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. 2003 Apr;131(4):1792-9.
doi: 10.1104/pp.102.018788.

Reduction of cholesterol and glycoalkaloid levels in transgenic potato plants by overexpression of a type 1 sterol methyltransferase cDNA

Lisa Arnqvist  1 , Paresh C Dutta, Lisbeth Jonsson, Folke Sitbon
Affiliations

Reduction of cholesterol and glycoalkaloid levels in transgenic potato plants by overexpression of a type 1 sterol methyltransferase cDNA

Lisa Arnqvist et al. Plant Physiol. 2003 Apr.

Abstract

Transgenic potato (Solanum tuberosum cv Désirée) plants overexpressing a soybean (Glycine max) type 1 sterol methyltransferase (GmSMT1) cDNA were generated and used to study sterol biosynthesis in relation to the production of toxic glycoalkaloids. Transgenic plants displayed an increased total sterol level in both leaves and tubers, mainly due to increased levels of the 24-ethyl sterols isofucosterol and sitosterol. The higher total sterol level was due to increases in both free and esterified sterols. However, the level of free cholesterol, a nonalkylated sterol, was decreased. Associated with this was a decreased glycoalkaloid level in leaves and tubers, down to 41% and 63% of wild-type levels, respectively. The results show that glycoalkaloid biosynthesis can be down-regulated in transgenic potato plants by reducing the content of free nonalkylated sterols, and they support the view of cholesterol as a precursor in glycoalkaloid biosynthesis.

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Figures

Figure 1
Figure 1
Schematic presentation of proposed sterol and glycoalkaloid biosynthesis pathways in potato plants (adapted from Bergenstråhle et al. [1996] and Choe et al. [1999]). Dashed arrows indicate more than one enzymatic step. The methylation steps catalyzed by SMT1 and SMT2 are indicated.
Figure 2
Figure 2
Northern-blot analysis of GmSMT1 expression in leaves (A) and tubers (B) from wild-type and transgenic GmSMT1 potato plants. Total RNA in young leaves and tubers was extracted from plants grown in a climate chamber or a greenhouse, respectively. Twenty micrograms of RNA was separated on formaldehyde gels, blotted onto a nylon filter, and hybridized with labeled DNA probes for GmSMT1 and rRNA (loading control). B, In tubers, a weak signal was detected for the clones 126 and 231 after prolonged exposure of the film.
Figure 3
Figure 3
Sterol composition in leaves (A) and tubers (B) from wild-type and transgenic GmSMT1 potato plants. Sterols were extracted from leaves and tubers and analyzed in duplicate by gas chromatography confirmed with mass spectrometry. White staples, Wild-type plants (A, n = 8 plants; B, n = 3); black staples, transgenic plants (n = 3), from left to right clones 118, 217, 232, and 286. Mean values + sd. ND, Not detected.
Figure 4
Figure 4
Free and esterified sterols in leaves (A and B) and tubers (C and D) from wild-type and transgenic GmSMT1 potato plants. Sterols were extracted from leaves and tubers and analyzed in duplicate by gas chromatography confirmed with mass spectrometry. White staples, Wild type; black staples, transgenic clones, from left to right clones 118 and 217. Mean values + sd, n = 3 plants. ND, Not detected.
Figure 5
Figure 5
TGA levels in leaves (A) and tubers (B) from wild-type and transgenic GmSMT1 potato plants. Levels of α-chaconine (lower part of staple) and α-solanine (upper part of staple) were analyzed in duplicate by HPLC. The average difference from the mean in duplicate analyses was 1.9%. White staples, Wild-type plants (A, n = 3; B, n = 6 plants); black staples, transgenic plants (A, n = 1; B, n = 2, for clones 118 and 217, n = 3). Mean values + sd. sd was calculated from the sum of α-chaconine and α-solanine in the samples analyzed. The analysis of tubers was carried out in two independent experiments, giving similar results.
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References

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