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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.


Relative expression levels of CmF-308, as determined by real-time RT-PCR. Relative expression was compared in various melon plant organs (A), in veins and leaf lamina (B) and in mesophyll and vascular bundle cells isolated by laser-capture microdissection system (C). Leaf discs and single cells were collected from the youngest mature source leaf (no. 4). Data represent means of three to six replications (±SE). Different letters indicate significant differences between plant organs or cell types at p < 0.05 by Tukey's HSD-test.
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Figure 1: Relative expression levels of CmF-308, as determined by real-time RT-PCR. Relative expression was compared in various melon plant organs (A), in veins and leaf lamina (B) and in mesophyll and vascular bundle cells isolated by laser-capture microdissection system (C). Leaf discs and single cells were collected from the youngest mature source leaf (no. 4). Data represent means of three to six replications (±SE). Different letters indicate significant differences between plant organs or cell types at p < 0.05 by Tukey's HSD-test.

Mentions: Following our finding that the melon phloem-sap transcript CmF-308 is capable of long-distance trafficking, our initial set of experiments was aimed at identifying its level of accumulation in various tissues of melon plants. Quantitative (q) RT-PCR analyses revealed highest relative expression of this transcript in the hypocotyls and stems of young melon seedlings, with significantly lower relative expression in roots, leaves and shoot apices (Figure 1A). To further verify that CmF-308 accumulates in tissues enriched with vascular bundles, veins were separated from young mature leaves. Here again, relative expression of CmF-308 in the veins was three times higher than that in the rest of the leaf (Figure 1B). Predominant accumulation of CmF-308 in vascular cells was confirmed by collection of specific cell types using the laser-capture microdissection system (Figure 1C).


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)

Relative expression levels of CmF-308, as determined by real-time RT-PCR. Relative expression was compared in various melon plant organs (A), in veins and leaf lamina (B) and in mesophyll and vascular bundle cells isolated by laser-capture microdissection system (C). Leaf discs and single cells were collected from the youngest mature source leaf (no. 4). Data represent means of three to six replications (±SE). Different letters indicate significant differences between plant organs or cell types at p < 0.05 by Tukey's HSD-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Relative expression levels of CmF-308, as determined by real-time RT-PCR. Relative expression was compared in various melon plant organs (A), in veins and leaf lamina (B) and in mesophyll and vascular bundle cells isolated by laser-capture microdissection system (C). Leaf discs and single cells were collected from the youngest mature source leaf (no. 4). Data represent means of three to six replications (±SE). Different letters indicate significant differences between plant organs or cell types at p < 0.05 by Tukey's HSD-test.
Mentions: Following our finding that the melon phloem-sap transcript CmF-308 is capable of long-distance trafficking, our initial set of experiments was aimed at identifying its level of accumulation in various tissues of melon plants. Quantitative (q) RT-PCR analyses revealed highest relative expression of this transcript in the hypocotyls and stems of young melon seedlings, with significantly lower relative expression in roots, leaves and shoot apices (Figure 1A). To further verify that CmF-308 accumulates in tissues enriched with vascular bundles, veins were separated from young mature leaves. Here again, relative expression of CmF-308 in the veins was three times higher than that in the rest of the leaf (Figure 1B). Predominant accumulation of CmF-308 in vascular cells was confirmed by collection of specific cell types using the laser-capture microdissection system (Figure 1C).

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.