Potato steroidal glycoalkaloid levels and the expression of key isoprenoid metabolic genes

Abstract

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.

Hybrids and allied species as potential rootstocks for eggplant: Effect of grafting on vigour, yield and overall fruit quality traits

“…Jones and Fenwick, (2006) and Krits et al (2007) suggested that the level of total glycoalkaloids in potato tubers should not exceed 200 mg/kg of fw (or 200 mg/100 g of dw). Although ANOVA showed no significant effect of the rootstock on glycoalkaloids concentration, our results revealed a certain effect of rootstocks on glycoalkaloids content.…”

GLYCOALKALOID METABOLISM1 Is Required for Steroidal Alkaloid Glycosylation and Prevention of Phytotoxicity in Tomato

“…In most cultivated potato species, derivatives of 3-O-glucosylsolanidine are more abundant than those of 3-O-galactosylsolanidine (Friedman et al, 2003). Interestingly, several genotypes of Solanum chacoense exhibit higher relative levels of SGT1 (galactosyltransferase) than of SGT2 (glucosyltransferase), suggesting an opposite SA 3-O-glycosylation ratio (galactosylation/glucosylation) (Krits et al, 2007). Enzyme activity assays performed herein, together with previously published data (Zimowski, 1998), support a different mechanism in tomato for regulating the 3-O-glycosylated SA ratio.…”

Cloning and expression analysis of squalene synthase, a key enzyme involved in antifungal steroidal glycoalkaloids biosynthesis from Solanum nigrum

“…SGAs accumulation appears to be regulated at different steps in the biosynthetic pathway in response to environmental stress and development. High transcript levels of potato HMGR and squalene synthase encoding genes were shown to be associated with high SGA levels (8), implying that the regulation of SGA biosynthesis involves the committed step of the mevalonate pathway as well as later steps of SGA formation. It indicated that along with HMGR, Original Article DOI: 10.5582/ddt.2012.v6.…”