gal-dependent performance and responded linearly with β-gal activity. The probe showed wonderful biocompatibility and was successfully used for the bioimaging of endogenous β-gal in the human ovarian cancer cell line OVCAR-3.

Ratiometric fluorescent probes with a self-immolative spacer for real-time detection of β-galactosidase and imaging in living cells

Ratiometric fluorescent probes with a self-immolative spacer for β-galactosidase (β-gal) were developed. They function by β-gal-cleaving the β-galactoside bond of fluorescent substrates, followed by self-immolation to liberate the amino group of fluorophore. Thus, a remarkable variation in the photophysical properties was observed and the corresponding ratiometric detection of β-gal was realized. Our studies demonstrated that the GNPN exhibited high sensitivity for recognition of β-gal, with a detection limit as low as 0.17 U L^-1. GNPN can rapidly quantify β-gal enzyme activity; the emission ratio F₅₄₅/F₄₇₅ for the GNPN reached maxima after approximately 4 min, which was one of the shortest response time ever reported. Furthermore, we demonstrated that these probes possess excellent biocompatibility and can be used to visualize the endogenous β-gal in ovarian cancer cells.

β-Galactosidase from Ginkgo biloba seeds active against β-galactose-containing N-glycans: purification and characterization

In this study, we purified an acidic β-galactosidase to homogeneity from Ginkgo biloba seeds (β-Gal’ase Gb-1) with approximately 270-fold purification. A molecular mass of the purified β-Gal’ase Gb-1 was estimated about 35 kDa by gel filtration and 32 kDa by SDS-PAGE under non-reducing condition, respectively. On the other hand, β-Gal’ase Gb-1 produced a single band with a molecular mass of 16 kDa by SDS-PAGE under reducing condition. The N-terminal amino acid sequences of 32 kDa and 16 kDa molecules were the same and identified as H-K-A-N-X-V-T-V-A-F-V-M-T-Q-H-, suggesting that β-Gal’ase Gb-1 may function as a homodimeric structure in vivo. When complex-type N-glycans containing β-galactosyl residues were used as substrates, β-Gal’ase Gb-1 showed substantial activity for β1-4 galactosyl residue and modest activity for β1-3 galactosyl residue with an optimum pH near 5.0. Based on these results, the involvement of β-Gal’ase Gb-1 in the degradation of plant complex-type N-glycans is discussed.

Enzymatic activity and substrate specificity of the recombinant tomato β-galactosidase 1

The open reading frame of tomato β-galactosidase 1 was expressed in yeast, and the enzymatic properties and substrate specificity were investigated. The enzyme had peak activity at pH 5.0 and 40-50°C. TBG1 was active on β-(1,3)- and β-(1,6)-galactobiose and lactose. TBG1 released galactose from lupin galactan, tomato fruit alkali soluble pectin, arabinogalactan, gum arabic and methyl β-(1,6)-galactohexaoside, but not from labeled β-(1,4)-galactoheptaose. TBG1 was assessed for its ability to degrade three galactosyl-containing cell wall fractions purified from different development and ripening stages of tomato fruit. TBG1 released galactose from all of the fractions from all of the stages tested. TBG1 activity was highest on the hemicellulose fraction at the 10 and 20d after pollination stage. This result is not correlated the with TBG1 expression pattern. TBG1 might act on a small but specific set of polysaccharide containing galactose.

Pepper β-Galactosidase 1 (PBG1) Plays a Significant Role in Fruit Ripening in Bell Pepper (Capsicum annuum)

During bell pepper (Capsicum annuum L.) fruit ripening, beta-galactosidase activity increased markedly as compared with other glycosidases. We purified 77.5 kDa exo-1,4-beta-D-galactanase from red bell pepper fruit classified as beta-galactosidase II. A marked decrease in galactose content appeared during fruit ripening, especially in the pectic fraction. The purified enzyme hydrolyzed a considerable amount of galactose residues in this fraction. We isolated bell pepper beta-galactosidase (PBG1) cDNA. This PBG1 protein contained the putative active site, G-G-P-[LIVM]-x-Q-x-E-N-E-[FY], belonging to glycosyl hydrolase family 35. Quantitative RT-PCR revealed that the expression of PBG1 in red fruit was significantly stronger than that from any other tissues. Moreover, expression of PBG1 occurred prior to that of pepper endo-polygalacturonase 1 (PPG1), the major fruit-ripening enzyme. Based on these results, it appears that the hydrolysis of galactose residues in pectic substances is the first event in the ripening process in bell pepper fruit.

