title: 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.
abstract: Brassica juncea 3-hydroxy-3-methylglutaryl-CoA synthase (HMGS) is encoded by four isogenes (BjHMGS1-BjHMGS4). In vitro enzyme assays had indicated that the recombinant BjHMGS1 H188N mutant lacked substrate inhibition by acetoacetyl-CoA (AcAc-CoA) and showed 8-fold decreased enzyme activity. The S359A mutant demonstrated 10-fold higher activity, while the H188N/S359A double mutant displayed a 10-fold increased enzyme activity and lacked inhibition by AcAc-CoA. Here, wild-type and mutant BjHMGS1 were overexpressed in Arabidopsis to examine their effects in planta. The expression of selected genes in isoprenoid biosynthesis, isoprenoid content, seed germination and stress tolerance was analysed in HMGS overexpressors (OEs). Those mRNAs encoding enzymes 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), sterol methyltransferase 2 (SMT2), delta-24 sterol reductase (DWF1), C-22 sterol desaturase (CYP710A1) and brassinosteroid-6-oxidase 2 (BR6OX2) were up-regulated in HMGS-OEs. The total sterol content in leaves and seedlings of OE-wtBjHMGS1, OE-S359A and OE-H188N/S359A was significantly higher than OE-H188N. HMGS-OE seeds germinated earlier than wild-type and vector-transformed controls. HMGS-OEs further displayed reduced hydrogen peroxide (H(2) O(2) )-induced cell death and constitutive expression of salicylic acid (SA)-dependent pathogenesis-related genes (PR1, PR2 and PR5), resulting in an increased resistance to Botrytis cinerea, with OE-S359A showing the highest and OE-H188N the lowest tolerance. These results suggest that overexpression of HMGS up-regulates HMGR, SMT2, DWF1, CYP710A1 and BR6OX2, leading to enhanced sterol content and stress tolerance in Arabidopsis.
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Dinesh A
authors.initials: DA
authors.lastname: Nagegowda
authors.forename: Reetika
authors.initials: R
authors.lastname: Rawat
authors.forename: Pierrette
authors.initials: P
authors.lastname: Bouvier-Navé
authors.forename: Dianjing
authors.initials: D
authors.lastname: Guo
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Bach
authors.forename: Mee-Len
authors.initials: ML
authors.lastname: Chye
mesh_terms: D000214:Acyl Coenzyme A / Q000235:genetics / Q000378:metabolism*; D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000276:immunology / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects / Q000235:genetics; D020171:Botrytis / Q000187:drug effects / Q000502:physiology; D016923:Cell Death / Q000187:drug effects; D060467:Disease Resistance / Q000187:drug effects / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005822:Genetic Vectors / Q000235:genetics; D018525:Germination / Q000187:drug effects / Q000235:genetics; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009149:Mustard Plant / Q000187:drug effects / Q000201:enzymology*; D009154:Mutation / Q000235:genetics*; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000382:microbiology; D030821:Plants, Genetically Modified; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000382:microbiology; D013261:Sterols / Q000096:biosynthesis*; D013312:Stress, Physiological / Q000235:genetics*; D014170:Transformation, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics*
chemical_list: D000214:Acyl Coenzyme A; D029681:Arabidopsis Proteins; D013261:Sterols; C008047:3-hydroxy-3-methylglutaryl-coenzyme A; D006861:Hydrogen Peroxide