S<scp>UGAR</scp>-I<scp>NDUCED</scp> S<scp>IGNAL</scp> T<scp>RANSDUCTION IN</scp> P<scp>LANTS</scp>

Smeekens, Sjef

doi:10.1146/annurev.arplant.51.1.49

Cited by 677 publications

(112 citation statements)

References 189 publications

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“…The greater accumulation of starch in leaves transferred from LL to HL relative to that found in HL-acclimated leaves suggests a more limiting carbon export capacity in pumpkin (and perhaps V. phoeniceum), whereas excess starch accumulation was not observed in the apoplastic loaders pea and spinach. Down-regulation of photosynthesis is a common response when the synthesis of sugars far exceeds their export and utilization (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Such repression of photosynthesis would be expected to impact photosynthetic capacity, as was consistently observed for both symplastic loaders compared with the apoplastic loaders in the present study.…”

Section: Photosynthetic Acclimation In the Symplastic Loaders Pumpkinsupporting

confidence: 71%

Anatomical and photosynthetic acclimation to the light environment in species with differing mechanisms of phloem loading

Amiard

Mueh

Ebbert

et al. 2005

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

139

171

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Plants load sugars from photosynthesizing leaves into the phloem of exporting veins either ''apoplastically'' (by using H ؉ ͞sucrose symporters) or ''symplastically'' (through plasmodesmata). The ability to regulate photosynthesis in response to the light environment was compared among apoplastic loaders (pea and spinach) and symplastic loaders (pumpkin and Verbascum phoeniceum). Plants were grown under low light (LL) or high light (HL) or transferred from LL to HL. Upon transfer, pea and spinach upregulated photosynthesis to the level found in HL-acclimated plants, whereas up-regulation in pumpkin and V. phoeniceum was limited. The vein density of pea and spinach was the same in HL and LL. Although spinach did not exhibit anatomical or ultrastructural acclimation to the light environment, in pea, wall invaginations in minor vein companion (transfer) cells were more extensive in HL. Furthermore, upon transfer from LL to HL, these invaginations increased in mature pea leaves. Foliar starch levels in mature leaves of plants transferred from LL to HL were not greater than in HL-acclimated leaves of either apoplastically loading species. In the symplastic loaders, plasmodesmatal frequency per loading cell did not vary with treatment, but vein density and thus total plasmodesmatal frequency were higher in HL. Upon transfer of symplastic loaders, however, vein density remained low, and starch levels were higher than in HL; the incomplete acclimation of photosynthesis upon transfer is thus consistent with a carbon export capacity physically limited by an inability to increase vein and plasmodesmatal density in a mature leaf. apoplastic loading ͉ leaf vein density ͉ photosynthesis ͉ symplastic loading ͉ transfer cells P lants adjust their capacity to carry out photosynthesis in response to the demand for photosynthetic products. This balance between source (mature, photosynthesizing leaves) and sinks (growing, metabolizing, and storing tissues) is continuously adjusted in response to environmental and developmental cues (1, 2). When sink activity is high during rapid growth, photosynthesis rates are high, whereas photosynthesis is typically down-regulated when sink activity is lowered [for example, after fruit removal (3) or in response to decreased soil nitrogen availability (4)]. Similarly, photosynthesis is down-regulated in response to external sugar feeding of leaves or plants (5-7), inhibition of sucrose export resulting from overexpression of an apoplastic invertase (8-10), elevated CO 2 levels (11, 12), and inhibition of export by cold-girdling petioles (10, 13). Despite the preponderance of evidence from such manipulative experiments in support of source-sink feedback regulation of photosynthetic capacity, there has been no examination of the potential role of variation in foliar carbon export features that might influence acclimation of photosynthesis to varying environmental conditions.One of the most profound differences among plant species in terms of carbon export from source tissues is the mode of phloem ...

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Section: Photosynthetic Acclimation In the Symplastic Loaders Pumpkinsupporting

confidence: 71%

Anatomical and photosynthetic acclimation to the light environment in species with differing mechanisms of phloem loading

Amiard

Mueh

Ebbert

et al. 2005

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

139

171

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“…More recent studies in potato tubers revealed that sucrose and glucose lead to redox activation of AGPase via two different signaling pathways involving SNF1-related protein kinase (SnRK1) and hexokinase, respectively (16). Hexokinase and SnRK1 are both implicated in a regulatory network that controls the expression and phosphorylation of cytosolic enzymes in response to sugars (17). How they are linked to reductive activation of AGPase and starch synthesis in the plastid remains unresolved.…”