An exo-β-(1→3)-D-galactanase from Streptomyces sp. provides insights into type II arabinogalactan structure

An exo-β-(1→3)-D-galactanase (SGalase1) that specifically cleaves the β-(1→3)-D-galactan backbone of arabinogalactan-proteins (AGPs) was isolated from culture filtrates of a soil Streptomyces sp. Internal peptide sequence information was used to clone and recombinantly express the gene in E. coli. The molecular mass of the isolated enzyme was ~45 kDa, similar to the 48.2 kDa mass predicted from the amino acid sequence. The pI, pH and temperature optima for the enzyme were ~7.45, 3.8 and 48 °C, respectively. The native and recombinant enzymes specifically hydrolysed β-(1→3)-D-galacto-oligo- or poly-saccharides from the upstream (non-reducing) end, typical of an exo-acting enzyme. A second homologous Streptomyces gene (SGalase2) was also cloned and expressed. SGalase2 was similar in size (47.9 kDa) and enzyme activity to SGalase1 but differed in its pH optimum (pH 5). Both SGalase1 and SGalase2 are predicted to belong to the CAZy glycosyl hydrolase family GH 43 based on activity, sequence homology and phylogenetic analysis. The K(m) and V(max) of the native exo-β-(1→3)-D-galactanase for de-arabinosylated gum arabic (dGA) were 19 mg/ml and 9.7 μmol D-Gal/min/mg protein, respectively. The activity of these enzymes is well suited for the study of type II galactan structures and provides an important tool for the investigation of the biological role of AGPs in plants. De-arabinosylated gum arabic (dGA) was used as a model to investigate the use of these enzymes in defining type II galactan structure. Exhaustive hydrolysis of dGA resulted in a limited number of oligosaccharide products with a trisaccharide of Gal(2)GlcA(1) predominating.

Distinct roles of β-galactosidase paralogues of the rumen bacterium Mannheimia succiniciproducens

Mannheimia succiniciproducens, a rumen bacterium belonging to the family Pasteurellaceae, has two putative β-galactosidase genes, bgaA and bgaB, encoding polypeptides whose deduced amino acid sequences share 56% identity with each other and show approximately 30% identity to the Escherichia coli gene for LacZ. The M. succiniciproducens bgaA (MsbgaA) gene-deletion mutant was not able to grow on lactose as the sole carbon source, suggesting its essential role in lactose metabolism, whereas the MsbgaB gene-deletion mutant did not show any growth defect on a lactose medium. Furthermore, the expression of the MsbgaA gene was induced by the addition of lactose in the growth medium, whereas the MsbgaB gene was constitutively expressed independently of a carbon source. Biochemical characterization of the recombinant proteins revealed that MsBgaA is more efficient than MsBgaB in hydrolyzing o-nitrophenyl-β-d-galactopyranoside and p-nitrophenyl-β-d-galactopyranoside. MsBgaA was highly specific for the hydrolysis of lactose, with a catalytic efficiency of 46.9 s(-1) mM(-1). However, MsBgaB was more efficient for the hydrolysis of lactulose than lactose, and the catalytic efficiency was 10.0 s(-1) mM(-1). Taken together, our results suggest that the β-galactosidase paralogues of M. succiniciproducens BgaA and BgaB play a critical role in lactose metabolism and in an unknown but likely specific function for rumen bacteria, respectively.

