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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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Growth characteristics of controls and mutant plants complemented with promoter::cSUC2 cassettes. A, Rosette area (cm2) of 21-day old wild type (AtSUC2 +/+), heterozygous (AtSUC2 +/-), homozygous mutant (AtSUC2 -/-), and homozygous mutant plants independently transformed (indicated by seed-stock number) with the indicated cSUC2 constructs; n = 4 to 10 sibling plants. Lines marked * are homozygous for the promoter::cSUC2 cassettes, and from these, a representative line for each was chosen for further analysis. B to D, representative 21-day old AtSUC2 +/+, AtSUC2 +/-, and AtSUC2 -/- plants, respectively. E to H, Representative 21-day old AtSUC2 -/- plants transformed with SUC2p::cSUC2::uidA (E; line 1042) SUC2p::cSUC2 (F; line 1039), CoYMVp::cSUC2 (G; line 1070), and rolCp::cSUC2 (H; line 1133) constructs. Scale bar, B through H = 1 cm. I to L, XGlcA staining in source leaves of untransformed wild type (I), and heterozygous AtSUC2 +/- plants transformed with SUC2p::cSUC2::uidA (J), CoYMVp::cSUC2::uidA (K), and rolCp::cSUC2::uidA (L). The staining pattern was the same irrespective of zygosity at the AtSUC2 locus. Scale bar, I through L = 1 mm.
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Figure 2: Growth characteristics of controls and mutant plants complemented with promoter::cSUC2 cassettes. A, Rosette area (cm2) of 21-day old wild type (AtSUC2 +/+), heterozygous (AtSUC2 +/-), homozygous mutant (AtSUC2 -/-), and homozygous mutant plants independently transformed (indicated by seed-stock number) with the indicated cSUC2 constructs; n = 4 to 10 sibling plants. Lines marked * are homozygous for the promoter::cSUC2 cassettes, and from these, a representative line for each was chosen for further analysis. B to D, representative 21-day old AtSUC2 +/+, AtSUC2 +/-, and AtSUC2 -/- plants, respectively. E to H, Representative 21-day old AtSUC2 -/- plants transformed with SUC2p::cSUC2::uidA (E; line 1042) SUC2p::cSUC2 (F; line 1039), CoYMVp::cSUC2 (G; line 1070), and rolCp::cSUC2 (H; line 1133) constructs. Scale bar, B through H = 1 cm. I to L, XGlcA staining in source leaves of untransformed wild type (I), and heterozygous AtSUC2 +/- plants transformed with SUC2p::cSUC2::uidA (J), CoYMVp::cSUC2::uidA (K), and rolCp::cSUC2::uidA (L). The staining pattern was the same irrespective of zygosity at the AtSUC2 locus. Scale bar, I through L = 1 mm.

Mentions: The independent transformants demonstrated a range of growth, presumably reflecting differing levels of cSUC2 cDNA expression. Growth of eight independent lines for each construct is presented in Fig. 2A to show the range of complementation obtained. Those marked (*) were homozygous for the cDNA based on 100% resistance to glufosinate ammonia among seedlings (n > 16). The remainder had sensitive seedlings, showing they were still segregating for the cDNA in the generation used (T3 or T4), and the plants measured may have been hemizygous or homozygous for the transgene. Those harboring the promoter::cSUC2::uidA cassettes demonstrated poor growth, indicating that the β-glucuronidase fusion compromised AtSUC2 activity, but performed slightly better than the AtSUC2 -/- parent line (Fig. 2A, D, E), implying some activity in planta. β-Glucuronidase activity was not compromised, however, and these lines confirmed the expression patterns conferred by the promoters. Growth of plants with the promoter::cSUC::GFP cassettes was intermediate between cSUC2 plants and cSUC2::uidA plants (not shown), suggesting that AtSUC2 is somewhat tolerant of fusions proteins, but these GFP constructs were still not suited for complementation assays and were not pursued.


