Limits...
SRD1 is involved in the auxin-mediated initial thickening growth of storage root by enhancing proliferation of metaxylem and cambium cells in sweetpotato (Ipomoea batatas).

Noh SA, Lee HS, Huh EJ, Huh GH, Paek KH, Shin JS, Bae JM - J. Exp. Bot. (2010)

Bottom Line: SRD1 mRNA was mainly found in the actively dividing cells, including the vascular and cambium cells of the young storage root.During the early stage of storage root development, the endogenous IAA content and SRD1 transcript level increased concomitantly, suggesting an involvement of SRD1 during the early stage of the auxin-dependent development of the storage root.Taken together, these results demonstrate that SRD1 plays a role in the formation of storage roots by activating the proliferation of cambium and metaxylem cells to induce the initial thickening growth of storage roots in an auxin-dependent manner.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea.

ABSTRACT
A sweetpotato (Ipomoea batatas cv. 'Jinhongmi') MADS-box protein cDNA (SRD1) has been isolated from an early stage storage root cDNA library. The role of the SRD1 gene in the formation of the storage root in sweetpotato was investigated by an expression pattern analysis and characterization of SRD1-overexpressing (ox) transgenic sweetpotato plants. Transcripts of SRD1 were detected only in root tissues, with the fibrous root having low levels of the transcript and the young storage root showing relatively higher transcript levels. SRD1 mRNA was mainly found in the actively dividing cells, including the vascular and cambium cells of the young storage root. The transcript level of SRD1 in the fibrous roots increased in response to 1000 muM indole-3-acetic acid (IAA) applied exogenously. During the early stage of storage root development, the endogenous IAA content and SRD1 transcript level increased concomitantly, suggesting an involvement of SRD1 during the early stage of the auxin-dependent development of the storage root. SRD1-ox sweetpotato plants cultured in vitro produced thicker and shorter fibrous roots than wild-type plants. The metaxylem and cambium cells of the fibrous roots of SRD1-ox plants showed markedly enhanced proliferation, resulting in the fibrous roots of these plants showing an earlier thickening growth than those of wild-type plants. Taken together, these results demonstrate that SRD1 plays a role in the formation of storage roots by activating the proliferation of cambium and metaxylem cells to induce the initial thickening growth of storage roots in an auxin-dependent manner.

Show MeSH

Related in: MedlinePlus

Characterization of SRD1-ox sweetpotato plants. (A) SRD1 transcript levels in SRD1-ox plants. Total RNA was isolated from fibrous root tissue of the sweetpotato plants cultured in vitro. Semi-quantitative RT-PCR analysis was conducted with SRD1-specific primers. Numbers 1–5 represent SRD1-ox sweetpotato lines 1–5. Sweetpotato β-tubulin was used as an equal loading internal control. WT, wild-type. (B) Morphology of the fibrous roots in SRD1-ox plants. Pictures were taken from the bottom of the culture plate for a better view of the root morphology. (C) Microscopic observation of the transverse section of fibrous root in the area marked with a box in B. The lower panel is an enlarged image of the upper panel. MPH, metaphloem; MX, metaxylem; PC, primary cambium; SC, secondary cambium; PXY, protoxylem. (D) Quantitative characterization of fibrous root development in SRD1-ox lines 1 and 3. Data were collected from the sweetpotato plants cultured in vitro at 14 d after planting and are the means±SD from three separate measurements of three individual plants. Root diameter and cell numbers were measured on transverse sections of fibrous roots. Root diameter was determined by measuring the largest diameter on the circle enclosed by epidermal cells. Numbers of metaxylem cells include numbers of mature and immature metaxylem cells. For determination of cell numbers and root diameters, three cell files from three individual plants were used. WT, wild-type. (This figure is available in colour at JXB online.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2837253&req=5

