Plastidial <i>α</i>-Glucan Phosphorylase Is Not Required for Starch Degradation in Arabidopsis Leaves But Has a Role in the Tolerance of Abiotic Stress

Zeeman, Samuel C.; Thorneycroft, David; Schupp, Nicole; Chapple, Andrew G.; Weck, Melanie N.; Dunstan, Hannah; Haldimann, Pierre; Bechtold, Nicole; Smith, Alison M.; Smith, Steven M.

doi:10.1104/pp.103.032631

Cited by 222 publications

(155 citation statements)

References 47 publications

(56 reference statements)

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“…None of the three candidate proteins participating in the metabolism of starch was previously recognized as a Trx target. One, ␣-1,4-glucan phosphorylase, releases glucose 1-phosphate from the starch chain, possibly as part of a stress response (29,30). Trx seems ideal to participate in such a response by way of the oxidative regulatory mechanism described for certain chloroplast enzymes, e.g., transketolase (5).…”

Section: Identification Of Members Of the Ferredoxin͞trx System And Smentioning

confidence: 99%

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

Balmer

Vensel

Cai

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

160

137

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A growing number of processes throughout biology are regulated by redox via thiol-disulfide exchange. This mechanism is particularly widespread in plants, where almost 200 proteins have been linked to thioredoxin (Trx), a widely distributed small regulatory disulfide protein. The current study extends regulation by Trx to amyloplasts, organelles prevalent in heterotrophic plant tissues that, among other biosynthetic activities, catalyze the synthesis and storage of copious amounts of starch. Using proteomics and immunological methods, we identified the components of the ferredoxin͞Trx system (ferredoxin, ferredoxin-Trx reductase, and Trx), originally described for chloroplasts, in amyloplasts isolated from wheat starchy endosperm. Ferredoxin is reduced not by light, as in chloroplasts, but by metabolically generated NADPH via ferredoxin-NADP reductase. However, once reduced, ferredoxin appears to act as established for chloroplasts, i.e., via ferredoxinTrx reductase and a Trx (m-type). A proteomics approach in combination with affinity chromatography and a fluorescent thiol probe led to the identification of 42 potential Trx target proteins, 13 not previously recognized, including a major membrane transporter (Brittle-1 or ADP-glucose transporter). The proteins function in a range of processes in addition to starch metabolism: biosynthesis of lipids, amino acids, and nucleotides; protein folding; and several miscellaneous reactions. The results suggest a mechanism whereby light is initially recognized as a thiol signal in chloroplasts, then as a sugar during transit to the sink, where it is converted again to a thiol signal. In this way, amyloplast reactions in the grain can be coordinated with photosynthesis taking place in leaves.redox regulation ͉ target proteins ͉ ferredoxin-thioredoxin reductase O ur understanding of the function of the regulatory disulfide protein thioredoxin (Trx) has increased dramatically in the past few years, with the advent of new methodologies. Recent approaches make it possible to identify proteins linked to Trx by combining proteomics with affinity chromatography (1) or thiol probes (2-4). These capabilities have defined an extended role of Trx in chloroplasts (1, 5) and helped elucidate its function in other plant systems: mitochondria (6), seeds (2,3,7,8), and seedlings (4, 9). Currently almost 200 proteins appear to be linked to Trx in plants (10). One major organelle that has been neglected, however, is the amyloplast, a plastid of heterotrophic tissues that performs a wide range of biosynthetic reactions, including the synthesis and storage of abundant quantities of starch.To help fill this gap, we have applied proteomic and immunological approaches to investigate the occurrence and function of Trx in amyloplasts. We now report evidence that amyloplasts isolated from wheat starchy endosperm resemble chloroplasts in containing a complete ferredoxin͞Trx system composed of ferredoxin, ferredoxin-Trx reductase (FTR), and Trx (m-type). Application of affinity chromatography and fl...

