Chlorophyll(Chl)is essential for photosynthetic reactions and chloroplast development.While the enzymatic pathway for Chl biosynthesis is well established,the regulatory mechanism underlying the homeostasis of Chl lev...Chlorophyll(Chl)is essential for photosynthetic reactions and chloroplast development.While the enzymatic pathway for Chl biosynthesis is well established,the regulatory mechanism underlying the homeostasis of Chl levels remains largely unknown.In this study,we identified CBD1(Chlorophyll Biosynthetic Defect1),which functions in the regulation of chlorophyll biosynthesis.The CBD1 gene was expressed specifically in green tissues and its protein product was embedded in the thylakoid membrane.Furthermore,CBD1 was precisely co-expressed and functionally correlated with GUN5(Genome Uncoupled 5).Analysis of chlorophyll metabolic intermediates indicated that cbd1 and cbd1gun5 mutants over-accumulatedmagnesium protoporphyrin Ⅸ(Mg-Proto Ⅸ).In addition,the cbd1 mutant thylakoid contained less Mg than the wild type not only as a result of lower Chl content,but also implicating CBD1 in Mg transport.This was supported by the finding that CBD1 complemented a Mg^(2+)uptake-deficient Salmonella strain under low Mg conditions.Taken together,these results indicate that CBD1 functions synergistically with CHLH/GUN5 in Mg-Proto IX processing,and may serve as a Mg-transport protein to maintain Mg homeostasis in the chloroplast.展开更多
acid （ABA） is the key plant stress hormone. Consistent with the earlier studies in support of the presence of both membrane- and cytoplasm-localized ABA receptors, recent studies have identified multi- ple ABA recep...acid （ABA） is the key plant stress hormone. Consistent with the earlier studies in support of the presence of both membrane- and cytoplasm-localized ABA receptors, recent studies have identified multi- ple ABA receptors located in various subcellular locations. These include a chloroplast envelope-localized receptor （the H subunit of Chloro- plast Mg2＋-chelatase/ABA Receptor）, two plasma membrane-localized receptors （G-protein Coupled Receptor 2 and GPCR-type G proteins）, and one cytosol/nucleus-localized Pyrabactin Resistant （PYR）/PYR-Like （PYL）/Regulatory Component of ABA Receptor 1 （RCAR）. Although the downstream molecular events for most of the identified ABA receptors are currently unknown, one of them, PYR/PYL/RCAR was found to directly bind and regulate the activity of a long-known central regulator of ABA signaling, the A-group protein phosphatase 2C （PP2C）. Together with the Sucrose Non-fermentation Kinase Subfamily 2 （SnRK2s） protein kinases, a central signaling complex （ABA-PYR-PP2Cs-SnRK2s） that is responsible for ABA signal perception and transduction is supported by abundant genetic, physiological, biochemical and structural evidence. The identification of multiple ABA receptors has advanced our understanding of ABA signal perception and transduction while adding an extra layer of complexity.展开更多
基金supported by the National Natural Science Foundation of China(grant no.31900220 to C.Z.,and 31770267 to W.L.)the National Science Foundation(MCB-1714795 to S.L.).
文摘Chlorophyll(Chl)is essential for photosynthetic reactions and chloroplast development.While the enzymatic pathway for Chl biosynthesis is well established,the regulatory mechanism underlying the homeostasis of Chl levels remains largely unknown.In this study,we identified CBD1(Chlorophyll Biosynthetic Defect1),which functions in the regulation of chlorophyll biosynthesis.The CBD1 gene was expressed specifically in green tissues and its protein product was embedded in the thylakoid membrane.Furthermore,CBD1 was precisely co-expressed and functionally correlated with GUN5(Genome Uncoupled 5).Analysis of chlorophyll metabolic intermediates indicated that cbd1 and cbd1gun5 mutants over-accumulatedmagnesium protoporphyrin Ⅸ(Mg-Proto Ⅸ).In addition,the cbd1 mutant thylakoid contained less Mg than the wild type not only as a result of lower Chl content,but also implicating CBD1 in Mg transport.This was supported by the finding that CBD1 complemented a Mg^(2+)uptake-deficient Salmonella strain under low Mg conditions.Taken together,these results indicate that CBD1 functions synergistically with CHLH/GUN5 in Mg-Proto IX processing,and may serve as a Mg-transport protein to maintain Mg homeostasis in the chloroplast.
文摘acid （ABA） is the key plant stress hormone. Consistent with the earlier studies in support of the presence of both membrane- and cytoplasm-localized ABA receptors, recent studies have identified multi- ple ABA receptors located in various subcellular locations. These include a chloroplast envelope-localized receptor （the H subunit of Chloro- plast Mg2＋-chelatase/ABA Receptor）, two plasma membrane-localized receptors （G-protein Coupled Receptor 2 and GPCR-type G proteins）, and one cytosol/nucleus-localized Pyrabactin Resistant （PYR）/PYR-Like （PYL）/Regulatory Component of ABA Receptor 1 （RCAR）. Although the downstream molecular events for most of the identified ABA receptors are currently unknown, one of them, PYR/PYL/RCAR was found to directly bind and regulate the activity of a long-known central regulator of ABA signaling, the A-group protein phosphatase 2C （PP2C）. Together with the Sucrose Non-fermentation Kinase Subfamily 2 （SnRK2s） protein kinases, a central signaling complex （ABA-PYR-PP2Cs-SnRK2s） that is responsible for ABA signal perception and transduction is supported by abundant genetic, physiological, biochemical and structural evidence. The identification of multiple ABA receptors has advanced our understanding of ABA signal perception and transduction while adding an extra layer of complexity.