Study of gherkin lactase in cell culture and in seedlings

A synthetic substrate replacing lactose has facilitated application of a simple, rapid and sensitive method for the identification and determination of extracellular and intracellular gherkin lactase. The intracellular enzyme activity was estimated from the cell suspension, while the extracellular enzyme activity was established within the cell free cultivation medium. A suspension of gherkin cells was permeabilized by Tween 20, or Tween 80, or hexadecyltrimethyl ammonium bromide, or hexadecylpyridinium chloride or ethanol added one at a time and then immobilized by glutaraldehyde. The highest lactase activity was at pH 4.8 at a temperature of 55°C. The hydrolysis of substrate was linear for 4.5h and reached 60% conversion. The cells had high lactase activity and good stability. During long-term storage they demonstrated convenient physico-mechanical properties.

Fine mapping a QTL qCTB7 for cold tolerance at the booting stage on rice chromosome 7 using a near-isogenic line

Low temperature at the booting stage is a serious abiotic stress in rice, and cold tolerance is a complex trait controlled by many quantitative trait loci (QTL). A QTL for cold tolerance at the booting stage in cold-tolerant near-isogenic rice line ZL1929-4 was analyzed. A total of 647 simple sequence repeat (SSR) markers distributed across 12 chromosomes were used to survey for polymorphisms between ZL1929-4 and the cold-sensitive japonica cultivar Towada, and nine were polymorphic. Single marker analysis revealed that markers on chromosome 7 were associated with cold tolerance. By interval mapping using an F(2) population from ZL1929-4 x Towada, a QTL for cold tolerance was detected on the long arm of chromosome 7. The QTL explained 9 and 21% of the phenotypic variances in the F(2) and F(3) generations, respectively. Recombinant plants were screened for two flanking markers, RM182 and RM1132, in an F(2) population with 2,810 plants. Two-step substitution mapping suggested that the QTL was located in a 92-kb interval between markers RI02905 and RM21862. This interval was present in BAC clone AP003804. We designated the QTL as qCTB7 (quantitative trait locus for cold tolerance at the booting stage on chromosome 7), and identified 12 putative candidate genes.

Comparative characterization of the Arabidopsis subfamily a1 beta-galactosidases

The Arabidopsis genome contains 17 predicted beta-galactosidase genes, all of which belong to glycosyl hydrolase (GH) Family 35. These genes have been further grouped into seven subfamilies based on sequence similarity. The largest of these, subfamily a1, consists of six genes, Gal-1 (At3g13750), Gal-2 (At3g52840), Gal-3 (At4g36360), Gal-4 (At5g56870), Gal-5 (At1g45130), and Gal-12 (At4g26140), some of which were characterized in previous studies. We report here the purification and biochemical characterization of recombinant Gal-1, Gal-3, Gal-4 and Gal-12 from Pichiapastoris, completing the analysis of all six recombinant proteins, as well as the isolation and characterization of the native Gal-2 protein from Arabidopsis leaves. Comparison of the relative expression levels of the subfamily a1 beta-galactosidases at the mRNA and protein levels uncovered evidence of differential regulation, which may involve post-transcriptional and post-translational processes. In addition, this study provides further support for the proposed function of the subfamily a1 beta-galactosidases in cell wall modification based on analysis of the organ-specific expression and subcellular localization of Gal-1 and Gal-12. Our study suggests that, despite some differences in individual biochemical characteristics and expression patterns, each member of the family has the potential to contribute to the dynamics of the Arabidopsis plant cell wall.

A beta-galactosidase from pea seeds (PsBGAL): purification, stabilization, catalytic energetics, conformational heterogeneity, and its significance

A basic glycosylated beta-galactosidase (PsBGAL) has been purified from pea seeds by 910-fold with a specific activity of 77.33 mumoL min(-1) mg(-1) protein. The purified enzyme is an electrophoretically homogeneous protein consisting of a single protein band with an apparent M(r) of 55 kDa, while the deglycosylated enzyme has a M(r) of 54.2 kDa on SDS-PAGE under reducing conditions. According to MALDI-TOF measurements of the 55 kDa band, the enzyme showed a homology with BGAL from other sources present in the SWISS-PROT database, while it showed no resemblance to any lectin. The N-terminal sequence of PsBGAL was determined as TIECK and showed a resemblance to BGAL from Arabidopsis thaliana (Q93Z24). The enzyme showed an unique property of multiple banding patterns on SDS-PAGE at 20 mA current, with tryptic digests of all bands having similar m/z values (using MALDI-TOF) while it showed only a single band at 10 mA current. PsBGAL is effectively compartmentalized during seed maturation inside vacuoles (pH approximately 5). The enzyme is capable of hydrolyzing pea seed xyloglucan, and it may be involved in modifying the cell wall architecture during seedling growth and development. The enzyme has a protonated carboxyl group at its active site as observed by ionization constant, thermodynamics, and chemical modification studies.

