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The paramutated SULFUREA locus of tomato is involved in auxin biosynthesis.

Ehlert B, Schöttler MA, Tischendorf G, Ludwig-Müller J, Bock R - J. Exp. Bot. (2008)

Bottom Line: It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency.Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown.Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany.

ABSTRACT
The tomato (Solanum lycopersicum) sulfurea mutation displays trans-inactivation of wild-type alleles in heterozygous plants, a phenomenon referred to as paramutation. Homozygous mutant plants and paramutated leaf tissue of heterozygous plants show a pigment-deficient phenotype. The molecular basis of this phenotype and the function of the SULFUREA gene (SULF) are unknown. Here, a comprehensive physiological analysis of the sulfurea mutant is reported which suggests a molecular function for the SULFUREA locus. It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency. This is most strongly supported by the isolation of a suppressor mutant which shows an auxin overaccumulation phenotype and contains elevated levels of indole-3-acetic acid (IAA). Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown. Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis.

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Phenotype of the isolated SUPPRESSOR OF SULFUREA 1 (SOSU1) mutant. (A) Isolation of SOSU1 from a suppressor screen in tissue culture employing somaclonal variation. (B) Regeneration of SOSU1 plants from the green leaf sector. (C, D) Phenotypic comparison of a wild-type plant and a SOSU1 plant in sterile culture on sucrose-containing medium. Note that the suppressor mutant in (D) is approximately three times older than the wild-type plant in (C). (E, F) Phenotypic comparison of soil-grown wild-type (E) and SOSU1 (F) plants. (G, H) Close-up of leaves of the plants shown in (E) and (F). (I, J) Examples of mutant phenotypes of SOSU1 flowers showing multiple homeotic transformations of floral organs.
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fig6: Phenotype of the isolated SUPPRESSOR OF SULFUREA 1 (SOSU1) mutant. (A) Isolation of SOSU1 from a suppressor screen in tissue culture employing somaclonal variation. (B) Regeneration of SOSU1 plants from the green leaf sector. (C, D) Phenotypic comparison of a wild-type plant and a SOSU1 plant in sterile culture on sucrose-containing medium. Note that the suppressor mutant in (D) is approximately three times older than the wild-type plant in (C). (E, F) Phenotypic comparison of soil-grown wild-type (E) and SOSU1 (F) plants. (G, H) Close-up of leaves of the plants shown in (E) and (F). (I, J) Examples of mutant phenotypes of SOSU1 flowers showing multiple homeotic transformations of floral organs.

Mentions: Unlike most other epigenetic gene-silencing phenomena, gene inactivation by paramutation is not only somatically stable, but also heritable (Chandler et al., 2000; Chandler and Stam, 2004; Stam and Scheid, 2005; Bond and Finnegan, 2007; Chandler, 2007). To gain more insights into the mechanism of paramutation at the sulfurea locus and the involvement of SULF in auxin metabolism, a genetic screen for suppressors of the pale sulfurea phenotype was initiated. The establishment of an efficient shoot regeneration protocol for homozygous paramutated tissue (see the Materials and methods) allowed us to conduct such a suppressor screen by exposing sterile leaf explants to regeneration medium on a large scale. As tissue culture conditions themselves are mutagenic (a phenomenon also referred to as somaclonal variation), no additional mutagenesis treatment was done. In this screen, a mutant cell line was isolated that appeared as a dark green sector on a regenerating shoot (Fig. 6A). The sector was excised and uniformly green plantlets could be recovered by regeneration (Fig. 6B). Unlike the sulfurea mutant, these green plantlets were capable of growing in the absence of exogenously added auxin. However, they grew very slowly on synthetic medium (Fig. 6C, D) and were stunted, providing preliminary evidence for the mutant not being a revertant, but rather a suppressor of sulf.


The paramutated SULFUREA locus of tomato is involved in auxin biosynthesis.

Ehlert B, Schöttler MA, Tischendorf G, Ludwig-Müller J, Bock R - J. Exp. Bot. (2008)

Phenotype of the isolated SUPPRESSOR OF SULFUREA 1 (SOSU1) mutant. (A) Isolation of SOSU1 from a suppressor screen in tissue culture employing somaclonal variation. (B) Regeneration of SOSU1 plants from the green leaf sector. (C, D) Phenotypic comparison of a wild-type plant and a SOSU1 plant in sterile culture on sucrose-containing medium. Note that the suppressor mutant in (D) is approximately three times older than the wild-type plant in (C). (E, F) Phenotypic comparison of soil-grown wild-type (E) and SOSU1 (F) plants. (G, H) Close-up of leaves of the plants shown in (E) and (F). (I, J) Examples of mutant phenotypes of SOSU1 flowers showing multiple homeotic transformations of floral organs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2561159&req=5

fig6: Phenotype of the isolated SUPPRESSOR OF SULFUREA 1 (SOSU1) mutant. (A) Isolation of SOSU1 from a suppressor screen in tissue culture employing somaclonal variation. (B) Regeneration of SOSU1 plants from the green leaf sector. (C, D) Phenotypic comparison of a wild-type plant and a SOSU1 plant in sterile culture on sucrose-containing medium. Note that the suppressor mutant in (D) is approximately three times older than the wild-type plant in (C). (E, F) Phenotypic comparison of soil-grown wild-type (E) and SOSU1 (F) plants. (G, H) Close-up of leaves of the plants shown in (E) and (F). (I, J) Examples of mutant phenotypes of SOSU1 flowers showing multiple homeotic transformations of floral organs.
Mentions: Unlike most other epigenetic gene-silencing phenomena, gene inactivation by paramutation is not only somatically stable, but also heritable (Chandler et al., 2000; Chandler and Stam, 2004; Stam and Scheid, 2005; Bond and Finnegan, 2007; Chandler, 2007). To gain more insights into the mechanism of paramutation at the sulfurea locus and the involvement of SULF in auxin metabolism, a genetic screen for suppressors of the pale sulfurea phenotype was initiated. The establishment of an efficient shoot regeneration protocol for homozygous paramutated tissue (see the Materials and methods) allowed us to conduct such a suppressor screen by exposing sterile leaf explants to regeneration medium on a large scale. As tissue culture conditions themselves are mutagenic (a phenomenon also referred to as somaclonal variation), no additional mutagenesis treatment was done. In this screen, a mutant cell line was isolated that appeared as a dark green sector on a regenerating shoot (Fig. 6A). The sector was excised and uniformly green plantlets could be recovered by regeneration (Fig. 6B). Unlike the sulfurea mutant, these green plantlets were capable of growing in the absence of exogenously added auxin. However, they grew very slowly on synthetic medium (Fig. 6C, D) and were stunted, providing preliminary evidence for the mutant not being a revertant, but rather a suppressor of sulf.

Bottom Line: It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency.Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown.Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany.

ABSTRACT
The tomato (Solanum lycopersicum) sulfurea mutation displays trans-inactivation of wild-type alleles in heterozygous plants, a phenomenon referred to as paramutation. Homozygous mutant plants and paramutated leaf tissue of heterozygous plants show a pigment-deficient phenotype. The molecular basis of this phenotype and the function of the SULFUREA gene (SULF) are unknown. Here, a comprehensive physiological analysis of the sulfurea mutant is reported which suggests a molecular function for the SULFUREA locus. It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency. This is most strongly supported by the isolation of a suppressor mutant which shows an auxin overaccumulation phenotype and contains elevated levels of indole-3-acetic acid (IAA). Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown. Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis.

Show MeSH
Related in: MedlinePlus