fig7: Characterization of SRD1-ox sweetpotato plants. (A) SRD1 transcript levels in SRD1-ox plants. Total RNA was isolated from fibrous root tissue of the sweetpotato plants cultured in vitro. Semi-quantitative RT-PCR analysis was conducted with SRD1-specific primers. Numbers 1–5 represent SRD1-ox sweetpotato lines 1–5. Sweetpotato β-tubulin was used as an equal loading internal control. WT, wild-type. (B) Morphology of the fibrous roots in SRD1-ox plants. Pictures were taken from the bottom of the culture plate for a better view of the root morphology. (C) Microscopic observation of the transverse section of fibrous root in the area marked with a box in B. The lower panel is an enlarged image of the upper panel. MPH, metaphloem; MX, metaxylem; PC, primary cambium; SC, secondary cambium; PXY, protoxylem. (D) Quantitative characterization of fibrous root development in SRD1-ox lines 1 and 3. Data were collected from the sweetpotato plants cultured in vitro at 14 d after planting and are the means±SD from three separate measurements of three individual plants. Root diameter and cell numbers were measured on transverse sections of fibrous roots. Root diameter was determined by measuring the largest diameter on the circle enclosed by epidermal cells. Numbers of metaxylem cells include numbers of mature and immature metaxylem cells. For determination of cell numbers and root diameters, three cell files from three individual plants were used. WT, wild-type. (This figure is available in colour at JXB online.)

Mentions: Sweetpotatoes cultured in vitro do not normally produce thick roots or storage roots on hormone-free MS medium, rather they produce only fibrous roots. Thus, to analyse the function of SRD1 in the formation of the storage root in an in vitro culture system, SRD1-overexpressing (ox) sweetpotato plants were generated under the control of the CaMV 35S promoter. Five independent SRD1-ox transgenic lines were obtained. Functional transformants were identified by PCR analysis of genomic DNA from the transgenic plants (Supplementary Fig. S4 at JXB online) and by detection of the increased levels of the SRD1 mRNA (Fig. 7A). SRD1 transcript accumulation in the fibrous roots of the SRD1-ox transgenic lines was moderately elevated in line 1 and strongly elevated in lines 2, 3, 4, and 5. Lines 1 and 3 were selected for further phenotypic analysis.


SRD1 is involved in the auxin-mediated initial thickening growth of storage root by enhancing proliferation of metaxylem and cambium cells in sweetpotato (Ipomoea batatas).

Noh SA, Lee HS, Huh EJ, Huh GH, Paek KH, Shin JS, Bae JM - J. Exp. Bot. (2010)

Characterization of SRD1-ox sweetpotato plants. (A) SRD1 transcript levels in SRD1-ox plants. Total RNA was isolated from fibrous root tissue of the sweetpotato plants cultured in vitro. Semi-quantitative RT-PCR analysis was conducted with SRD1-specific primers. Numbers 1–5 represent SRD1-ox sweetpotato lines 1–5. Sweetpotato β-tubulin was used as an equal loading internal control. WT, wild-type. (B) Morphology of the fibrous roots in SRD1-ox plants. Pictures were taken from the bottom of the culture plate for a better view of the root morphology. (C) Microscopic observation of the transverse section of fibrous root in the area marked with a box in B. The lower panel is an enlarged image of the upper panel. MPH, metaphloem; MX, metaxylem; PC, primary cambium; SC, secondary cambium; PXY, protoxylem. (D) Quantitative characterization of fibrous root development in SRD1-ox lines 1 and 3. Data were collected from the sweetpotato plants cultured in vitro at 14 d after planting and are the means±SD from three separate measurements of three individual plants. Root diameter and cell numbers were measured on transverse sections of fibrous roots. Root diameter was determined by measuring the largest diameter on the circle enclosed by epidermal cells. Numbers of metaxylem cells include numbers of mature and immature metaxylem cells. For determination of cell numbers and root diameters, three cell files from three individual plants were used. WT, wild-type. (This figure is available in colour at JXB online.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2837253&req=5