A role for SENSITIVE TO FREEZING2 in protecting chloroplasts against freeze-induced damage in Arabidopsis

The sensitive to freezing2 (SFR2) gene has an important role in freezing tolerance in Arabidopsis thaliana. We show that homologous genes are present, and expressed, in a wide range of terrestrial plants, including species not able to tolerate freezing. Expression constructs derived from the cDNAs of a number of different plant species, including examples not tolerant to freezing, are able to complement the freezing sensitivity of the Arabidopsis sfr2 mutant. In Arabidopsis the SFR2 protein is localized to the chloroplast outer envelope membrane, as revealed by the analysis of transgenic plants expressing SFR2 fusions to GFP, by confocal microscopy, and by the immunological analysis of isolated chloroplasts treated with thermolysin protease. Moreover, the chloroplasts of the sfr2 mutant show clear evidence of rapid damage after a freezing episode, suggesting a role for SFR2 in the protection of the chloroplast.

Genomic and expression analysis of glycosyl hydrolase family 35 genes from rice (Oryza sativa L.)

BACKGROUND

Many plant beta-galactosidases (Bgals) have been well characterized and their deduced biological functions mainly involve degradation of structural pectins, xyloglucans or arabinogalactoproteins in plant cell walls. However, gene multiplicity in glycosyl hydrolase family 35 (GH35), to which these proteins belong, implies diverse functions. In this study, the gene multiplicity, apparent evolutionary relationships and transcript expression of rice Bgal genes were examined, in order to predict their biological functions.

RESULTS

Fifteen rice Bgal genes were identified in the plant genome, one of which encodes a protein similar to animal Bgals (OsBgal9), and the remaining 14 fall in a nearly plant-specific subfamily of Bgals. The presence of both classes of Bgals in bryophytes, as well as vascular plants, suggests both gene lineages were present early in plant evolution. All 15 proteins were predicted to contain secretory signal sequences, suggesting they have secretory pathway or external roles. RT-PCR and database analysis found two distinct lineages to be expressed nearly exclusively in reproductive tissues and to be closely related to Arabidopsis Bgals expressed most highly in flower and pollen. On the other hand, OsBgal6 is expressed primarily in young vegetative tissues, and alternative splicing in panicle prevents its production of full-length protein in this reproductive tissue. OsBgal11 also showed alternative splicing to produce different length proteins. OsBgal13 produced by recombinant expression in Escherichia coli hydrolyzed alpha-L-arabinoside in addition to beta-D-galactoside and beta-(1-->3)-, beta-(1-->4)- and beta-(1-->6)- linked galacto-oligosaccharides.

CONCLUSION

Rice GH35 contains fifteen genes with a diversity of protein sequences, predicted locations and expression and splicing patterns that suggest that OsBgals enzymes may play a variety of roles in metabolism of cell wall polysaccharides, glycoproteins and glycolipids.

The Arabidopsis At1g45130 and At3g52840 genes encode beta-galactosidases with activity toward cell wall polysaccharides

