Expression of the Arabidopsis HMG2 Gene, Encoding 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase, Is Restricted to Meristematic and Floral Tissues

Abstract

The synthesis of mevalonate, which is considered the first rate-limiting step in isoprenoid biosynthesis, is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC 1.1.1.34). In Arabidopsis, HMGR is encoded by two differentially expressed genes (HMG1 and HMG2). The transcriptional activity of the HMG2 gene was studied after fusing different regions of its 5' flanking region to the beta-glucuronidase (GUS) reporter gene and transforming the resulting constructs into tobacco plants. The spatial and temporal expression directed by the HMG2 promoter in the transgenic plants is consistent with the expression pattern previously established by RNA analysis using an HMG2-specific probe. HMG2 expression is restricted to meristematic (root tip and shoot apex) and floral (secretory zone of the stigma, mature pollen grains, gynoecium vascular tissue, and fertilized ovules) tissues. Deletion analysis of the HMG2 5' flanking region was conducted in transgenic plants and transfected protoplasts. The region containing nucleotides -857 to +64 of the HMG2 gene was sufficient to confer high levels of expression in both floral and meristematic tissues, although deletion to nucleotide -503 resulted in almost complete loss of expression. Sequences contained within the 5' transcribed, untranslated region are also important for gene expression. The biological significance of the restricted pattern of expression of HMG2 is also discussed.

Distinct Light-Mediated Pathways Regulate the Biosynthesis and Exchange of Isoprenoid Precursors during Arabidopsis Seedling Development

“…We first determined whether higher levels of HMGR-encoding mRNAs were present in rim1 (Figure 4). Transcript levels of HMG1 and HMG2 , the two Arabidopsis genes that encode HMGR (Enjuto et al, 1994(Enjuto et al, , 1995Learned and Connolly, 1997), were increased significantly in rim1 seedlings compared with the wild type ( Figures 4A and 4B), resulting in 45% higher HMGR activity ( Figure 4C). To determine whether this increase in enzyme activity could explain the MEV resistance of rim1 , we quantified this phenotype in transgenic H1S and H1cd/3 plants showing different HMGR activity levels (González, 2002).…”

“…When seeds germinate in the dark, a very early induction of HMGRencoding genes leads to an active MVA pathway in etiolated seedlings (Enjuto et al, 1994(Enjuto et al, , 1995Learned and Connolly, 1997). Because etiolated growth involves high cell elongation rates, it can be expected that MVA-derived isoprenoids, such as sterols and brassinosteroids, are required at high levels.…”

Salt regulation of transcript levels for the c subunit of a leaf vacuolar H+‐ATPase in the halophyte Mesembryanthemum crystallinum

“…The 5'-untranslated sequence also contained a CT-rich region located from positions 47 to 77. Such elements may be involved in the control of gene expression (Enjuto et al, 1995), and are also present in the 5'-untranslated region of the salt-inducible Ppcl gene encoding the CAM-specific form of PEPC in M. crystallinum (Cushman and Bohnert, 1996). An extensive 3' end of 376 nt did not include the poly(A) + tail, but contained two putative polyadenylation signal consensus sequences (AATAAA: Rothnie etal., 1994), as well as two sequence motifs (TTGTA) characteristic of far-upstream elements involved in the selection of polyadenylation sites in plants (Hunt, 1994).…”

Proliferation and Morphogenesis of the Endoplasmic Reticulum Driven by the Membrane Domain of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in Plant Cells

“…Isozymes HMGR1S and HMGR1L are identical in sequence, but HMGR1L has an N-terminal extension of 50-amino acid residues (1L extra region). HMGR1S transcript is expressed in the whole plant, whereas those encoding HMGR2 or HMGR1L are detected at a much lower level and only in meristems, seedlings, roots, and inflorescences (Enjuto et al, 1994(Enjuto et al, , 1995Lumbreras et al, 1995). Chimeras formed by the membrane domain of plant HMGR fused to GFP localize in the ER network but accumulate in highly fluorescent cytosolic bodies (Leivar et al, 2005;Merret et al, 2007).…”