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Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene.

Srivastava AC, Ganesan S, Ismail IO, Ayre BG - BMC Plant Biol. (2009)

Bottom Line: CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation.Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport.Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of North Texas, Department of Biological Sciences, PO Box 305220, Denton, TX 76203-5220, USA. acsrivastava@noble.org

ABSTRACT

Background: AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink to source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones.

Results: To assess the importance of this regulation to whole-plant growth and carbon partitioning, AtSUC2 cDNA was expressed from two exotic, phloem-specific promoters in a mutant background debilitated for AtSUC2 function. The first was a promoter element from Commelina Yellow Mottle Virus (CoYMV), and the second was the rolC promoter from Agrobacterium rhizogenes. CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation.

Conclusion: Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport. Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology.

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Autoradiography showing accumulation of [14C]-Suc in whole rosettes. A through H, Representative rosette and individual leaf from a wild type plant (A, B) and lines 1039 (C, D), 1070 (E, F), and 1133 (G, H), respectively. Black arrowheads point to a mature source leaf with 14C accumulation in the veins and clearing from the areoles, white arrowheads point to sink leaves with diffuse labeling throughout the lamina, and grey arrowheads point to transition leaves. I and J, A representative homozygous SALK_038124 (AtSUC2 -/-) plant showing modest 14C accumulation only in putative sink regions of sink and transition leaves. Dark areas of the autoradiographs labeled (*) are artifacts of the adhesive used to secure the lyophilized tissue to a cardboard support in preparation for exposure to the X-ray film. The leaf directed to the top of the figure in A, C, E, G and I is magnified in B, D, F, H, and J; Scale bars, 5 mm in A, C, E, G and I 1 mm in B, D, F, H, and J.
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Figure 5: Autoradiography showing accumulation of [14C]-Suc in whole rosettes. A through H, Representative rosette and individual leaf from a wild type plant (A, B) and lines 1039 (C, D), 1070 (E, F), and 1133 (G, H), respectively. Black arrowheads point to a mature source leaf with 14C accumulation in the veins and clearing from the areoles, white arrowheads point to sink leaves with diffuse labeling throughout the lamina, and grey arrowheads point to transition leaves. I and J, A representative homozygous SALK_038124 (AtSUC2 -/-) plant showing modest 14C accumulation only in putative sink regions of sink and transition leaves. Dark areas of the autoradiographs labeled (*) are artifacts of the adhesive used to secure the lyophilized tissue to a cardboard support in preparation for exposure to the X-ray film. The leaf directed to the top of the figure in A, C, E, G and I is magnified in B, D, F, H, and J; Scale bars, 5 mm in A, C, E, G and I 1 mm in B, D, F, H, and J.

Mentions: To analyze Suc uptake in transgenic and control plants, rosettes were excised from the plant and infiltrated with a buffered solution of [14C]-Suc and incubated for 20 minutes. After thorough washing, two replicates were subjected to scintillation counting to quantify uptake (Fig. 4), and a third replicate was subjected to autoradiography to identify sites of [14C] accumulation (Fig. 5). Leaves from wild type controls (AtSUC2 +/+) and from the representative AtSUC -/- lines, 1039 (SUC2p::cSUC2), 1070 (CoYMVp::cSUC2), and 1133 (rolC::cSUC2) accumulated [14C] to similar levels, irrespective of differences in SUC2 transcript abundance, growth, and transient carbohydrate levels (Fig 4A). In addition, all showed label accumulation in the veins and clearing from interveinal tissues (areoles) of mature leaves (Fig. 5A–H). Label was distributed throughout the lamina of small sink leaves, and midsize leaves demonstrated vein labeling in distal portions and diffuse labeling in proximal regions of the leaves. The size and labeling pattern of these leaves strongly suggests that they are transition leaves, with distal regions loading and exporting sugar as source tissue, and proximal regions importing nutrients as sink tissue.


Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene.

