Antisense expression of hmg1 from Arabidopsis thaliana encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase, reduces isoprenoid production in transgenic tobacco plants

With the aim of studying the production of chloroplast isoprenoid derivatives, chimeric gene constructs comprising partial and full-length forms of the Arabidopsis thaliana hmg 1 gene, encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), in sense and antisense forms were fused to a chloroplast transit peptide (CTP) sequence from a pea ribulose bisphosphate carboxylase/oxygenase (Rubisco) small subunit gene. These plasmids were placed downstream from the constitutive CaMV 35S promoter and introduced into tobacco (Nicotiana tabacum cv. Xanthi) by Agrobacterium-mediated transformation. Southern and northern blot analysis confirmed the transformation and transcription of the respective constructs within transgenic tobacco plants. In addition total and chloroplast specific HMGR enzyme activities, and the levels of chlorophyll, carotenoids and total sterols were analyzed. Results of these analyses suggest that neither partial nor full-length sense constructs had any effect on chloroplast isoprenoid production. However, the corresponding antisense constructs decreased general isoprenoid levels. The significance of these results is discussed.