Expression of Brassica juncea 3‐hydroxy‐3‐methylglutaryl CoA synthase is developmentally regulated and stress‐responsive

Abstract

Summary 3-Hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS) is an enzyme in mevalonate biosynthesis. In plants, investigations have focused on HMG CoA reductase (HMGR) and less is known of the preceding enzyme, HMGS. To understand the regulation of HMGS, we have isolated a Brassica juncea cDNA encoding HMGS, BjHMGS1, for use as a hybridization probe in Northern blot analyses. BjHMGS is expressed in all plant organs and shows developmental regulation in¯ower, seed and seedling, with highest expression in early development. In seedlings, expression is highest in young hypocotyls and is induced during the greening of etiolated cotyledons. BjHMGS is down-regulated by abscisic acid, osmotic stress and dehydration, the effects of which arrested seedling growth. Thus BjHMGS expression shows correlation with rapid cell division and growth, like HMGR. This is not unexpected, as mevalonate is the precursor to many essential isoprenoid compounds, including sterols for membrane biogenesis. Wounding, methyl jasmonate or salicylic acid induce BjHMGS expression, suggesting that, like HMGR, HMGS is involved in defence. As in animals, coordinated regulation of HMGS with HMGR occurred in B. juncea upon germination and in response to salicylic acid. HMGS assays con®rmed that Escherichia coliexpressed recombinant BjHMGS1 shows HMGS activity that is inhibited by F244, a speci®c inhibitor of HMGS. Southern blot analysis revealed gene families encoding HMGS in Brassica species and a summation of homologous genes in the fusion amphidiploid genome of B. juncea, a bi-parental species derived from diploids B. nigra and B. campestris.

Overexpression of Brassica juncea wild‐type and mutant HMG‐CoA synthase 1 in Arabidopsis up‐regulates genes in sterol biosynthesis and enhances sterol production and stress tolerance

“…, 2000). BjHMGS was down‐regulated by ABA, osmotic stress and dehydration and up‐regulated by salicylic acid (SA), methyl jasmonate (MeJA) and wounding (Alex et al. , 2000).…”

“…The aim of this study was to investigate the effects of overexpression of wild‐type (wt) and mutant (H188N, S359A and H188N/S359A) BjHMGS1 in Arabidopsis thaliana Col‐0. HMGS overexpression in Arabidopsis HMGS‐OEs not only elevated the expression of HMGR , given that both are co‐ordinately regulated in B. juncea (Alex et al. , 2000), but SMT2, DWF1 , CYP710A1 and BR6OX2 , further down in the MVA pathway related to sterol biosynthesis, were also induced.…”

Transgenic Tobacco Overexpressing Brassica juncea HMG-CoA Synthase 1 Shows Increased Plant Growth, Pod Size and Seed Yield

“…HMGS has been shown to play a crucial role in floral development [4], [34], [35], [37]. In Arabidopsis , higher AtHMGS expression had been observed in flowers than seedlings or leaves from RT-PCR analysis [4].…”

“…Using mutants in HMGS , AtHMGS was demonstrated essential for pollen fertility and proper development of tapetum-specific organelles in Arabidopsis [35]. In B. juncea , northern blot analysis had previously revealed that BjHMGS1 mRNA was highly expressed in flowers and seedling hypocotyls [34] and in situ hybridization analysis had shown that HMGS mRNA was predominantly localized in the stigmata and ovules of flower buds and in the piths of seedling hypocotyls [37]. BjHMGS1 and BjHMGS2 , but not BjHMGS3 and BjHMGS4 expression was detected in the floral buds as examined by RT-PCR analysis [37].…”

“…Besides 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), HMGS is a key enzyme in cholesterol biosynthesis in mammals and cytoplasmic isoprenoid biosynthesis in plants [3], [4], [32]–[36]. Four genes designated BjHMGS1 to BjHMGS4 encode HMGS in Brassica juncea [34] and investigations revealed that BjHMGS1 is cytosolic. The expression of recombinant BjHMGS1 led to the elucidation of its kinetic and physiological properties [37], [38] and of its crystal structure [39].…”