The Arabidopsis genes At1g45130 and At3g52840 encode the beta-galactosidase isozymes Gal-5 and Gal-2 that belong to Glycosyl Hydrolase Family 35 (GH 35). The two enzymes share 60% sequence identity with each other and 38-81% with other plant beta-galactosidases that are reported to be involved in cell wall modification. We studied organ-specific expression of the two isozymes. According to our western blot analysis using peptide-specific antibodies, Gal-5 and Gal-2 are most highly expressed in stem and rosette leaves. We show by dot-immunoblotting that Gal-5 and Gal-2 are associated with the cell wall in Arabidopsis. We also report expression of the recombinant enzymes in P. pastoris and describe their substrate specificities. Both enzymes hydrolyze the synthetic substrate para-nitrophenyl-beta-d-galactopyranoside and display optimal enzyme activity between pH 4.0 and 4.5, similar to the pH optimum reported for other well-characterized plant beta-galactosidases. Both Gal-5 and Gal-2 show a broad specificity for the aglycone moiety and a strict specificity for the glycone moiety in that they prefer galactose and its 6-deoxy analogue, fucose. Both enzymes cleave beta-(1,4) and beta-(1,3) linkages in galacto-oligosaccharides and hydrolyze the pectic fraction of Arabidopsis cell wall. These findings suggest that Gal-5 and Gal-2 could be involved in the modification of cell wall polysaccharides.

Purification of β-galactosidase from Erythrina indica: Involvement of tryptophan in active site

beta-Galactosidase (EC: 3.2.1.23), one of the glycosidases detected in Erythrina indica seeds, was purified to 135 fold. Amongst the four major glycosidases detected beta-galactosidase was found to be least glycosylated, and was not retained by Con-A CL Seralose affinity matrix. A homogenous preparation of the enzyme was obtained by ion-exchange chromatography, followed by gel filtration. The enzyme was found to be a dimmer with a molecular weight of 74 kDa and 78 kDa, by gel filtration and SDS-PAGE, respectively. The optimum pH and optimum temperature for enzyme activity were 4.4 and 50 degrees C, respectively. The enzyme showed a K(m) value of 2.6 mM and V(max) of 3.86 U/mg for p-nitrophenyl-beta-D-galactopyranoside as substrate and was inhibited by Zn(2+) and Hg(2+). The enzyme activity was regulated by feed back inhibition as it was found to be inhibited by beta-D-galactose. Chemical modification studies revealed involvement of tryptophan and histidine for enzyme activity. Involvement of tryptophan was also supported by fluorescence studies and one tryptophan was found to be present in the active site of beta-galactosidase. Circular dichroism studies revealed 37% alpha helix, 27% beta sheet and 38% random coil in the secondary structure of the purified enzyme.

Proteomic analysis of seed dormancy in Arabidopsis

The mechanisms controlling seed dormancy in Arabidopsis (Arabidopsis thaliana) have been characterized by proteomics using the dormant (D) accession Cvi originating from the Cape Verde Islands. Comparative studies carried out with freshly harvested dormant and after-ripened non-dormant (ND) seeds revealed a specific differential accumulation of 32 proteins. The data suggested that proteins associated with metabolic functions potentially involved in germination can accumulate during after-ripening in the dry state leading to dormancy release. Exogenous application of abscisic acid (ABA) to ND seeds strongly impeded their germination, which physiologically mimicked the behavior of D imbibed seeds. This application resulted in an alteration of the accumulation pattern of 71 proteins. There was a strong down-accumulation of a major part (90%) of these proteins, which were involved mainly in energetic and protein metabolisms. This feature suggested that exogenous ABA triggers proteolytic mechanisms in imbibed seeds. An analysis of de novo protein synthesis by two-dimensional gel electrophoresis in the presence of [(35)S]-methionine disclosed that exogenous ABA does not impede protein biosynthesis during imbibition. Furthermore, imbibed D seeds proved competent for de novo protein synthesis, demonstrating that impediment of protein translation was not the cause of the observed block of seed germination. However, the two-dimensional protein profiles were markedly different from those obtained with the ND seeds imbibed in ABA. Altogether, the data showed that the mechanisms blocking germination of the ND seeds by ABA application are different from those preventing germination of the D seeds imbibed in basal medium.