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)

Growth characteristics of controls and mutant plants complemented with promoter::cSUC2 cassettes. A, Rosette area (cm2) of 21-day old wild type (AtSUC2 +/+), heterozygous (AtSUC2 +/-), homozygous mutant (AtSUC2 -/-), and homozygous mutant plants independently transformed (indicated by seed-stock number) with the indicated cSUC2 constructs; n = 4 to 10 sibling plants. Lines marked * are homozygous for the promoter::cSUC2 cassettes, and from these, a representative line for each was chosen for further analysis. B to D, representative 21-day old AtSUC2 +/+, AtSUC2 +/-, and AtSUC2 -/- plants, respectively. E to H, Representative 21-day old AtSUC2 -/- plants transformed with SUC2p::cSUC2::uidA (E; line 1042) SUC2p::cSUC2 (F; line 1039), CoYMVp::cSUC2 (G; line 1070), and rolCp::cSUC2 (H; line 1133) constructs. Scale bar, B through H = 1 cm. I to L, XGlcA staining in source leaves of untransformed wild type (I), and heterozygous AtSUC2 +/- plants transformed with SUC2p::cSUC2::uidA (J), CoYMVp::cSUC2::uidA (K), and rolCp::cSUC2::uidA (L). The staining pattern was the same irrespective of zygosity at the AtSUC2 locus. Scale bar, I through L = 1 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Growth characteristics of controls and mutant plants complemented with promoter::cSUC2 cassettes. A, Rosette area (cm2) of 21-day old wild type (AtSUC2 +/+), heterozygous (AtSUC2 +/-), homozygous mutant (AtSUC2 -/-), and homozygous mutant plants independently transformed (indicated by seed-stock number) with the indicated cSUC2 constructs; n = 4 to 10 sibling plants. Lines marked * are homozygous for the promoter::cSUC2 cassettes, and from these, a representative line for each was chosen for further analysis. B to D, representative 21-day old AtSUC2 +/+, AtSUC2 +/-, and AtSUC2 -/- plants, respectively. E to H, Representative 21-day old AtSUC2 -/- plants transformed with SUC2p::cSUC2::uidA (E; line 1042) SUC2p::cSUC2 (F; line 1039), CoYMVp::cSUC2 (G; line 1070), and rolCp::cSUC2 (H; line 1133) constructs. Scale bar, B through H = 1 cm. I to L, XGlcA staining in source leaves of untransformed wild type (I), and heterozygous AtSUC2 +/- plants transformed with SUC2p::cSUC2::uidA (J), CoYMVp::cSUC2::uidA (K), and rolCp::cSUC2::uidA (L). The staining pattern was the same irrespective of zygosity at the AtSUC2 locus. Scale bar, I through L = 1 mm.
Mentions: The independent transformants demonstrated a range of growth, presumably reflecting differing levels of cSUC2 cDNA expression. Growth of eight independent lines for each construct is presented in Fig. 2A to show the range of complementation obtained. Those marked (*) were homozygous for the cDNA based on 100% resistance to glufosinate ammonia among seedlings (n > 16). The remainder had sensitive seedlings, showing they were still segregating for the cDNA in the generation used (T3 or T4), and the plants measured may have been hemizygous or homozygous for the transgene. Those harboring the promoter::cSUC2::uidA cassettes demonstrated poor growth, indicating that the β-glucuronidase fusion compromised AtSUC2 activity, but performed slightly better than the AtSUC2 -/- parent line (Fig. 2A, D, E), implying some activity in planta. β-Glucuronidase activity was not compromised, however, and these lines confirmed the expression patterns conferred by the promoters. Growth of plants with the promoter::cSUC::GFP cassettes was intermediate between cSUC2 plants and cSUC2::uidA plants (not shown), suggesting that AtSUC2 is somewhat tolerant of fusions proteins, but these GFP constructs were still not suited for complementation assays and were not pursued.

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