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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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Semi-quantitative RT-PCR of AtSUC2 and cSUC2 transcripts in wild type and experimental lines, relative to UBQ10 transcript (encoding ubiquitin). RNA was isolated from two pools of each line 14 days after germination and cDNA created by reverse transcription. Semi-quantitative PCR was performed in duplicate, and transcript levels expressed relative to UBQ10 transcript abundance. Variation is expressed as standard deviation among duplicates.
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Figure 3: Semi-quantitative RT-PCR of AtSUC2 and cSUC2 transcripts in wild type and experimental lines, relative to UBQ10 transcript (encoding ubiquitin). RNA was isolated from two pools of each line 14 days after germination and cDNA created by reverse transcription. Semi-quantitative PCR was performed in duplicate, and transcript levels expressed relative to UBQ10 transcript abundance. Variation is expressed as standard deviation among duplicates.

Mentions: The average rosette area for the four most robust SUC2p::cSUC2 transformants was not significantly different from heterozygous plants (Fig. 2, Table 1) [25]. From these four robust lines that most closely mimicked wild type growth, a single line that was homozygous for the transgene was selected as a representative line for further study (Fig. 2F; line 1039). Two weeks after germination, cSUC2 transcript abundance in whole rosettes of line 1039 plants, relative to UBQ10 transcript as an internal standard [37], was very similar to that observed in AtSUC2 +/+ plants (Fig 3). Three weeks after germination, rosette growth in line 1039 was not significantly different from AtSUC2 +/+ or AtSUC2 +/- plants (Table 1). Root growth in line 1039 was not significantly different from wild type roots 16 days after germination on sterile MS media with 0% Suc (Table 1). A representative SUC2p::cSUC2::uidA leaf stained with XGlcA is shown in Fig. 2J, demonstrating staining only in the vascular tissue of mature leaves. In immature leaves, the staining pattern was characteristic of the sink-to-source transition, as previously described [7,36]. None of the 12 SUC2p::cSUC2::uidA lines analyzed deviated from this pattern (not shown).


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)

Semi-quantitative RT-PCR of AtSUC2 and cSUC2 transcripts in wild type and experimental lines, relative to UBQ10 transcript (encoding ubiquitin). RNA was isolated from two pools of each line 14 days after germination and cDNA created by reverse transcription. Semi-quantitative PCR was performed in duplicate, and transcript levels expressed relative to UBQ10 transcript abundance. Variation is expressed as standard deviation among duplicates.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Semi-quantitative RT-PCR of AtSUC2 and cSUC2 transcripts in wild type and experimental lines, relative to UBQ10 transcript (encoding ubiquitin). RNA was isolated from two pools of each line 14 days after germination and cDNA created by reverse transcription. Semi-quantitative PCR was performed in duplicate, and transcript levels expressed relative to UBQ10 transcript abundance. Variation is expressed as standard deviation among duplicates.
Mentions: The average rosette area for the four most robust SUC2p::cSUC2 transformants was not significantly different from heterozygous plants (Fig. 2, Table 1) [25]. From these four robust lines that most closely mimicked wild type growth, a single line that was homozygous for the transgene was selected as a representative line for further study (Fig. 2F; line 1039). Two weeks after germination, cSUC2 transcript abundance in whole rosettes of line 1039 plants, relative to UBQ10 transcript as an internal standard [37], was very similar to that observed in AtSUC2 +/+ plants (Fig 3). Three weeks after germination, rosette growth in line 1039 was not significantly different from AtSUC2 +/+ or AtSUC2 +/- plants (Table 1). Root growth in line 1039 was not significantly different from wild type roots 16 days after germination on sterile MS media with 0% Suc (Table 1). A representative SUC2p::cSUC2::uidA leaf stained with XGlcA is shown in Fig. 2J, demonstrating staining only in the vascular tissue of mature leaves. In immature leaves, the staining pattern was characteristic of the sink-to-source transition, as previously described [7,36]. None of the 12 SUC2p::cSUC2::uidA lines analyzed deviated from this pattern (not shown).

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