Enhancing plant growth, seed yield and sterol content through manipulation of 3-hydroxy-3-methylglutaryl coenzyme A synthase

Abstract

Due to the importance of plant isoprenoids, several attempts had been made to achieve some overproduction. Rate-limiting reactions in the MVA pathway like that catalyzed by HMG-CoA reductase were initially considered, also of enzymes downstream. In previous work we had studied the role and kinetics of the second enzyme in the MVA pathway, HMG-CoA synthase in Brassica juncea (BjHMGS1), including the effect of targeted mutation of several amino acid residues and could generate an enzyme with higher catalytic efficiency in vitro. WT BjHMGS1 and BjHMGS1S393A were transformed into Arabidopsis, resulting in positive effects such as an increased resistance to stress. This has been extended to tobacco over-expressing wild-type (OE-wtBjHMGS1) and mutant BjHMGSS359A (OE-S359A), which resulted in higher accumulation of total phytosterols than in the vector-transformed control, with OE-S359A showing some higher sterol increase than OE-wtBjHMGS1. The over-expression of HMGS up-regulated several downstream genes in the isoprenoid pathway and was found to accelerate and promote plant growth, leading to a higher yield of seeds, which both are interesting agricultural traits. The role of HMGSfor plant growth is supported by the existence of natural inhibitors like F-244, efficiently retarding growth of B juncea seedlings and tobacco BY 2 cells.