Plant glycoside hydrolases involved in cell wall polysaccharide degradation

The cell wall plays a key role in controlling the size and shape of the plant cell during plant development and in the interactions of the plant with its environment. The cell wall structure is complex and contains various components such as polysaccharides, lignin and proteins whose composition and concentration change during plant development and growth. Many studies have revealed changes in cell walls which occur during cell division, expansion, and differentiation and in response to environmental stresses; i.e. pathogens or mechanical stress. Although many proteins and enzymes are necessary for the control of cell wall organization, little information is available concerning them. An important advance was made recently concerning cell wall organization as plant enzymes that belong to the superfamily of glycoside hydrolases and transglycosidases were identified and characterized; these enzymes are involved in the degradation of cell wall polysaccharides. Glycoside hydrolases have been characterized using molecular, genetic and biochemical approaches. Many genes encoding these enzymes have been identified and functional analysis of some of them has been performed. This review summarizes our current knowledge about plant glycoside hydrolases that participate in the degradation and reorganisation of cell wall polysaccharides in plants focussing particularly on those from Arabidopsis thaliana.

Isolation of the promoter of a cotton beta-galactosidase gene (GhGal1) and its expression in transgenic tobacco plants

Beta-galactosidases (EC 3.2.1.23) constitute a widespread family of glycosyl hydrolases in plants and are thought to be involved in metabolism of cell wall polysaccharides. A cDNA of the cotton (Gossypium hirsutum) beta-galactosidase gene, designated GhGal1, has previously been identified and its transcripts are highly abundant at the elongation stage of the cotton fiber. To examine the temporal and spatial control of GhGal1 expression, a transcriptional fusion of the GhGal1 promoter region (1770 bp) with the beta-glucuronidase (GUS) reporter gene was introduced into tobacco plants by the Agrobacterium infection method. The resulting transgenic plants showed higher GUS activity of fruit in the transgenic plants than that in the negative and positive controls. Histochemical localization of GUS activity demonstrated that the expression of the GUS gene could be found in the meristem zones of roots, cotyledons, vascular tissues, fruit and trichomes in transgenic tobacco plants. Additionally, sequence analysis of the regulatory region also revealed several conserved motifs among which some were shared with previously reported fruit/seed-specific elements and the others were related with trichome expression. These results indicated the temporal and spatial expression characterization of the GhGal1 promoter in transgenic tobacco plants and provided an important insight into the roles of GhGal1 in cotton fiber development.

Purification and properties of a beta-galactosidase from carambola fruit with significant activity towards cell wall polysaccharides

beta-Galactosidase (EC. 3.2.1.23) from ripe carambola (Averrhoa carambola L. cv. B10) fruit was fractionated through a combination of ion exchange and gel filtration chromatography into four isoforms, viz. beta-galactosidase I, II, III and IV. This beta-galactosidases had apparent native molecular masses of 84, 77, 58 and 130 kDa, respectively. beta-Galactosidase I, the predominant isoform, was purified to electrophoretic homogeneity; analysis of the protein by SDS-PAGE revealed two subunits with molecular masses of 48 and 36 kDa. N-terminal amino acid sequence of the respective polypeptides shared high similarities albeit at different domains, with the deduced amino acid sequence of certain plant beta-galactosidases, thus, explaining the observed low similarity between the two subunits. beta-Galactosidase I was probably a heterodimer that have glycoprotein properties and a pI value of 7.2, with one of the potential glycosylation sites appeared to reside within the 48-kDa-polypeptide. The purified beta-galactosidase I was substantially active in hydrolyzing (1-->4)beta-linked spruce and a mixture of (1-->3)beta- and (1-->6)beta-linked gum arabic galactans. This isoform also had the capability to solubilize and depolymerize structurally intact pectins as well as to modify alkaline-soluble hemicelluloses, reflecting in part changes that occur during ripening.

A beta-galactosidase gene is expressed during mature fruit abscission of 'Valencia' orange (Citrus sinensis)

