Carotenoids are pigments required for photosynthesis, photoprotection and the production of carotenoid- derived hormones such as ABA and strigolactones. The carotenoid biosynthetic pathway bifurcates after lycopene to...Carotenoids are pigments required for photosynthesis, photoprotection and the production of carotenoid- derived hormones such as ABA and strigolactones. The carotenoid biosynthetic pathway bifurcates after lycopene to produce epsilon- and beta-carotenoids and this branch is critical for determining carotenoid composition. Here, we show how the branch point can be regulated by the chromatin-modifying histone methyltransferase, Set Domain Group 8 （SDG8） targeting the carotenoid isomerase （CRTISO）. SDG8 is required to maintain permissive expression of CRTISO during seedling development, in leaves, shoot apex, and some floral organs. The CRTISO and SDG8 promoters show overlapping tissue-specific patterns of reporter gene activity. Interestingly, CRTISO showed atypical reporter gene expression in terms of greater variability between different lines compared to the Cauliflower Mosaic Virus 35S promoter （CaMV35s） and ~LCY promoters, potentially due to chromosomal position effects. Regulation of the CRTISO promoter was dependent in part upon the presence or absence of SDG8. Knockouts of SDG8 （carotenoid and chloroplast regulation （ccrl）） and CRTISO （ccr2） result in altered carotenoid composition and this could be restored in ccr2 using the CaMV35s or CRTISO promoters. In contrast, varying degrees of GUS expression and carotenoid complementation by CRTISO overexpression using CaMV35S or CRTISO promoters in the ccrl background demonstrated that both the CRTISO promoter and open reading frame are necessary for SDG8-mediated expression of CRTISO.展开更多
The biosynthesis of isoprenoids in plant cells occurs from precursors produced in the cytosol by the mevalonate （MVA） pathway and in the plastid by the methylerythritol 4-phosphate （MEP） pathway, but little is kno...The biosynthesis of isoprenoids in plant cells occurs from precursors produced in the cytosol by the mevalonate （MVA） pathway and in the plastid by the methylerythritol 4-phosphate （MEP） pathway, but little is known about the mechanisms coordinating both pathways. Evidence of the importance of sugar signaling for such coordination in Arabi- dopsis thaliana is provided here by the characterization of a mutant showing an increased accumulation of MEP-derived isoprenoid products （chlorophylls and carotenoids） without changes in the levels of relevant MEP pathway transcripts, proteins, or enzyme activities. This mutant was found to be a new loss-of-function allele of PRL1 （Pleiotropic Regulatory Locus 1）, a gene encoding a conserved WD-protein that functions as a global regulator of sugar, stress, and hormone responses, in part by inhibition of SNFl-related protein kinases （SnRK1）. Consistent with the reported role of SnRK1 kinases in the phosphorylation and inactivation of the main regulatory enzyme of the MVA pathway （hydroxymethylglutaryl coenzyme-A reductase）, its activity but not transcript or protein levels was reduced in prll seedlings. However, the accumulation of MVA-derived end products （sterols） was unaltered in mutant seedlings. Sucrose supplementation to wild- type seedlings phenocopied the prll mutation in terms of isoprenoid metabolism, suggesting that the observed isoprenoid phenotypes result from the increased sugar accumulation in the prll mutant. In summary, PRL1 appears to coordinate isoprenoid metabolism with sugar, hormone, and stress responses.展开更多
文摘Carotenoids are pigments required for photosynthesis, photoprotection and the production of carotenoid- derived hormones such as ABA and strigolactones. The carotenoid biosynthetic pathway bifurcates after lycopene to produce epsilon- and beta-carotenoids and this branch is critical for determining carotenoid composition. Here, we show how the branch point can be regulated by the chromatin-modifying histone methyltransferase, Set Domain Group 8 （SDG8） targeting the carotenoid isomerase （CRTISO）. SDG8 is required to maintain permissive expression of CRTISO during seedling development, in leaves, shoot apex, and some floral organs. The CRTISO and SDG8 promoters show overlapping tissue-specific patterns of reporter gene activity. Interestingly, CRTISO showed atypical reporter gene expression in terms of greater variability between different lines compared to the Cauliflower Mosaic Virus 35S promoter （CaMV35s） and ~LCY promoters, potentially due to chromosomal position effects. Regulation of the CRTISO promoter was dependent in part upon the presence or absence of SDG8. Knockouts of SDG8 （carotenoid and chloroplast regulation （ccrl）） and CRTISO （ccr2） result in altered carotenoid composition and this could be restored in ccr2 using the CaMV35s or CRTISO promoters. In contrast, varying degrees of GUS expression and carotenoid complementation by CRTISO overexpression using CaMV35S or CRTISO promoters in the ccrl background demonstrated that both the CRTISO promoter and open reading frame are necessary for SDG8-mediated expression of CRTISO.
文摘The biosynthesis of isoprenoids in plant cells occurs from precursors produced in the cytosol by the mevalonate （MVA） pathway and in the plastid by the methylerythritol 4-phosphate （MEP） pathway, but little is known about the mechanisms coordinating both pathways. Evidence of the importance of sugar signaling for such coordination in Arabi- dopsis thaliana is provided here by the characterization of a mutant showing an increased accumulation of MEP-derived isoprenoid products （chlorophylls and carotenoids） without changes in the levels of relevant MEP pathway transcripts, proteins, or enzyme activities. This mutant was found to be a new loss-of-function allele of PRL1 （Pleiotropic Regulatory Locus 1）, a gene encoding a conserved WD-protein that functions as a global regulator of sugar, stress, and hormone responses, in part by inhibition of SNFl-related protein kinases （SnRK1）. Consistent with the reported role of SnRK1 kinases in the phosphorylation and inactivation of the main regulatory enzyme of the MVA pathway （hydroxymethylglutaryl coenzyme-A reductase）, its activity but not transcript or protein levels was reduced in prll seedlings. However, the accumulation of MVA-derived end products （sterols） was unaltered in mutant seedlings. Sucrose supplementation to wild- type seedlings phenocopied the prll mutation in terms of isoprenoid metabolism, suggesting that the observed isoprenoid phenotypes result from the increased sugar accumulation in the prll mutant. In summary, PRL1 appears to coordinate isoprenoid metabolism with sugar, hormone, and stress responses.
