The structurally robust biopolymer sporopollenin is the major constituent of the exine layer of pollen wall and plays a vital role in plant reproductive success.The sporopollenin precursors are synthesized through an ...The structurally robust biopolymer sporopollenin is the major constituent of the exine layer of pollen wall and plays a vital role in plant reproductive success.The sporopollenin precursors are synthesized through an ancient polyketide biosynthetic pathway consisting of a series of anther-specific enzymes that are widely present in all land plant lineages.Tetraketideα-pyrone reductase 1(TKPR1)and TKPR2 are two reductases catalyzing the final reduction of the carbonyl group of the polyketide synthase-synthesized tetraketide intermediates to hydroxylatedα-pyrone compounds,important precursors of sporopollenin.In contrast to the functional conservation of many sporopollenin biosynthesis associated genes confirmed in diverse plant species,TKPR2’s role has been addressed only in Arabidopsis,where it plays a minor role in sporopollenin biosynthesis.We identified in gerbera two non-anther-specific orthologues of AtTKPR2,Gerbera reductase 1(GRED1)and GRED2.Their dramatically expanded expression pattern implies involvement in pathways outside of the sporopollenin pathway.In this study,we show that GRED1 and GRED2 are still involved in sporopollenin biosynthesis with a similar secondary role as AtTKPR2 in Arabidopsis.We further show that this secondary role does not relate to the promoter of the gene,AtTKPR2 cannot rescue pollen development in Arabidopsis even when controlled by the AtTKPR1 promoter.We also identified the gerbera orthologue of AtTKPR1,GTKPR1,and characterized its crucial role in gerbera pollen development.GTKPR1 is the predominant TKPR in gerbera pollen wall formation,in contrast to the minor roles GRED1 and GRED2.GTKPR1 is in fact an excellent target for engineering male-sterile gerbera cultivars in horticultural plant breeding.展开更多
Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and perox...Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and peroxidases contribute to lignin biosynthesis in muro is under active evaluation. We performed an in silico study of Norway spruce （Picea abies （L.） Karst.） laccases utilizing available genomic data. As many as 292 laccase encoding sequences （genes, gene fragments, and pseudogenes） were detected in the spruce genome. Out of the 112 genes annotated as laccases, 79 are expressed at some level. We isolated five fun-length laccase cDNAs from developing xylem and an extracellular lignin-forming cell culture of spruce. In addition, we purified and biochemically characterized one culture medium laccase from the lignin-forming cell culture. This laccase has an acidic pH optimum （pH 3.8-4.2） for coniferyl alcohol oxidation. It has a high affinity to coniferyl alcohol with an apparent Km value of 3.5μM; however, the laccase has a lower catalytic efficiency （Vmax/Km） for coniferyl alcohol oxidation compared with some purified culture medium peroxidases. The properties are discussed in the context of the information already known about laccases/coniferyl alcohol oxidases of coniferous plants.展开更多
文摘The structurally robust biopolymer sporopollenin is the major constituent of the exine layer of pollen wall and plays a vital role in plant reproductive success.The sporopollenin precursors are synthesized through an ancient polyketide biosynthetic pathway consisting of a series of anther-specific enzymes that are widely present in all land plant lineages.Tetraketideα-pyrone reductase 1(TKPR1)and TKPR2 are two reductases catalyzing the final reduction of the carbonyl group of the polyketide synthase-synthesized tetraketide intermediates to hydroxylatedα-pyrone compounds,important precursors of sporopollenin.In contrast to the functional conservation of many sporopollenin biosynthesis associated genes confirmed in diverse plant species,TKPR2’s role has been addressed only in Arabidopsis,where it plays a minor role in sporopollenin biosynthesis.We identified in gerbera two non-anther-specific orthologues of AtTKPR2,Gerbera reductase 1(GRED1)and GRED2.Their dramatically expanded expression pattern implies involvement in pathways outside of the sporopollenin pathway.In this study,we show that GRED1 and GRED2 are still involved in sporopollenin biosynthesis with a similar secondary role as AtTKPR2 in Arabidopsis.We further show that this secondary role does not relate to the promoter of the gene,AtTKPR2 cannot rescue pollen development in Arabidopsis even when controlled by the AtTKPR1 promoter.We also identified the gerbera orthologue of AtTKPR1,GTKPR1,and characterized its crucial role in gerbera pollen development.GTKPR1 is the predominant TKPR in gerbera pollen wall formation,in contrast to the minor roles GRED1 and GRED2.GTKPR1 is in fact an excellent target for engineering male-sterile gerbera cultivars in horticultural plant breeding.
基金supported by University of Helsinki Research Funds (to A.K.)Academy of Finland (grant 251390 to A.K.)Societas pro Fauna et Flora Fennica (to H.A.M.)
文摘Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and peroxidases contribute to lignin biosynthesis in muro is under active evaluation. We performed an in silico study of Norway spruce （Picea abies （L.） Karst.） laccases utilizing available genomic data. As many as 292 laccase encoding sequences （genes, gene fragments, and pseudogenes） were detected in the spruce genome. Out of the 112 genes annotated as laccases, 79 are expressed at some level. We isolated five fun-length laccase cDNAs from developing xylem and an extracellular lignin-forming cell culture of spruce. In addition, we purified and biochemically characterized one culture medium laccase from the lignin-forming cell culture. This laccase has an acidic pH optimum （pH 3.8-4.2） for coniferyl alcohol oxidation. It has a high affinity to coniferyl alcohol with an apparent Km value of 3.5μM; however, the laccase has a lower catalytic efficiency （Vmax/Km） for coniferyl alcohol oxidation compared with some purified culture medium peroxidases. The properties are discussed in the context of the information already known about laccases/coniferyl alcohol oxidases of coniferous plants.
