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Title: A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley

Abstract

Sequential carbohydrate synthesis is important for plant survival because it guarantees energy supplies for growth and development during plant ontogeny and reproduction. Starch and fructan are two important carbohydrates in many flowering plants and in human diets. Understanding this coordinated starch and fructan synthesis and unraveling how plants allocate photosynthates and prioritize different carbohydrate synthesis for survival could lead to improvements to cereals in agriculture for the purposes of greater food security and production quality. Here, we report a system from a single gene in barley employing two alternative promoters, one intronic/exonic, to generate two sequence-overlapping but functionally opposing transcription factors, in sensing sucrose, potentially via sucrose/glucose/fructose/trehalose 6-phosphate signaling. The system employs an autoregulatory mechanism in perceiving a sucrose-controlled trans activity on one promoter and orchestrating the coordinated starch and fructan synthesis by competitive transcription factor binding on the other promoter. As a case in point for the physiological roles of the system, we have demonstrated that this multitasking system can be exploited in breeding barley with tailored amounts of fructan to produce healthy food ingredients. The identification of an intron/exon-spanning promoter in a hosting gene, resulting in proteins with distinct functions, adds to the complexity of plant genomes.

Authors:
 [1];  [2];  [3];  [1];  [4];  [4];  [3];  [5];  [3];  [6];  [7];  [6];  [8];  [9];  [6];  [3]
  1. Hunan Agricultural University (China). Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization; Swedish University of Agricultural Sciences, Uppsala (Sweden). Department of Plant Biology, Uppsala BioCenter, Linnean Centre for Plant Biology
  2. Hunan Agricultural University (China). Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization and Key Laboratory of Education, Department of Hunan Province on Plant Genetics and Molecular Biology, College of Bioscience and Biotechnology; Swedish University of Agricultural Sciences, Uppsala (Sweden). Department of Plant Biology, Uppsala BioCenter, Linnean Centre for Plant Biology
  3. Swedish University of Agricultural Sciences, Uppsala (Sweden). Department of Plant Biology, Uppsala BioCenter, Linnean Centre for Plant Biology
  4. Swedish University of Agricultural Sciences, Uppsala (Sweden). Department of Chemistry and Biotechnology, Uppsala BioCenter
  5. The Swedish NMR Centre at University of Gothenburg (Sweden)
  6. Swedish University of Agricultural Sciences, Uppsala (Sweden). Department of Molecular Sciences, Uppsala BioCenter
  7. Hunan Agricultural University (China). Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization and Key Laboratory of Education, Department of Hunan Province on Plant Genetics and Molecular Biology, College of Bioscience and Biotechnology
  8. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
  9. Hunan Agricultural University (China). Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1413506
Report Number(s):
PNNL-SA-130518
Journal ID: ISSN 1674-2052; PII: S1674205217303325
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Molecular Plant
Additional Journal Information:
Journal Volume: 10; Journal Issue: 12; Journal ID: ISSN 1674-2052
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Jin, Yunkai, Fei, Mingliang, Rosenquist, Sara, Jin, Lu, Gohil, Suresh, Sandström, Corine, Olsson, Helena, Persson, Cecilia, Höglund, Anna-Stina, Fransson, Gunnel, Ruan, Ying, Åman, Per, Jansson, Christer, Liu, Chunlin, Andersson, Roger, and Sun, Chuanxin. A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley. United States: N. p., 2017. Web. doi:10.1016/J.MOLP.2017.10.013.
Jin, Yunkai, Fei, Mingliang, Rosenquist, Sara, Jin, Lu, Gohil, Suresh, Sandström, Corine, Olsson, Helena, Persson, Cecilia, Höglund, Anna-Stina, Fransson, Gunnel, Ruan, Ying, Åman, Per, Jansson, Christer, Liu, Chunlin, Andersson, Roger, & Sun, Chuanxin. A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley. United States. doi:10.1016/J.MOLP.2017.10.013.
Jin, Yunkai, Fei, Mingliang, Rosenquist, Sara, Jin, Lu, Gohil, Suresh, Sandström, Corine, Olsson, Helena, Persson, Cecilia, Höglund, Anna-Stina, Fransson, Gunnel, Ruan, Ying, Åman, Per, Jansson, Christer, Liu, Chunlin, Andersson, Roger, and Sun, Chuanxin. 2017. "A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley". United States. doi:10.1016/J.MOLP.2017.10.013. https://www.osti.gov/servlets/purl/1413506.