fig7: Characterization of SRD1-ox sweetpotato plants. (A) SRD1 transcript levels in SRD1-ox plants. Total RNA was isolated from fibrous root tissue of the sweetpotato plants cultured in vitro. Semi-quantitative RT-PCR analysis was conducted with SRD1-specific primers. Numbers 1–5 represent SRD1-ox sweetpotato lines 1–5. Sweetpotato β-tubulin was used as an equal loading internal control. WT, wild-type. (B) Morphology of the fibrous roots in SRD1-ox plants. Pictures were taken from the bottom of the culture plate for a better view of the root morphology. (C) Microscopic observation of the transverse section of fibrous root in the area marked with a box in B. The lower panel is an enlarged image of the upper panel. MPH, metaphloem; MX, metaxylem; PC, primary cambium; SC, secondary cambium; PXY, protoxylem. (D) Quantitative characterization of fibrous root development in SRD1-ox lines 1 and 3. Data were collected from the sweetpotato plants cultured in vitro at 14 d after planting and are the means±SD from three separate measurements of three individual plants. Root diameter and cell numbers were measured on transverse sections of fibrous roots. Root diameter was determined by measuring the largest diameter on the circle enclosed by epidermal cells. Numbers of metaxylem cells include numbers of mature and immature metaxylem cells. For determination of cell numbers and root diameters, three cell files from three individual plants were used. WT, wild-type. (This figure is available in colour at JXB online.)
Mentions: Sweetpotatoes cultured in vitro do not normally produce thick roots or storage roots on hormone-free MS medium, rather they produce only fibrous roots. Thus, to analyse the function of SRD1 in the formation of the storage root in an in vitro culture system, SRD1-overexpressing (ox) sweetpotato plants were generated under the control of the CaMV 35S promoter. Five independent SRD1-ox transgenic lines were obtained. Functional transformants were identified by PCR analysis of genomic DNA from the transgenic plants (Supplementary Fig. S4 at JXB online) and by detection of the increased levels of the SRD1 mRNA (Fig. 7A). SRD1 transcript accumulation in the fibrous roots of the SRD1-ox transgenic lines was moderately elevated in line 1 and strongly elevated in lines 2, 3, 4, and 5. Lines 1 and 3 were selected for further phenotypic analysis.

Bottom Line: SRD1 mRNA was mainly found in the actively dividing cells, including the vascular and cambium cells of the young storage root.During the early stage of storage root development, the endogenous IAA content and SRD1 transcript level increased concomitantly, suggesting an involvement of SRD1 during the early stage of the auxin-dependent development of the storage root.Taken together, these results demonstrate that SRD1 plays a role in the formation of storage roots by activating the proliferation of cambium and metaxylem cells to induce the initial thickening growth of storage roots in an auxin-dependent manner.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea.

ABSTRACT
A sweetpotato (Ipomoea batatas cv. 'Jinhongmi') MADS-box protein cDNA (SRD1) has been isolated from an early stage storage root cDNA library. The role of the SRD1 gene in the formation of the storage root in sweetpotato was investigated by an expression pattern analysis and characterization of SRD1-overexpressing (ox) transgenic sweetpotato plants. Transcripts of SRD1 were detected only in root tissues, with the fibrous root having low levels of the transcript and the young storage root showing relatively higher transcript levels. SRD1 mRNA was mainly found in the actively dividing cells, including the vascular and cambium cells of the young storage root. The transcript level of SRD1 in the fibrous roots increased in response to 1000 muM indole-3-acetic acid (IAA) applied exogenously. During the early stage of storage root development, the endogenous IAA content and SRD1 transcript level increased concomitantly, suggesting an involvement of SRD1 during the early stage of the auxin-dependent development of the storage root. SRD1-ox sweetpotato plants cultured in vitro produced thicker and shorter fibrous roots than wild-type plants. The metaxylem and cambium cells of the fibrous roots of SRD1-ox plants showed markedly enhanced proliferation, resulting in the fibrous roots of these plants showing an earlier thickening growth than those of wild-type plants. Taken together, these results demonstrate that SRD1 plays a role in the formation of storage roots by activating the proliferation of cambium and metaxylem cells to induce the initial thickening growth of storage roots in an auxin-dependent manner.

Show MeSH
Related in: MedlinePlus