Expression and Molecular Analysis of the ArabidopsisDXR Gene Encoding 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase, the First Committed Enzyme of the 2-C-Methyl-d-Erythritol 4-Phosphate Pathway

Abstract

1-Deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) catalyzes the first committed step of the 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis. In Arabidopsis, DXR is encoded by a single-copy gene. We have cloned a full-length cDNA corresponding to this gene. A comparative analysis of all plant DXR sequences known to date predicted an N-terminal transit peptide for plastids, with a conserved cleavage site, and a conserved proline-rich region at the N terminus of the mature protein, which is not present in the prokaryotic DXR homologs. We demonstrate that Arabidopsis DXR is targeted to plastids and localizes into chloroplasts of leaf cells. The presence of the proline-rich region in the mature Arabidopsis DXR was confirmed by detection with a specific antibody. A proof of the enzymatic function of this protein was obtained by complementation of anEscherichia coli mutant defective in DXR activity. The expression pattern of β-glucuronidase, driven by theDXR promoter in Arabidopsis transgenic plants, together with the tissue distribution of DXR transcript and protein, revealed developmental and environmental regulation of theDXR gene. The expression pattern of theDXR gene parallels that of the Arabidopsis 1-deoxy-d-xylulose 5-phosphate synthase gene, but the former is slightly more restricted. These genes are expressed in most organs of the plant including roots, with higher levels in seedlings and inflorescences. The block of the 2-C-methyl-d-erythritol 4-phosphate pathway in Arabidopsis seedlings with fosmidomycin led to a rapid accumulation of DXR protein, whereas the 1-deoxy-d-xylulose 5-phosphate synthase protein level was not altered. Our results are consistent with the participation of the Arabidopsis DXR gene in the control of the 2-C-methyl-d-erythritol 4-phosphate pathway.

Disruption of the 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) gene results in albino, dwarf and defects in trichome initiation and stomata closure in Arabidopsis

“…There are at least two possibilities. One is posttranscriptional regulation of DXR, such as translational modulation [19,53]. In Arabidopsis, HMGR, a critical enzyme involved in the MVA pathway, has even more complicated regulation mechanisms [26,[54][55][56][57].…”

“…In this pathway, DXS has been identified to catalyze the first step, the key step of the MEP pathway, in Arabidopsis [22,47,58]. DXS was also found to share a similar expression pattern with DXR, and both DXS and DXR null mutants displayed an [7,19,22,47]. Many studies on comparisons between DXR and DXS have also been carried out [7,19].…”

“…DXS was also found to share a similar expression pattern with DXR, and both DXS and DXR null mutants displayed an [7,19,22,47]. Many studies on comparisons between DXR and DXS have also been carried out [7,19]. Possibly, for those non-determinant enzymes such as DXR, their expression levels are normally more than needed, and metabolic changes will only be triggered after the changes of the enzymes reach a certain threshold.…”

“…Previous studies have shown that DXR played a critical role in directing the intermediate flux into IPP and DMAPP biosynthetic pathways [19,20]. Overexpression of DXR resulted in an increase in biosynthesis of essential oils in mint and an increase in photosynthetic pigment levels in Arabidopsis [20,21].…”

“…The transcript pattern of DXR covers almost all plant organs, with the highest level in inflorescence tissue [19,22]. Blocking of DXR activity using the specific inhibitor fosmidomycin (FSM) led to the accumulation of DXR protein, the bleach phenotype, and the failure of seedling establishment [19,20,[23][24][25][26]. An insertion mutant of DXR was found to be an albino, and down-regulation of DXR transcript level resulted in abnormal chloroplast development [20,27].…”