RESUMO
Steroidal glycoalkaloids (SGAs) such as α-solanine found in solanaceous food plants--as, for example, potato--are antinutritional factors for humans. Comparative coexpression analysis between tomato and potato coupled with chemical profiling revealed an array of 10 genes that partake in SGA biosynthesis. We discovered that six of them exist as a cluster on chromosome 7, whereas an additional two are adjacent in a duplicated genomic region on chromosome 12. Following systematic functional analysis, we suggest a revised SGA biosynthetic pathway starting from cholesterol up to the tetrasaccharide moiety linked to the tomato SGA aglycone. Silencing GLYCOALKALOID METABOLISM 4 prevented accumulation of SGAs in potato tubers and tomato fruit. This may provide a means for removal of unsafe, antinutritional substances present in these widely used food crops.
Assuntos
Produtos Agrícolas/genética , Família Multigênica , Valor Nutritivo/genética , Alcaloides de Solanáceas/biossíntese , Alcaloides de Solanáceas/genética , Solanum lycopersicum/genética , Solanum tuberosum/genética , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Genes de Plantas , Alcaloides de Solanáceas/toxicidadeRESUMO
Pigeonpea (Cajanus cajan L) seeds were analysed quantitatively for amylase inhibitor (AI) activity and qualitatively, by an in-gel-detection method on polyacrylamide gels. At least four AI isoforms were identified in pigeonpea seeds. The AIs inhibit human salivary and bovine pancreatic amylase but fail to inhibit bacterial, fungal and endogenous amylase. Pigeonpea AIs were found to be active over a pH range of 4.5 to 9.5 and were heat labile. The isoelectric point of a major inhibitor is 6.2 AIs were tolerant to proteolysis by trypsin, chymotrypsin, bromelain and endogenous pigeonpea proteases. Pigeonpea AIs were synthesized during late seed development and also degraded during late germination. Addition of AIs or protease inhibitors (PIs) alone to a diet of Helicoverpa armigera larvae did not increase mortality. However, the larvae reared on a diet containing AIs and PIs in combination, showed increased mortality and adverse effects on larval growth and development. In vitro inhibition of Helicoverpa gut amylase revealed that only 22% activity is sensitive to inhibitors. Further investigations on interactions of pigeonpea AIs and PIs with Helicoverpa gut enzymes is necessary to develop strategies to strengthen defense mechanisms in pigeonpea against H. armigera.