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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.


Auxin response of CmF-308-transgenic tomato plants. (A) Primary root length of CmF-308-2 and control M-82 tomato seedlings after incubation in various concentrations of NAA. Seedlings were germinated on filter paper soaked in the auxin solutions in the dark. Lengths of primary roots were measured 10 days after germination. Data represent means of eight replications ± SE. Different letters indicate significant differences between auxin concentration treatments in each plant line Axillary at p < 0.05 by Tukey's HSD-test. (B) Auxin dose-response assay of cotyledon explants showing reduced auxin sensitivity in CmF308-2 cotyledons as compared to controls. Root regeneration is promoted by 0.1 μM NAA in the control variety and by 10 times higher concentration (1.0 μM NAA) in the transgenic line CmF-308-2. Pictures of representative plates were taken 12 days after placing the cut cotyledons on the various auxin media.
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Figure 7: Auxin response of CmF-308-transgenic tomato plants. (A) Primary root length of CmF-308-2 and control M-82 tomato seedlings after incubation in various concentrations of NAA. Seedlings were germinated on filter paper soaked in the auxin solutions in the dark. Lengths of primary roots were measured 10 days after germination. Data represent means of eight replications ± SE. Different letters indicate significant differences between auxin concentration treatments in each plant line Axillary at p < 0.05 by Tukey's HSD-test. (B) Auxin dose-response assay of cotyledon explants showing reduced auxin sensitivity in CmF308-2 cotyledons as compared to controls. Root regeneration is promoted by 0.1 μM NAA in the control variety and by 10 times higher concentration (1.0 μM NAA) in the transgenic line CmF-308-2. Pictures of representative plates were taken 12 days after placing the cut cotyledons on the various auxin media.

Mentions: The changes in lateral root and axillary shoot development suggested altered sensitivity to auxin in plants expressing CmF-308 under a phloem-specific promoter. We therefore examined the sensitivity of roots and shoots of transgenic and control plants to auxin. A dose-response assay revealed significant inhibition of primary root lengthening in CmF-308 plants at a concentration of 0.5 μM NAA, with no significant effect of this concentration on root length of control tomato plants (Figure 7A). This indicated that the roots of plants expressing the CmF-308 gene product are more sensitive to exogenous auxin than control roots. Primary root elongation of both control and CmF-308 plants was significantly inhibited by 1 μM NAA.


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)

Auxin response of CmF-308-transgenic tomato plants. (A) Primary root length of CmF-308-2 and control M-82 tomato seedlings after incubation in various concentrations of NAA. Seedlings were germinated on filter paper soaked in the auxin solutions in the dark. Lengths of primary roots were measured 10 days after germination. Data represent means of eight replications ± SE. Different letters indicate significant differences between auxin concentration treatments in each plant line Axillary at p < 0.05 by Tukey's HSD-test. (B) Auxin dose-response assay of cotyledon explants showing reduced auxin sensitivity in CmF308-2 cotyledons as compared to controls. Root regeneration is promoted by 0.1 μM NAA in the control variety and by 10 times higher concentration (1.0 μM NAA) in the transgenic line CmF-308-2. Pictures of representative plates were taken 12 days after placing the cut cotyledons on the various auxin media.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Auxin response of CmF-308-transgenic tomato plants. (A) Primary root length of CmF-308-2 and control M-82 tomato seedlings after incubation in various concentrations of NAA. Seedlings were germinated on filter paper soaked in the auxin solutions in the dark. Lengths of primary roots were measured 10 days after germination. Data represent means of eight replications ± SE. Different letters indicate significant differences between auxin concentration treatments in each plant line Axillary at p < 0.05 by Tukey's HSD-test. (B) Auxin dose-response assay of cotyledon explants showing reduced auxin sensitivity in CmF308-2 cotyledons as compared to controls. Root regeneration is promoted by 0.1 μM NAA in the control variety and by 10 times higher concentration (1.0 μM NAA) in the transgenic line CmF-308-2. Pictures of representative plates were taken 12 days after placing the cut cotyledons on the various auxin media.
Mentions: The changes in lateral root and axillary shoot development suggested altered sensitivity to auxin in plants expressing CmF-308 under a phloem-specific promoter. We therefore examined the sensitivity of roots and shoots of transgenic and control plants to auxin. A dose-response assay revealed significant inhibition of primary root lengthening in CmF-308 plants at a concentration of 0.5 μM NAA, with no significant effect of this concentration on root length of control tomato plants (Figure 7A). This indicated that the roots of plants expressing the CmF-308 gene product are more sensitive to exogenous auxin than control roots. Primary root elongation of both control and CmF-308 plants was significantly inhibited by 1 μM NAA.

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.