Expression of this gene in yeast rer2 complements its thermosensitive phenotype ( Cunillera et al., 2000). Through comparison of cis-prenyltransferase sequences with plant genomic sequences, a homologous gene ( AT2G23410) was cloned from Arabidopsis thaliana ( Cunillera et al., 2000 Oh et al., 2000). By contrast, the str1 mutant does not have noticeable phenotypes ( Sato et al., 2001). rer2 shows many phenotypes, including temperature and hygromycin sensitivity, slow growth, defects in N- and O-glycosylation, and abnormal accumulation of ER and Golgi membranes ( Sato et al., 1999). The multicopy suppressor of rer2, STR1, encodes a protein similar to RER2, but with different physiological roles during cell growth ( Sato et al., 2001).
The first eukaryotic cis-prenyltransferase–encoding gene, RER2, which is responsible for dolichol synthesis, was cloned from the yeast mutant rer2 ( Sato et al., 1999). Dolichyl phosphate serves as a glycosyl carrier lipid in the biosyntheses of protein C- and O-mannosylation, in glycosylphosphatidylinositol anchors, and is one of the rate-limiting factors in N-linked protein glycosylation in yeast and mammalian cells ( Burda and Aebi, 1999 Jones et al., 2005).
#Unfolder in samsung galaxy s7 series#
Polyprenyl diphosphate is further converted to dolichol and dolichyl phosphate by a series of reactions ( Grabinska and Palamarczyk, 2002). The number of IPPs added is species-dependent. The formation of longer chain polyprenyl diphosphate is catalyzed by enzymes called cis-prenyltransferases, which sequentially add isopentenyl diphosphates (IPPs) onto FPP ( Grabinska and Palamarczyk, 2002). This biosynthesis is initiated by the formation of farnesyl diphosphate (FPP), primarily through the mevalonate pathway ( Chojnacki and Dallner, 1988 Swiezewskaa and Danikiewiczb, 2005). The biosynthesis of dolichols takes place mainly in the endoplasmic reticulum (ER) and to a lesser extent in peroxisomes ( Chojnacki and Dallner, 1988).
#Unfolder in samsung galaxy s7 free#
Dolichols exist as free alcohols or products derived by phosphorylation, esterification, or glycosylation ( Chojnacki and Dallner, 1988 Swiezewskaa and Danikiewiczb, 2005). They are localized within the two halves of the phospholipid bilayer, with high contents in the plasma membranes, peroxisomes, Golgi vesicles, and lysosomes. In animals, dolichols are broadly distributed in different cells. INTRODUCTIONĭolichols are long-chain unsaturated polyisoprenoids present in all eukaryotic cells they consist of 15 to 23 isoprenic units depending on the species ( Chojnacki and Dallner, 1988 Swiezewskaa and Danikiewiczb, 2005). Genetic, molecular, and physiological analyses of the glycosylation defective lew1 mutant show that drought stress signaling converges with endoplasmic reticulum (ER) signaling to regulate ER/UPR (unfolded protein response) and osmotic stress responses. This work describes the isolation and biochemical characterization of the leaf wilting1 (lew1) gene that is responsible for the biosynthesis of dolichols in Arabidopsis. Our data suggest that LEW1 catalyzes dolichol biosynthesis and that dolichol is important for plant responses to endoplasmic reticulum stress, drought, and dark-induced senescence in Arabidopsis. The lew1 mutant was more sensitive to dark treatment, but this dark sensitivity was suppressed by drought treatment. Interestingly, drought stress in the lew1 mutant induced higher expression of the unfolded protein response pathway genes BINDING PROTEIN and BASIC DOMAIN/LEUCINE ZIPPER60 as well as earlier expression of the stress-responsive genes RD29A and COR47. The mutation also impaired plasma membrane integrity, causing electrolyte leakage, lower turgor, reduced stomatal conductance, and increased drought resistance. The lew1 mutation reduced the total plant content of main dolichols by ∼85% and caused protein glycosylation defects. LEW1 encoded a cis-prenyltransferase, which when expressed in Escherichia coli catalyzed the formation of dolichol with a chain length around C 80 in an in vitro assay.
We isolated an Arabidopsis thaliana mutant, lew1 (for leaf wilting1), that showed a leaf-wilting phenotype under normal growth conditions. The biological functions of dolichols in plants are largely unknown. Dolichols are long-chain unsaturated polyisoprenoids with multiple cellular functions, such as serving as lipid carriers of sugars used for protein glycosylation, which affects protein trafficking in the endoplasmic reticulum.
0 kommentar(er)
