The 3-Hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS) codes for
isoprenoids including phytosterols, which can lower blood cholesterol
levels. In a previous study, overexpressing the mustard (Brassica juncea)
BjHMGS1 genein Arabidopsis and tobacco upregulated genes in the sterol
biosynthesis and increased its sterol content. The team of Pan Liao of the
University of Hong Kong aimed to overexpress the wildtype (HGMS) and mutant
(S359A) BjHMGS1 genes in tomato (Solanum lycopersicum).
Overexpression of either gene caused an accumulation of MVA-derived squalene
and phytosterols, as well as vitamin E and carotenoids, in tomato. In tomato
with the HMGS-overexpressing seedlings, genes associated with the
biosyntheses of universal precursors of several compounds, including
phytosterols, brassinosteroids, carotenoids, and vitamin E were upregulated.
However, the S359A-overexpressing tomato fruits had greater squalene and
phytosterol contents over the HMGS-overexpressing plants.
This study demonstrates that manipulation of the BjHMGS1 gene is a potential
strategy to simultaneously elevate health-promoting squalene, phytosterols,
á-tocopherol, and carotenoids in tomato.