Distinct isoforms of ADPglucose pyrophosphatase and ADPglucose pyrophosphorylase occur in the suspension-cultured cells of sycamore (Acer pseudoplatanus L.)

Protein profiling and tps23 induction in different maize lines in response to methyl jasmonate treatment and Diabrotica virgifera infestation

Plant responses to herbivore insects involve direct and indirect defense with the production of signal molecules including jasmonic acid (JA) and its derivatives (e.g. methyl jasmonate, MeJA). In maize (Zea mays), root feeding by Diabrotica virgifera larvae activates an indirect defense mechanism, through enthomopathogenic nematodes that are recruited after Terpene Synthase 23 (tps23) upregulation and (E)-β-caryophyllene root emission. In order to gain insight into the correlation between JA signaling and response to Diabrotica attack, we analyzed tps23 expression and protein profiles in maize roots in response to MeJA treatment and insect infestation. Similar to herbivore feeding, MeJA treatment was found to increase tps23 transcript accumulation, with consistent variations for both treatments in maize lines differing in (E)-β-caryophyllene production. Analysis of root protein profiles showed specific alterations leading to the identification of three proteins that were induced by MeJA treatment. We focused on a peroxidase-like protein (Px-like) showing that the corresponding transcripts accumulated in all tested lines. Results show that exogenous application of MeJA upregulates tps23 expression and specifically alters protein patterns in maize roots. Parallel effects on tps23 transcript accumulation were observed upon hormone exposure and insect infestation in different maize lines. In contrast, Px-like transcript profiling showed differences between treatments. These results support the possible involvement of MeJA in mediating the upregulation of tps23 in response to Diabrotica attack.

Bioseparation of Four Proteins from Euphorbia characias Latex: Amine Oxidase, Peroxidase, Nucleotide Pyrophosphatase/Phosphodiesterase, and Purple Acid Phosphatase

This paper deals with the purification of four proteins from Euphorbia characias latex, a copper amine oxidase, a nucleotide pyrophosphatase/phosphodiesterase, a peroxidase, and a purple acid phosphatase. These proteins, very different in molecular weight, in primary structure, and in the catalyzed reaction, are purified using identical preliminary steps of purification and by chromatographic methods. In particular, the DEAE-cellulose chromatography is used as a useful purification step for all the four enzymes. The purification methods here reported allow to obtain a high purification of all the four proteins with a good yield. This paper will give some thorough suggestions for researchers busy in separation of macromolecules from different sources.

Rice plastidial N-glycosylated nucleotide pyrophosphatase/phosphodiesterase is transported from the ER-golgi to the chloroplast through the secretory pathway

A nucleotide pyrophosphatase/phosphodiesterase (NPP) activity that catalyzes the hydrolytic breakdown of ADP-glucose (ADPG) has been shown to occur in the plastidial compartment of both mono- and dicotyledonous plants. To learn more about this enzyme, we purified two NPPs from rice (Oryza sativa) and barley (Hordeum vulgare) seedlings. Both enzymes are glycosylated, since they bind to concanavalin A, stain with periodic acid-Schiff reagent, and are digested by Endo-H. A complete rice NPP cDNA, designated as NPP1, was isolated, characterized, and overexpressed in transgenic plants displaying high ADPG hydrolytic activity. Databank searches revealed that NPP1 belongs to a functionally divergent group of plant nucleotide hydrolases. NPP1 contains numerous N-glycosylation sites and a cleavable hydrophobic signal sequence that does not match with the N-terminal part of the mature protein. Both immunocytochemical analyses and confocal fluorescence microscopy of rice cells expressing NPP1 fused with green fluorescent protein (GFP) revealed that NPP1-GFP occurs in the plastidial compartment. Brefeldin A treatment of NPP1-GFP-expressing cells prevented NPP1-GFP accumulation in the chloroplasts. Endo-H digestibility studies revealed that both NPP1 and NPP1-GFP in the chloroplast are glycosylated. Collectively, these data demonstrate the trafficking of glycosylated proteins from the endoplasmic reticulum-Golgi system to the chloroplast in higher plants.

