Chloroplast localization of methylerythritol 4-phosphate pathway enzymes and regulation of mitochondrial genes in ispD and ispE albino mutants in Arabidopsis

Abstract

Plant isoprenoids are derived from two independent pathways, the cytosolic mevalonate pathway and the plastid methylerythritol 4-phosphate (MEP) pathway. We used green fluorescent fusion protein assays to demonstrate that the Arabidopsis MEP pathway enzymes are localized to the chloroplast. We have also characterized three Arabidopsis albino mutants, ispD-1, ispD-2 and ispE-1, which have T-DNA insertions in the IspD and IspE genes of the MEP pathway. Levels of photosynthetic pigments are almost undetectable in these albino mutants. Instead of thylakoids, the ispD and ispE mutant chloroplasts are filled with large vesicles. Impairments in chloroplast development and functions may signal changes in the expression of nuclear, chloroplast and mitochondrial genes. We used northern blot analysis to examine the expression of photosynthetic and respiratory genes in the ispD and ispE albino mutants. Steady-state mRNA levels of nucleus- and chloroplast-encoded photosynthetic genes are significantly decreased in the albino mutants. In contrast, transcript levels of nuclear and mitochondrial genes encoding subunits of the mitochondrial electron transport chain are increased or not affected in these mutants. Genomic Southern blot analysis revealed that the DNA amounts of mitochondrial genes are not enhanced in the ispD and ispE albino mutants. These results support the notion that the functional state of chloroplasts may affect the expression of nuclear and mitochondrial genes. The up-regulation of mitochondrial genes in the albino mutants is not caused by changes of mitochondrial DNA copy number in Arabidopsis.

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

“…Like the other albino mutants of the enzymes involved in MEP-related biosynthetic pathways, the dxr mutants exhibited an arrest in plastid development at early stages [20,22,30,[46][47][48]. This is consistent with the increased chlorophyll a/ b ratio observed in the pale inflorescence tissues, which are more sensitive to light due to the undeveloped plastids [49].…”

The amino-terminal conserved domain of 4-hydroxy-3-methylbut-2-enyl diphosphate reductase is critical for its function in oxygen-evolving photosynthetic organisms

“…However, it has been shown that the first 52 amino acids encompassing the predicted transit peptide of Arabidopsis HDR were sufficient to target the GFP reporter protein to the chloroplast. 14 In a recent report, we further demonstrated that the Arabidopsis HDRDNCD-GFP fusion protein was localized to the chloroplast. 21 Thus, the NCD is not required for targeting the Arabidopsis HDR enzyme to the chloroplast.…”

“…[14][15][16][17][18][19][20] The 4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) reductase, commonly known as HDR, isoprenoid synthesis H (IspH), or lysis-tolerant B (LytB), catalyzes the last step of the MEP pathway that converts HMBPP into a 5:1 mixture of IPP and DMAPP in Escherichia coli. 12,13 In Arabidopsis thaliana, the hdr-1 knockout mutant is albino lethal and the HDR transgene-induced genesilencing lines are albino, pale green, or variegated.…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…The chamomile sesquiterpenes are an adequate example showing clear metabolic crosstalk between the two pathways in which both provide IPP precursors for the production of certain terpenoids that consist of 2 five-carbon isoprene units, which are derivatives of the MEP pathway, while the third unit is formed by both pathways (Towler and Weathers 2007). In the plastids, the MEP pathway (Hsieh et al 2008) results in the formation of IPP and DMAPP from G3P and pyruvate. However, the classical independent MVA pathway (Vranová et al 2013) is disseminated in the cytosol, peroxisomes and endoplasmic reticulum (Pulido et al 2012).…”