beta-galactosidases have been detected in a wide range of plants and are characterized by their ability to hydrolyse terminal non-reducing beta-D-galactosyl residues from beta-D-galactosides. These enzymes have been detected in a wide range of plant organs and tissues. In a search for differentially expressed genes during the abscission process in citrus, sequences encoding beta-galactosidase were identified. Three cDNA fragments of a beta-galactosidase gene were isolated from a cDNA subtraction library constructed from mature fruit abscission zones 48 h after the application of a mature fruit-specific abscission agent, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-pyrazole). Based on sequence information derived from these fragments, a full-length cDNA of 2847 nucleotides (GenBank accession number AY029198) encoding beta-galactosidase was isolated from mature fruit abscission zones by 5'- and 3'-RACE approaches. The beta-galactosidase cDNA encoded a protein of 737 amino acid residues with a calculated molecular weight of 82 kDa. The deduced protein was highly homologous to plant beta-galactosidases expressed in fruit ripening. Southern blot analysis demonstrated that at least two closely related beta-galactosidase genes were present in 'Valencia' orange. Temporal expression patterns in mature fruit abscission zones indicated beta-galactosidase mRNA was detected 48 h after treatment of CMN-pyrazole and ethephon in mature fruit abscission zones. beta-galactosidase transcripts were detected in leaf abscission zones only after ethephon application. The citrus beta-galactosidase was expressed in stamens and petals of fully opened flowers and young fruitlets. The results suggest that this beta-galactosidase may play a role during abscission as well as early growth and development processes in flowers and fruitlets.

Primary cell wall metabolism: tracking the careers of wall polymers in living plant cells

Numerous examples have been presented of enzyme activities, assayed in vitro, that appear relevant to the synthesis of structural polysaccharides, and to their assembly and subsequent degradation in the primary cell walls (PCWs) of higher plants. The accumulation of the corresponding mRNAs, and of the (immunologically recognized) proteins, has often also (or instead) been reported. However, the presence of these mRNAs, antigens and enzymic activities has rarely been shown to correspond to enzyme action in the living plant cell. In some cases, apparent enzymic action is observed in vivo for which no enzyme activity can be detected in in-vitro assays; the converse also occurs. Methods are reviewed by which reactions involving structural wall polysaccharides can be tracked in vivo. Special attention is given to xyloglucan endotransglucosylase (XET), one of the two enzymic activities exhibited in vitro by xyloglucan endotransglucosylase/hydrolase (XTH) proteins, because of its probable importance in the construction and restructuring of the PCW's major hemicellulose. Attention is also given to the possibility that some reactions observed in the PCW in vivo are not directly enzymic, possibly involving the action of hydroxyl radicals. It is concluded that some proposed wall enzymes, for example XTHs, do act in vivo, but that for other enzymes this is not proven. Contents I. Primary cell walls: composition, deposition and roles 642 II. Reactions that have been proposed to occur in primary cell walls 645 III. Tracking the careers of wall components in vivo: evidence for action of enzymes in the walls of living plant cells 656 IV. Evidence for the occurrence of nonenzymic polymer scission in vivo? 666 VI. Conclusion 667 References 667.

Pectin degradation in ripening and wounded fruits

Pectin depolymerization during fruit ripening has been shown to be largely due to pectinolytic enzymes, including polygalacturonases (E.C. 3.2.1.15) and pectinmethylesterases (E.C. 3.2.1.11). Studies have shown that these enzymes are not the primary determinants of softening, although participation in texture changes during the late stages of ripening seems evident. Pectin depolymerization differs significantly between various fruit types, notably avocado and tomato, even though levels of extractable PG activity in these fruits are similar. Collective evidence indicates that the activities of some cell wall enzymes are restricted in vivo, with maximum hydrolytic potential expressed only in response to tissue disruption or wounding. In contrast, other enzymes reported to participate in pectin degradation, notably beta-galactosidases/exo-galactanases, exhibit in vitro activity far below that anticipated to be required for the loss of cell wall galactosyl residues during ripening. Factors controlling in vivo hydrolysis have not been fully explored but might include apoplastic pH, cell wall inorganic ion levels, non-enzymic proteins including the noncatalytic beta-subunit and expansins, wall porosity, and steric hindrances. Recent studies of cell wall metabolism during ripening have demonstrated an orderly process involving, in the early stages, cell wall relaxation and hemicellulose degradation followed, in the later stages, by pectin depolymerization. A limited number of studies have indicated that radical oxygen species generated either enzymically or non-enzymically might participate in scission of pectins and other polysaccharides during ripening and other developmental processes. Similar mechanisms might also occur in response to wounding, an event typically followed by an oxidative burst. Cell wall degradation as influenced by physical wounding could be of particular relevance to the deterioration of lightly processed fruits.