Cloning, expression and characterization of a Nudix hydrolase that catalyzes the hydrolytic breakdown of ADP-glucose linked to starch biosynthesis in Arabidopsis thaliana

'Nudix' hydrolases are widely distributed nucleotide pyrophosphatases that possess a conserved GX5EX7REUXEEXGU motif where U is usually isoleucine, leucine or valine. Among them, Escherichia coli ADP-sugar pyrophosphatase (ASPP) has been shown to catalyze the hydrolytic breakdown of ADP-glucose linked to bacterial glycogen biosynthesis. Comparisons of the 31 different Nudix-encoding sequences of the Arabidopsis genome with those coding for known bacterial and mammalian ASPPs identified one sequence possessing important divergences in the Nudix motif that, once expressed in E. coli, produced a protein with ASPP activity. This protein, designated as AtASPP, shares strong homology with hypothetical rice and potato proteins, indicating that ASPPs are widely distributed in both mono- and dicotyledonous plants. As a first step to test the possible involvement of plant ASPPs in regulating the intracellular levels of ADP-glucose linked to starch biosynthesis, we produced and characterized AtASPP-overexpressing Arabidopsis plants. Source leaves from these plants exhibited a large reduction in the levels of both ADP-glucose and starch, indicating that plant ASPPs catalyze the hydrolytic breakdown of a sizable pool of ADP-glucose linked to starch biosynthesis. No pleiotropic changes in maximum catalytic activities of enzymes closely linked to starch metabolism could be detected in AtASPP-overexpressing leaves. The overall information provides the first evidence for the existence of plant Nudix hydrolases that have access to an intracellular pool of ADP-glucose linked to starch biosynthesis.

Cloning and expression analysis of Zmglp1, a new germin-like protein gene in maize

The cDNA and genomic DNA of a green tissue-specific gene were cloned from maize (Zea mays L.) using cDNA-amplified fragment length polymorphism (cDNA-AFLP) and library screening. The deduced protein was highly similar to Hordeum vulgare germin-like protein 1 (HvGLP1), and the maize gene was therefore designated Zmglp1. Northern blot specifically detected the mRNA of Zmglp1 in young whorl leaves at the early-whorl stage. However, at the late-whorl, tassel, and silk stages, Zmglp1 transcripts were highly abundant in young whorl leaves; less abundant in mature leaves, young tassels, and cobs; and not detectable in roots, immature kernels, and stalks. RNA in situ hybridization revealed that Zmglp1 expressed only in mesophyllous, phloem, and guard cells in the young whorl leaves. Deletion analysis of the promoter in transgenic Arabidopsis resulted in the identification of several regions containing important regulatory cis-elements controlling the expression levels and circadian rhythm-oscillated patterns of Zmglp1.

Most of ADP x glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves

Sucrose and starch are end products of two segregated gluconeogenic pathways, and their production takes place in the cytosol and chloroplast of green leaves, respectively. According to this view, the plastidial ADP.glucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule ADPG. However, a growing body of evidences indicates that starch formation involves the import of cytosolic ADPG to the chloroplast. This evidence is consistent with the idea that synthesis of the ADPG linked to starch biosynthesis takes place in the cytosol by means of sucrose synthase, whereas AGP channels the glucose units derived from the starch breakdown. To test this hypothesis, we first investigated the subcellular localization of ADPG. Toward this end, we constructed transgenic potato plants that expressed the ADPG-cleaving adenosine diphosphate sugar pyrophosphatase (ASPP) from Escherichia coli either in the chloroplast or in the cytosol. Source leaves from plants expressing ASPP in the chloroplast exhibited reduced starch and normal ADPG content as compared with control plants. Most importantly however, leaves from plants expressing ASPP in the cytosol showed a large reduction of the levels of both ADPG and starch, whereas hexose phosphates increased as compared with control plants. No pleiotropic changes in photosynthetic parameters and maximum catalytic activities of enzymes closely linked to starch and sucrose metabolism could be detected in the leaves expressing ASPP in the cytosol. The overall results show that, essentially similar to cereal endosperms, most of the ADPG linked to starch biosynthesis in source leaves occurs in the cytosol.