@article{osti_1413506,
title = {A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley},
author = {Jin, Yunkai and Fei, Mingliang and Rosenquist, Sara and Jin, Lu and Gohil, Suresh and Sandström, Corine and Olsson, Helena and Persson, Cecilia and Höglund, Anna-Stina and Fransson, Gunnel and Ruan, Ying and Åman, Per and Jansson, Christer and Liu, Chunlin and Andersson, Roger and Sun, Chuanxin},
abstractNote = {Sequential carbohydrate synthesis is important for plant survival because it guarantees energy supplies for growth and development during plant ontogeny and reproduction. Starch and fructan are two important carbohydrates in many flowering plants and in human diets. Understanding this coordinated starch and fructan synthesis and unraveling how plants allocate photosynthates and prioritize different carbohydrate synthesis for survival could lead to improvements to cereals in agriculture for the purposes of greater food security and production quality. Here, we report a system from a single gene in barley employing two alternative promoters, one intronic/exonic, to generate two sequence-overlapping but functionally opposing transcription factors, in sensing sucrose, potentially via sucrose/glucose/fructose/trehalose 6-phosphate signaling. The system employs an autoregulatory mechanism in perceiving a sucrose-controlled trans activity on one promoter and orchestrating the coordinated starch and fructan synthesis by competitive transcription factor binding on the other promoter. As a case in point for the physiological roles of the system, we have demonstrated that this multitasking system can be exploited in breeding barley with tailored amounts of fructan to produce healthy food ingredients. The identification of an intron/exon-spanning promoter in a hosting gene, resulting in proteins with distinct functions, adds to the complexity of plant genomes.},
doi = {10.1016/J.MOLP.2017.10.013},
journal = {Molecular Plant},
number = 12,
volume = 10,
place = {United States},
year = 2017,
month =
}

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  • Previous work showed that the segl mutant of barley (Hordeum vulgare o Betzes) did not differ from normal Betzes in plant growth, photosynthesis, or fertility, but it produced only shrunken seeds regardless of pollen source. To determine whether defects in sucrose uptake or starch synthesis resulted in the shrunken condition, developing grains of Betzes and segl were cultured in (/sup 14/C)sucrose solutions after slicing transversely to expose the endosperm cavity and free space. In both young grains (before genotypes differed in dry weight) and older grains (17 days after anthesis, when segl grains were smaller than Betzes), sucrose uptake andmore » starch synthesis were similar in both genotypes on a dry weight basis. To determine if sucrose was hydrolyzed during uptake, spikes of Betzes and segl were allowed to take up (fructose-U-/sup 14/C)sucrose 14 days after anthesis and the radioactivity of endosperm sugars was examined during 3 hours of incubation. Whereas less total radioactivity entered the endosperm and the endosperm cavity (free space) of segl, in both genotypes over 96% of the label of endosperm sugars was in sucrose, and there was no apparent initial or progressive randomization of label among hexose moieties of sucrose as compared to the free space sampled after 1 hour of incubation. The authors conclude that segl endosperms are capable of normal sucrose uptake and starch synthesis and that hydrolysis of sucrose is not required for uptake in either genotype. Evidence suggests abnormal development of grain tissue of maternal origin during growth of segl grains.« less
  • Mild water stress, on the order of {minus}1.0 megapascals xylem water potential, can reduce the rate of photosynthesis and eliminate the inhibition of photosynthesis caused by O{sub 2} in water-stress-sensitive plants such as Phaseolus vulgaris. To investigate the lack of O{sub 2} inhibition of photosynthesis, we measured stromal and cytosolic fructose-1,6-bisphosphatase, sucrose phosphate synthase, and partitioning of newly fixed carbon between starch and sucrose before, during, and after mild water stress. The extractable activity of the fructose bisphosphatases was unaffected by mild water stress. The extractable activity of SPS was inhibited by more than 60% in plants stressed to watermore » potentials of {minus}0.9 megapascals. Water stress caused a decline in the starch/sucrose partitioning ratio indicating that starch synthesis was inhibited more than sucrose synthesis. We conclude that the reduced rate of photosynthesis during water stress is caused by stomatal closure, and that the restriction of CO{sub 2} supply caused by stomatal closure leads to a reduction in the capacity for both starch and sucrose synthesis. This causes the reduced O{sub 2} inhibition and abrupt CO{sub 2} saturation of photosynthesis.« less
