ABSTRACT
We isolated two full-length cDNA clones encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) from potato (Solanum tuberosum) L. tubers. The clones, designated hmg2.2 and hmg3.3, are members of previously described gene subfamilies. In addition to being induced by arachidonic acid in tubers, hmg2.2 transcript accumulates developmentally in young flowers, and in mature sepals and ovaries, whereas transcript for hmg3.3 accumulates in mature petals and anthers. Our data suggest that members of specific HMGR-encoding gene subfamilies might be involved in both defense responses and flower development. Accumulation of different HMGR transcripts could provide some control of isoprenoid biosynthesis by producing isoforms specific for classes of end-products produced in particular tissues.
Subject(s)
Gene Expression Regulation, Plant , Hydroxymethylglutaryl CoA Reductases/genetics , Multigene Family , Plant Proteins/genetics , Solanum tuberosum/enzymology , Solanum tuberosum/genetics , Transcription, Genetic , Amino Acid Sequence , Arachidonic Acid/pharmacology , Cloning, Molecular , DNA, Complementary/biosynthesis , Gene Expression Regulation, Developmental , Hydroxymethylglutaryl CoA Reductases/biosynthesis , Hydroxymethylglutaryl CoA Reductases/isolation & purification , Molecular Sequence Data , Plant Proteins/biosynthesis , Plant Proteins/isolation & purification , Plant Stems/enzymology , Plant Stems/geneticsABSTRACT
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) catalyzes a key step in isoprenoid metabolism leading to a range of compounds that are important for the growth, development and health of the plant. We have isolated 7 classes of genomic clones encoding HMGR from a potato genomic library. Comparison of nucleic acid sequences reveals a high degree of identity between all seven classes of clones and the potato hmg 1 gene described by Choi et al. (Plant Cell 4: 1333, 1992), indicating that all are members of the same subfamily in potato. A representative member (hmg 1.2) of the most abundant class of genomic clones was selected for further characterization. Transgenic tobacco and potato containing the beta-glucuronidase (GUS) reporter gene under the control of the hmg 1.2 promoter expressed GUS activity constitutively at a low level in many plant tissues. High levels of GUS activity were observed only in the pollen. GUS assays of isolated pollen, correlations of GUS activity with the HMGR activity of anthers, hmg 1.2 promoter deletion studies, and segregation analysis of the expression of hmg 1.2::GUS among the R2 pollen of R1 progeny plants demonstrated that the hmg 1.2 promoter controls pollen expression.
Subject(s)
Genes, Plant/genetics , Hydroxymethylglutaryl CoA Reductases/genetics , Multigene Family/genetics , Solanum tuberosum/genetics , Amino Acid Sequence , Base Sequence , Blotting, Northern , Blotting, Southern , DNA, Complementary/genetics , Genes, Reporter , Genomic Library , Glucuronidase/genetics , Hydroxymethylglutaryl CoA Reductases/classification , Molecular Sequence Data , Plants, Genetically Modified , Plants, Toxic , Pollen/genetics , Promoter Regions, Genetic/genetics , RNA, Messenger/genetics , Sequence Analysis, DNA , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Tissue Distribution , Nicotiana/genetics , Transformation, GeneticABSTRACT
This brief review summarizes the current literature on the regulation of HMG-CoA reductase (HMGR) in plants. The mevalonate pathway, which starts with the synthesis of mevalonate by HMGR, has more branch pathways in plants than in most other organisms, leading to a tremendous variety of isoprenoid products. Evidence suggests that HMGR is an important control point for the synthesis of many of these plant isoprenoids, including some that are vital for primary metabolism and pest resistance. Plant HMGR activity responds in vivo to a variety of developmental and environmental signals, such as cell division, light, and infection. Plants regulate HMGR activity at the level of mRNA by differential induction of HMGR gene family members, and posttranslationally by enzyme modification. Calcium, calmodulin, and proteolytic degradation may also have a role in regulation of plant HMGR.
Subject(s)
Hydroxymethylglutaryl CoA Reductases/metabolism , Plants/enzymology , Calcium/physiology , Cell Compartmentation/physiology , Peptide Hydrolases/metabolism , Phosphorylation , Signal Transduction/physiology , Transcription, GeneticABSTRACT
The importance of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) in the regulation of sesquiterpenoid phytoalexin accumulation in potato (Solanum tuberosum L. cv Kennebec) was examined. Wounding of potato tubers produced a large temporary increase in HMG-CoA reductase activity of the microsomal and organelle fractions. Treatment of wounded tuber tissue with the sesquiterpenoid phytoalexin elicitor arachidonic acid further increased and prolonged the HMG-CoA reductase activity in the microsomal but not the organelle fraction. Incubation of elicitor-treated tuber tissue in white light reduced organelle and microsomal HMG-CoA reductase activity to 50% and 10%, respectively, of the activity of tissues held in darkness. Constant light also reduced overall phytoalexin accumulation 58% by greatly reducing levels of lubimin. Rishitin accumulation was not significantly altered by light. Application of nanomolar amounts of mevinolin, a highly specific inhibitor of HMG-CoA reductase, to elicitor-treated tuber tissue produced a large decline in lubimin accumulation and did not markedly alter rishitin accumulation. These results indicate that HMG-CoA reductase has a role in the complex regulation of sesquiterpenoid phytoalexin accumulation in potato.