Targeted expression of human serum albumin to potato tubers

Complementary DNA expression of mature human serum albumin was engineered into potato plants under the transcriptional control of patatin B33 promoter and potato proteinase inhibitor II terminator. Protein secretion was achieved by using the signal sequence from potato proteinase inhibitor II. Recombinant albumin accumulated up to 0.2% of total soluble tuber protein in single transformant lines, regardless of the potato cultivar used. Electrophoretic mobility and N-terminal amino acid sequence analysis of partially purified recombinant albumin confirmed proper processing of an immune responsive recombinant albumin, and revealed that the proteinase inhibitor II signal sequence was correctly removed. No further optimisation of these yields was obtained by HSA expression in patatin antisense plants (line Pas58). Subcellular localisation showed that recombinant protein was successfully targeted to the apoplast. Potato tubers may be used, by applying this technology, to produce other heterologous proteins of interest in the biopharmaceutical industry.

Reappraisal of the currently prevailing model of starch biosynthesis in photosynthetic tissues: a proposal involving the cytosolic production of ADP-glucose by sucrose synthase and occurrence of cyclic turnover of starch in the chloroplast

A vast amount of information has accumulated which supports the view that sucrose and starch are end-products of two segregated, yet highly interconnected, gluconeogenic pathways taking place in the cytosol and chloroplast, respectively. However, several lines of experimental evidences indicate that, essentially identical to the case of heterotrophic tissues, starch formation in the photosynthetic tissues may involve the direct import to the chloroplast of cytosolic hexose (C6) units derived from the sucrose breakdown. This evidence is consistent with the idea that synthesis of a sizable pool of ADP-glucose takes place in the cytosol by means of sucrose synthase whereas, basically in agreement with recent investigations dealing with glycogen biosynthesis in bacteria and animals, chloroplastic phosphoglucomutase and ADP-glucose pyrophosphorylase are most likely playing a role in channelling of glucose units derived from the starch breakdown in the chloroplast, thus making up a regulatory starch turnover cycle. According to this new view, we propose that starch production in the chloroplast is the result of a flexible and dynamic mechanism wherein both catabolic and anabolic reactions take place simultaneously in a highly interactive manner. Starch is seen as an intermediate component of a cyclic gluconeogenic pathway which, in turn, is connected with other metabolic pathways. The possible importance of metabolic turnover as a way to control starch production is exemplified with the recently discovered ADP-glucose pyrophosphatase, an enzyme likely having a dual role in controlling levels of ADP-glucose linked to starch biosynthesis and diverting carbon flow towards other metabolic pathways.

Two isoforms of a nucleotide-sugar pyrophosphatase/phosphodiesterase from barley leaves (Hordeum vulgare L.) are distinct oligomers of HvGLP1, a germin-like protein

Two isoforms of ADPglucose pyrophosphatase/phosphodiesterase (AGPPase) have been characterized using barley leaves (Hordeum vulgare L.). Whilst one of the isoforms, designated as soluble AGPPase1 (SAGPPase1), is soluble in low ionic strength buffers, the other, SAGPPase2, is extractable using cell wall hydrolytic enzymes or high salt concentration solutions, thus indicating that it is adventitiously bound to the cell wall. Both AGPPase isoforms are highly resistant to SDS, this characteristic being utilized to purify them to homogeneity after zymographic detection of AGPPase activity in SDS-containing gels. N-terminal and internal amino acid sequencing analyses revealed that both SAGPPase1 and SAGPPase2 are distinct oligomers of the previously designated HvGLP1, which is a member of the ubiquitously distributed group of proteins of unknown function designated as germin-like proteins (GLPs).