mentioning

confidence: 99%

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

Kolbe

Tiessen

Schluepmann³

et al. 2005

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

351

320

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Trehalose is the most widespread disaccharide in nature, occurring in bacteria, fungi, insects, and plants. Its precursor, trehalose 6-phosphate (T6P), is also indispensable for the regulation of sugar utilization and growth, but the sites of action are largely unresolved. Here we use genetic and biochemical approaches to investigate whether T6P acts to regulate starch synthesis in plastids of higher plants. Feeding of trehalose to Arabidopsis leaves led to stimulation of starch synthesis within 30 min, accompanied by activation of ADP-glucose pyrophosphorylase (AGPase) via posttranslational redox modification. The response resembled sucrose but not glucose feeding and depended on the expression of SNF1-related kinase. We also analyzed transgenic Arabidopsis plants with T6P levels increased by expression of T6P synthase or decreased by expression of T6P phosphatase (TPP) in the cytosol. Compared with wild type, leaves of T6P synthase-expressing plants had increased redox activation of AGPase and increased starch, whereas TPP-expressing plants showed the opposite. Moreover, TPP expression prevented the increase in AGPase activation in response to sucrose or trehalose feeding. Incubation of intact isolated chloroplasts with 100 M T6P significantly and specifically increased reductive activation of AGPase within 15 min. Results provide evidence that T6P is synthesized in the cytosol and acts on plastidial metabolism by promoting thioredoxin-mediated redox transfer to AGPase in response to cytosolic sugar levels, thereby allowing starch synthesis to be regulated independently of light. The discovery informs about the evolution of plant metabolism and how chloroplasts of prokaryotic origin use an intermediate of the ancient trehalose pathway to report the metabolic status of the cytosol.SNF1 kinase ͉ sugar signaling ͉ thioredoxin S tarch is the major carbon store in plants consisting of an insoluble polymer of ␣-1,4-and ␣-1,6-linked glucose units (1). In the chloroplast of leaves, starch is synthesized during the day as a transient store, which is degraded during the night to support nonphotosynthetic leaf metabolism and sucrose export. In heterotrophic storage organs such as potato tubers, most of the incoming sucrose is converted to starch as a long-term carbon store for reproductive growth. In addition to its central role in carbon metabolism of plants, starch is also of great economical importance and is used for food and feed purposes and many industrial applications (2).ADP-glucose pyrophosphorylase (AGPase) catalyzes the first committed step of starch synthesis in the plastid, converting glucose 1-phosphate and ATP to ADP-glucose and PP i . ADP-glucose is subsequently used by starch synthases and branching enzymes to elongate the glucan chains of the starch granule. AGPase is a heterotetramer that contains two large (AGPS, 51 kDa) and two slightly smaller subunits (AGPB, 50 kDa) (3, 4). Work with Arabidopsis mutants (5) and potato tubers (6) showed that the enzyme catalyzes a near rate-limiting step in the pat...

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“…Transformants were screened for resistance to the herbicide Basta TM . For analysis of GUS activity, tissue samples of T2 transformants were treated with GUS staining buffer (100 mM Na 2 HPO 4 /NaH 2 PO 4 ), pH 7.0, 10 mM Na 2 EDTA, 0.5 mM K 3 [Fe(CN)6], 0.5 mM K 4 [Fe(CN) 6 ], and 0.08% X-GlcA (Duchefa, Haarlem, The Netherlands) for 20 h at 37°C. Green tissues were bleached with ethanol before examination.…”

Section: Generation Of Promoter::gus Plantsmentioning

confidence: 99%

“…Acid invertases are responsible for sucrose unloading from the conducting tissues and for the adjustment of the hexose/sucrose ratio, which affects plant development including programmed cell death [3]. Thus, the hexose/sucrose ratio acts as an important metabolic signal, which dramatically affects gene expression profiles [4][5][6][7][8]. Consequently, the expression patterns of CWI and VI have to be tightly controlled, both temporally and spatially.…”

Section: Introductionmentioning

confidence: 99%

In Arabidopsis thaliana, the invertase inhibitors AtC/VIF1 and 2 exhibit distinct target enzyme specificities and expression profiles

2004

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Plant cell wall (CWI) and vacuolar invertases (VI) play important roles in carbohydrate metabolism, stress responses and sugar signaling. Addressing the regulation of invertase activities by inhibitor proteins (C/VIF, cell wall/ vacuolar inhibitor of fructosidase), we have identified two C/ VIFs from Arabidopsis thaliana. AtC/VIF1 showed specific inhibition of VI activity, whereas AtC/VIF2 inhibited both, CWI and VI. Expression analysis revealed that expression of AtC/ VIF1 was restricted to specific organs, AtC/VIF2, however, was weakly expressed throughout plant development. Promoter::GUS transformants confirmed pronounced differences of tissue/cell type-specific expression between both isoforms. Growth of an AtC/VIF1 T-DNA KO mutant was unaffected, but VI activity and hexose content were slightly increased.

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SUGAR-INDUCED SIGNAL TRANSDUCTION IN PLANTS

Cited by 677 publications

References 189 publications

Anatomical and photosynthetic acclimation to the light environment in species with differing mechanisms of phloem loading

Anatomical and photosynthetic acclimation to the light environment in species with differing mechanisms of phloem loading

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

In Arabidopsis thaliana, the invertase inhibitors AtC/VIF1 and 2 exhibit distinct target enzyme specificities and expression profiles

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