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Phloem-specific expression of a melon Aux/IAA in tomato plants alters auxin sensitivity and plant development.

Golan G, Betzer R, Wolf S - Front Plant Sci (2013)

Bottom Line: A similar effect on root development was obtained after transient expression of CmF-308 in source leaves of N. benthamiana plants.In addition to the altered root development, phloem-specific expression of CmF-308 resulted in shorter plants, a higher number of lateral shoots and delayed flowering, a phenotype resembling reduced apical dominance.The reduced auxin sensitivity in the shoot tissue was confirmed by lower relative expression of several Aux/IAA genes in leaves and an increase in the relative expression of a cytokinin-response regulator, TRR8/9b.

View Article: PubMed Central - PubMed

Affiliation: The Robert H. Smith Faculty of Agriculture, Food and Environment, Otto Warburg Minerva Center for Agricultural Biotechnology, The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem Rehovot, Israel.

ABSTRACT
Phloem sap contains a large repertoire of macromolecules in addition to sugars, amino acids, growth substances and ions. The transcription profile of melon phloem sap contains over 1000 mRNA molecules, most of them associated with signal transduction, transcriptional control, and stress and defense responses. Heterografting experiments have established the long-distance trafficking of numerous mRNA molecules. Interestingly, several trafficking transcripts are involved in the auxin response, including two molecules coding for auxin/indole acetic acid (Aux/IAA). To further explore the biological role of the melon Aux/IAA transcript CmF-308 in the vascular tissue, a cassette containing the coding sequence of this gene under a phloem-specific promoter was introduced into tomato plants. The number of lateral roots was significantly higher in transgenic plants expressing CmF-308 under the AtSUC2 promoter than in controls. A similar effect on root development was obtained after transient expression of CmF-308 in source leaves of N. benthamiana plants. An auxin-response assay showed that CmF-308-transgenic roots are more sensitive to auxin than control roots. In addition to the altered root development, phloem-specific expression of CmF-308 resulted in shorter plants, a higher number of lateral shoots and delayed flowering, a phenotype resembling reduced apical dominance. In contrast to the root response, cotyledons of the transgenic plants were less sensitive to auxin than control cotyledons. The reduced auxin sensitivity in the shoot tissue was confirmed by lower relative expression of several Aux/IAA genes in leaves and an increase in the relative expression of a cytokinin-response regulator, TRR8/9b. The accumulated data suggest that expression of Aux/IAA in the phloem modifies auxin sensitivity in a tissue-specific manner, thereby altering plant development.

No MeSH data available.


Effect of CmF-308 expression in the phloem of tomato plants on root development. Number of lateral roots (A), root dry weight (B), and a picture (C) presenting the differences between roots of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. (D) Shoot dry weight of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. Lateral roots were counted in 9-days old seedlings germination on germination papers (A). Shoot and root weight was measured in 3-week old pot-grown plants (B–D). Data represent means of six replications ± SE. Different letters indicate significant differences between the plant lines at p < 0.05 by Student's t-test.
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Figure 5: Effect of CmF-308 expression in the phloem of tomato plants on root development. Number of lateral roots (A), root dry weight (B), and a picture (C) presenting the differences between roots of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. (D) Shoot dry weight of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. Lateral roots were counted in 9-days old seedlings germination on germination papers (A). Shoot and root weight was measured in 3-week old pot-grown plants (B–D). Data represent means of six replications ± SE. Different letters indicate significant differences between the plant lines at p < 0.05 by Student's t-test.

Mentions: To further explore the effect of phloem-limited expression of CmF-308 on plant development, the gene's coding sequence was inserted into transgenic tomato plants under the control of the phloem specific AtSUC2 promoter (Shalit et al., 2009). Activity of the AtSUC2 promoter, as phloem specific promoter in tomatoes was verified using GFP as a reporter protein (Figure 4A). In agreement with the activity of AtSUC2 promoter along the vasculature, CmF-308 was expressed in the shoot apices and roots of the transgenic tomato plants (Figure 4B). Over ten independent homozygous CmF-308-transgenic tomato plants were generated. Most of them had similar phenotype and two representative lines were selected for further study. Similar to the effect observed after transient expression, constitutive expression of CmF-308 in the phloem of tomato plants caused a significant increase in the number of lateral roots and root weight (Figures 5A–C). Note that shoot weight was similar in CmF-308 and control tomato plants (Figure 5D).


Phloem-specific expression of a melon Aux/IAA in tomato plants alters auxin sensitivity and plant development.