  • Phaseolus vulgaris L. leaves were subjected to various light, CO/sub 2/, and O/sub 2/ levels and abscisic acid, then given a 10 minute pulse of /sup 14/CO/sub 2/ followed by a 5 minute chase with unlabeled CO/sub 2/. After the chase period, very little label remained in the ionic fractions except at low CO/sub 2/ partial pressure. Most label was found in the neutral, alcohol soluble fraction or in the insoluble fraction digestable by amyloglucosidase. Sucrose formation was linearly related to assimilation rate. Starch formation increased linearly with assimilation rate, but did not occur if the assimilation rate was belowmore » 4 micromoles per square meter per second. Neither abscisic acid, nor high CO/sub 2/ in combination with low O/sub 2/ caused significant perturbations of the sucrose/starch formation ratio. These studies indicate that the pathways for starch and sucrose synthesis both are controlled by the rate of net CO/sub 2/ assimilation, with sucrose the preferred product at very low assimilation rates.« less
  • Starch branching enzyme (SBE) activity in the cassava storage root exhibited a diurnal fluctuation, dictated by a transcriptional oscillation of the corresponding SBE genes. The peak of SBE activity coincided with the onset of sucrose accumulation in the storage, and we conclude that the oscillatory mechanism keeps the starch synthetic apparatus in the storage root sink in tune with the flux of sucrose from the photosynthetic source. When storage roots were uncoupled from the source, SBE expression could be effectively induced by exogenous sucrose. Turanose, a sucrose isomer that cannot be metabolized by plants, mimicked the effect of sucrose, demonstratingmore » that downstream metabolism of sucrose was not necessary for signal transmission. Also glucose and glucose-1-P induced SBE expression. Interestingly, induction by sucrose, turanose and glucose but not glucose-1-P sustained an overt semidian (12-h) oscillation in SBE expression and was sensitive to the hexokinase (HXK) inhibitor glucosamine. These results suggest a pivotal regulatory role for HXK during starch synthesis. Abscisic acid (ABA) was another potent inducer of SBE expression. Induction by ABA was similar to that of glucose-1-P in that it bypassed the semidian oscillator. Both the sugar and ABA signaling cascades were disrupted by okadaic acid, a protein phosphatase inhibitor. Based on these findings, we propose a model for sugar signaling in regulation of starch synthesis in the cassava storage root.« less
  • Etioplasts of 4.5-day-old dark-grown barley synthesize and accumulate most of the membrane and nearly all the soluble polypeptides of mature chloroplasts of light-grown seedlings. Etioplasts do not synthesize a limited set of chloroplast-encoded polypeptides which are major constituents of chloroplast thylakoid membranes: two chlorophyll apoproteins of photosystem I (68 and 65 kDa), two chlorophyll apoproteins of photosystem II (47 and 43 kDa), and a 32-kDa polypeptide which has now been identified as the psbA gene product. Throughout development in the dark, etioplasts were unable to synthesize the chlorophyll apoproteins of photosystem I and II or the psbA gene product despitemore » the presence of significant transcript levels for psbA and psaA-psaB (encode for photosystem I chlorophyll apoproteins). Light was not required for the synthesis of ribulose bisphosphate carboxylase large subunit with the highest rate of large subunit synthesis occurring in young dark-grown seedlings. Illumination of 4.5-day-old dark-grown barley rapidly induced the synthesis of the chlorophyll apoproteins and the psbA gene product at a time when transcript levels for psbA and psaA-psaB did not increase appreciably. Therefore, during the early stages of light-induced development the synthesis of the chlorophyll apoproteins of photosystem I and psbA gene product is regulated at the translational level. With continued chloroplast development in the light, the synthesis of the chlorophyll apoproteins of photosystem I and II decline rapidly as does the synthesis of the large subunit of ribulose bisphosphate carboxylase. The decline in polypeptide synthesis correlated with a decline in rbcL and psaA-psaB transcript levels and a light-dependent decline in plastid rRNA content. In contrast, synthesis of the psbA gene product was maintained throughout light-induced chloroplast development which correlated with the maintenance of psbA transcript levels. (Abstract Truncated)« less