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Section: Identification Of Members Of the Ferredoxin͞trx System And Smentioning

confidence: 99%

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

Balmer

Vensel

Cai

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

160

137

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“…For the dpe2-1 line, see Lu and Sharkey (2004). The PHS1-deficient line in background Ws has been described by Zeeman et al (2004). The PHS1-deficient line in background Col-0 was generated using GK-257A06.03.…”

Section: Plant Materialsmentioning

confidence: 99%

Double Knockout Mutants of Arabidopsis Grown under Normal Conditions Reveal that the Plastidial Phosphorylase Isozyme Participates in Transitory Starch Metabolism

et al. 2013

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In leaves of two starch-related single-knockout lines lacking either the cytosolic transglucosidase (also designated as disproportionating enzyme 2, DPE2) or the maltose transporter (MEX1), the activity of the plastidial phosphorylase isozyme (PHS1) is increased. In both mutants, metabolism of starch-derived maltose is impaired but inhibition is effective at different subcellular sites. Two constitutive double knockout mutants were generated (designated as dpe2-1 × phs1a and mex1 × phs1b) both lacking functional PHS1. They reveal that in normally grown plants, the plastidial phosphorylase isozyme participates in transitory starch degradation and that the central carbon metabolism is closely integrated into the entire cell biology. All plants were grown either under continuous illumination or in a light-dark regime. Both double mutants were compromised in growth and, compared with the single knockout plants, possess less average leaf starch when grown in a light-dark regime. Starch and chlorophyll contents decline with leaf age. As revealed by transmission electron microscopy, mesophyll cells degrade chloroplasts, but degradation is not observed in plants grown under continuous illumination. The two double mutants possess similar but not identical phenotypes. When grown in a light-dark regime, mesophyll chloroplasts of dpe2-1 × phs1a contain a single starch granule but under continuous illumination more granules per chloroplast are formed. The other double mutant synthesizes more granules under either growth condition. In continuous light, growth of both double mutants is similar to that of the parental single knockout lines. Metabolite profiles and oligoglucan patterns differ largely in the two double mutants.

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“…It is synthesized mainly during photosynthesis in the light period buffering CO 2 fixation or in storage organs like tubers, bulbs, or seeds (Dennis and Blakeley, 2000). In recent years, numerous studies have been performed to increase knowledge of starch metabolism, including in the model plant Arabidopsis (Arabidopsis thaliana; Zeeman et al, 2002Zeeman et al, , 2004Siedlecka et al, 2003;Smith et al, 2004;Delvallé et al, 2005;Lloyd et al, 2005;Dumez et al, 2006). In most of these studies, plant leaf material of the wild type and mutant lines was used to investigate starch metabolism under different light regimes or altered sugar concentrations.…”

mentioning

confidence: 99%

Starch Serves as Carbohydrate Storage in Nematode-Induced Syncytia

et al. 2007

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The plant parasitic nematode Heterodera schachtii induces specific syncytial feeding sites in the roots of Arabidopsis thaliana from where it withdraws all required nutrients. Therefore, syncytia have to be well supplied with assimilates and generate strong sinks in the host plant's transport system. Import mechanisms and consequent accumulation of sucrose in syncytia were described recently. In this work, we studied the starch metabolism of syncytia. Using high-performance liquid chromatography and microscopic analyses, we demonstrated that syncytia store carbohydrates by starch accumulation. Further, we monitored the expression of genes involved in the starch metabolic pathway by gene chip analysis and quantitative reverse transcription-PCR. Finally, we provide functional proof of the importance of starch synthesis for nematode development using T-DNA insertion lines. We conclude that syncytia accumulate starch as a carbohydrate buffer to compensate for changing solute uptake by the nematode and as long-term storage during juvenile development.

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Plastidial α-Glucan Phosphorylase Is Not Required for Starch Degradation in Arabidopsis Leaves But Has a Role in the Tolerance of Abiotic Stress

Cited by 222 publications

References 47 publications

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

Double Knockout Mutants of Arabidopsis Grown under Normal Conditions Reveal that the Plastidial Phosphorylase Isozyme Participates in Transitory Starch Metabolism

Starch Serves as Carbohydrate Storage in Nematode-Induced Syncytia

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