Srivastava AC, Ganesan S, Ismail IO, Ayre BG - BMC Plant Biol. (2009)

Autoradiography showing accumulation of [14C]-Suc in whole rosettes. A through H, Representative rosette and individual leaf from a wild type plant (A, B) and lines 1039 (C, D), 1070 (E, F), and 1133 (G, H), respectively. Black arrowheads point to a mature source leaf with 14C accumulation in the veins and clearing from the areoles, white arrowheads point to sink leaves with diffuse labeling throughout the lamina, and grey arrowheads point to transition leaves. I and J, A representative homozygous SALK_038124 (AtSUC2 -/-) plant showing modest 14C accumulation only in putative sink regions of sink and transition leaves. Dark areas of the autoradiographs labeled (*) are artifacts of the adhesive used to secure the lyophilized tissue to a cardboard support in preparation for exposure to the X-ray film. The leaf directed to the top of the figure in A, C, E, G and I is magnified in B, D, F, H, and J; Scale bars, 5 mm in A, C, E, G and I 1 mm in B, D, F, H, and J.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2654897&req=5

Figure 5: Autoradiography showing accumulation of [14C]-Suc in whole rosettes. A through H, Representative rosette and individual leaf from a wild type plant (A, B) and lines 1039 (C, D), 1070 (E, F), and 1133 (G, H), respectively. Black arrowheads point to a mature source leaf with 14C accumulation in the veins and clearing from the areoles, white arrowheads point to sink leaves with diffuse labeling throughout the lamina, and grey arrowheads point to transition leaves. I and J, A representative homozygous SALK_038124 (AtSUC2 -/-) plant showing modest 14C accumulation only in putative sink regions of sink and transition leaves. Dark areas of the autoradiographs labeled (*) are artifacts of the adhesive used to secure the lyophilized tissue to a cardboard support in preparation for exposure to the X-ray film. The leaf directed to the top of the figure in A, C, E, G and I is magnified in B, D, F, H, and J; Scale bars, 5 mm in A, C, E, G and I 1 mm in B, D, F, H, and J.
Mentions: To analyze Suc uptake in transgenic and control plants, rosettes were excised from the plant and infiltrated with a buffered solution of [14C]-Suc and incubated for 20 minutes. After thorough washing, two replicates were subjected to scintillation counting to quantify uptake (Fig. 4), and a third replicate was subjected to autoradiography to identify sites of [14C] accumulation (Fig. 5). Leaves from wild type controls (AtSUC2 +/+) and from the representative AtSUC -/- lines, 1039 (SUC2p::cSUC2), 1070 (CoYMVp::cSUC2), and 1133 (rolC::cSUC2) accumulated [14C] to similar levels, irrespective of differences in SUC2 transcript abundance, growth, and transient carbohydrate levels (Fig 4A). In addition, all showed label accumulation in the veins and clearing from interveinal tissues (areoles) of mature leaves (Fig. 5A–H). Label was distributed throughout the lamina of small sink leaves, and midsize leaves demonstrated vein labeling in distal portions and diffuse labeling in proximal regions of the leaves. The size and labeling pattern of these leaves strongly suggests that they are transition leaves, with distal regions loading and exporting sugar as source tissue, and proximal regions importing nutrients as sink tissue.

Bottom Line: CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation.Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport.Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of North Texas, Department of Biological Sciences, PO Box 305220, Denton, TX 76203-5220, USA. acsrivastava@noble.org

ABSTRACT

Background: AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink to source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones.

Results: To assess the importance of this regulation to whole-plant growth and carbon partitioning, AtSUC2 cDNA was expressed from two exotic, phloem-specific promoters in a mutant background debilitated for AtSUC2 function. The first was a promoter element from Commelina Yellow Mottle Virus (CoYMV), and the second was the rolC promoter from Agrobacterium rhizogenes. CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation.

Conclusion: Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport. Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology.

Show MeSH
Related in: MedlinePlus