Golan G, Betzer R, Wolf S - Front Plant Sci (2013)

Effect of CmF-308 expression in the phloem of tomato plants on root development. Number of lateral roots (A), root dry weight (B), and a picture (C) presenting the differences between roots of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. (D) Shoot dry weight of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. Lateral roots were counted in 9-days old seedlings germination on germination papers (A). Shoot and root weight was measured in 3-week old pot-grown plants (B–D). Data represent means of six replications ± SE. Different letters indicate significant differences between the plant lines at p < 0.05 by Student's t-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750518&req=5

Figure 5: Effect of CmF-308 expression in the phloem of tomato plants on root development. Number of lateral roots (A), root dry weight (B), and a picture (C) presenting the differences between roots of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. (D) Shoot dry weight of transgenic tomato plants expressing CmF-308 under the AtSUC2 promoter (CmF-308-2) as compared with the control variety M-82. Lateral roots were counted in 9-days old seedlings germination on germination papers (A). Shoot and root weight was measured in 3-week old pot-grown plants (B–D). Data represent means of six replications ± SE. Different letters indicate significant differences between the plant lines at p < 0.05 by Student's t-test.
Mentions: To further explore the effect of phloem-limited expression of CmF-308 on plant development, the gene's coding sequence was inserted into transgenic tomato plants under the control of the phloem specific AtSUC2 promoter (Shalit et al., 2009). Activity of the AtSUC2 promoter, as phloem specific promoter in tomatoes was verified using GFP as a reporter protein (Figure 4A). In agreement with the activity of AtSUC2 promoter along the vasculature, CmF-308 was expressed in the shoot apices and roots of the transgenic tomato plants (Figure 4B). Over ten independent homozygous CmF-308-transgenic tomato plants were generated. Most of them had similar phenotype and two representative lines were selected for further study. Similar to the effect observed after transient expression, constitutive expression of CmF-308 in the phloem of tomato plants caused a significant increase in the number of lateral roots and root weight (Figures 5A–C). Note that shoot weight was similar in CmF-308 and control tomato plants (Figure 5D).

Bottom Line: A similar effect on root development was obtained after transient expression of CmF-308 in source leaves of N. benthamiana plants.In addition to the altered root development, phloem-specific expression of CmF-308 resulted in shorter plants, a higher number of lateral shoots and delayed flowering, a phenotype resembling reduced apical dominance.The reduced auxin sensitivity in the shoot tissue was confirmed by lower relative expression of several Aux/IAA genes in leaves and an increase in the relative expression of a cytokinin-response regulator, TRR8/9b.

View Article: PubMed Central - PubMed

Affiliation: The Robert H. Smith Faculty of Agriculture, Food and Environment, Otto Warburg Minerva Center for Agricultural Biotechnology, The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem Rehovot, Israel.

ABSTRACT
Phloem sap contains a large repertoire of macromolecules in addition to sugars, amino acids, growth substances and ions. The transcription profile of melon phloem sap contains over 1000 mRNA molecules, most of them associated with signal transduction, transcriptional control, and stress and defense responses. Heterografting experiments have established the long-distance trafficking of numerous mRNA molecules. Interestingly, several trafficking transcripts are involved in the auxin response, including two molecules coding for auxin/indole acetic acid (Aux/IAA). To further explore the biological role of the melon Aux/IAA transcript CmF-308 in the vascular tissue, a cassette containing the coding sequence of this gene under a phloem-specific promoter was introduced into tomato plants. The number of lateral roots was significantly higher in transgenic plants expressing CmF-308 under the AtSUC2 promoter than in controls. A similar effect on root development was obtained after transient expression of CmF-308 in source leaves of N. benthamiana plants. An auxin-response assay showed that CmF-308-transgenic roots are more sensitive to auxin than control roots. In addition to the altered root development, phloem-specific expression of CmF-308 resulted in shorter plants, a higher number of lateral shoots and delayed flowering, a phenotype resembling reduced apical dominance. In contrast to the root response, cotyledons of the transgenic plants were less sensitive to auxin than control cotyledons. The reduced auxin sensitivity in the shoot tissue was confirmed by lower relative expression of several Aux/IAA genes in leaves and an increase in the relative expression of a cytokinin-response regulator, TRR8/9b. The accumulated data suggest that expression of Aux/IAA in the phloem modifies auxin sensitivity in a tissue-specific manner, thereby altering plant development.

No MeSH data available.