Potato steroidal glycoalkaloid levels and the expression of key isoprenoid metabolic genes.
The potato steroidal glycoalkaloids (SGA) are toxic secondary metabolites, and their total content in tubers should not exceed 20 mg/100 g fresh weight. The two major SGA in cultivated potato (Solanum tuberosum) are alpha-chaconine and alpha-solanine. SGA biosynthetic genes and the genetic factors that control their expression have not yet been determined. In the present study, potato genotypes exhibiting different levels of SGA content showed an association between high SGA levels in their leaves and tubers and high expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase 1 (hmg1) and squalene synthase 1 (pss1), genes of the mevalonic/isoprenoid pathway. Transcripts of other key enzymes of branches of the isoprenoid pathway, vetispiradiene/sesquiterpene synthase (pvs1) and sterol C24-methyltransferase type1 (smt1), were undetectable or exhibited stable expression regardless of SGA content, respectively, suggesting facilitated precursor flow to the SGA biosynthetic branch. The transcript ratio of solanidine glucosyltransferase (sgt2) to solanidine galactosyltransferase (sgt1) was correlated to the documented chaconine-to-solanine ratio in the tested genotypes. Significantly higher expression of hmg1, pss1, smt1, sgt1 and sgt2 was monitored in the tuber phelloderm than in the parenchyma of the tuber's flesh, targeting the former as the main SGA-producing tissue in the tuber, in agreement with the known high SGA content in the layers directly under the tuber skin.
Krits
Pinchas
P
Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.
Fogelman
Edna
E
Ginzberg
Idit
I
D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005838:Genotype; D008954:Models, Biological; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012991:Solanaceous Alkaloids / Q000378:metabolism*; D012992:Solanine / Q000031:analogs & derivatives / Q000378:metabolism; D011198:Solanum tuberosum / Q000235:genetics* / Q000378:metabolism*; D013729:Terpenes / Q000378:metabolism
D012991:Solanaceous Alkaloids; D013729:Terpenes; C514919:alpha-solanine; D012992:Solanine; C011860:alpha-chaconine
J Agric Food Chem. 2005 Jul 27;53(15):6162-9
16029012
Proc Natl Acad Sci U S A. 1994 Mar 15;91(6):2329-33
11607466
Eur J Biochem. 1995 Oct 15;233(2):506-13
7588795
Plant Physiol. 2003 Apr;131(4):1792-9
12692338
Plant Cell. 1991 Apr;3(4):397-405
1840919
Plant J. 1997 Feb;11(2):227-36
9076990
Plant Cell. 1992 Oct;4(10):1333-44
1283354
Plant Physiol. 1995 Dec;109(4):1337-1343
12228673
Theor Appl Genet. 2002 Nov;105(6-7):1010-1018
12582928
J Agric Food Chem. 2003 May 7;51(10):2964-73
12720378
Plant J. 2000 Aug;23(4):507-16
10972877
Phytochemistry. 2007 Feb;68(3):327-34
17157337
J Lipid Res. 1994 Jul;35(7):1133-40
7964176
Plant Physiol. 1987 Jun;84(2):404-8
16665452
J Chem Ecol. 1988 Oct;14(10):1941-50
24277104
Biosci Biotechnol Biochem. 2003 May;67(5):1007-17
12834277
Plant Cell Physiol. 1999 Sep;40(9):993-8
10588069
Eur J Biochem. 1992 Nov 1;209(3):923-31
1358611
Phytochemistry. 2006 Aug;67(15):1590-7
16298403
Plant Physiol. 1988 Dec;88(4):1291-6
16666457