Cinnamoyl CoA reductase （CCR） and cinnamyl alcohol dehydrogenase （CAD） catalyze the last steps of mono- lignol biosynthesis. In Arabidopsis, one CCR gene （CCR1, Atlg15950） and two CAD genes （CAD C At3g19450 and...Cinnamoyl CoA reductase （CCR） and cinnamyl alcohol dehydrogenase （CAD） catalyze the last steps of mono- lignol biosynthesis. In Arabidopsis, one CCR gene （CCR1, Atlg15950） and two CAD genes （CAD C At3g19450 and CAD D At4g34230） are involved in this pathway. A triple cad c cad d ccrl mutant, named ccc, was obtained. This mutant displays a severe dwarf phenotype and male sterility. The lignin content in ccc mature stems is reduced to 50% of the wild-type level. In addition, stem lignin structure is severely affected, as shown by the dramatic enrichment in resistant inter-unit bonds and incorporation into the polymer of monolignol precursors such as coniferaldehyde, sinapaldehyde, and ferulic acid. Male sterility is due to the lack of lignification in the anther endothecium, which causes the failure of anther de- hiscence and of pollen release. The cc~ hypolignified stems accumulate higher amounts of flavonol glycosides, sinapoyl malate and feruloyl malate, which suggests a redirection of the phenolic pathway. Therefore, the absence of CAD and CCR, key enzymes of the monolignol pathway, has more severe consequences on the phenotype than the individual absence of each of them. Induction of another CCR （CCR2, Atlg80820） and another CAD （CAD1, At4g39330） does not compensate the absence of the main CCR and CAD activities. This lack of CCR and CAD activities not only impacts lignification, but also severely affects the development of the plants. These consequences must be carefully considered when trying to reduce the lignin content of plants in order to facilitate the lignocellulose-to-bioethanol conversion process.展开更多
The presence of lignin reduces the quality of lignocellulosic biomass for forage materials and feedstock for biofuels. In C4 grasses, the brown midrib phenotype has been linked to mutations to genes in the monolignol ...The presence of lignin reduces the quality of lignocellulosic biomass for forage materials and feedstock for biofuels. In C4 grasses, the brown midrib phenotype has been linked to mutations to genes in the monolignol biosynthesis pathway. For example, the Bmr6 gene in sorghum （Sorghum bicolor） has been previously shown to encode cinnamyl alcohol dehydrogenase （CAD）, which catalyzes the final step of the monolignol biosynthesis pathway. Mutations in this gene have been shown to reduce the abundance of lignin, enhance digestibility, and improve saccharification efficiencies and ethanol yields. Nine sorghum lines harboring five different bmr6 alleles were identified in an EMS-mutagenized TILLING population. DNA sequencing of Bmr6 revealed that the majority of the mutations impacted evolutionarily conserved amino acids while three-dimensional structural modeling predicted that all of these alleles interfered with the enzyme＇s ability to bind with its NAPPH cofactor. All of the new alleles reduced in vitro CAD activity levels and enhanced glucose yields following saccharification. Further, many of these lines were associated with higher reductions in acid detergent lignin compared to lines harboring the previously characterized bmr6-ref allele. These bmr6 lines represent new breeding tools for manipulating biomass composition to enhance forage and feedstock quality.展开更多
文摘Cinnamoyl CoA reductase （CCR） and cinnamyl alcohol dehydrogenase （CAD） catalyze the last steps of mono- lignol biosynthesis. In Arabidopsis, one CCR gene （CCR1, Atlg15950） and two CAD genes （CAD C At3g19450 and CAD D At4g34230） are involved in this pathway. A triple cad c cad d ccrl mutant, named ccc, was obtained. This mutant displays a severe dwarf phenotype and male sterility. The lignin content in ccc mature stems is reduced to 50% of the wild-type level. In addition, stem lignin structure is severely affected, as shown by the dramatic enrichment in resistant inter-unit bonds and incorporation into the polymer of monolignol precursors such as coniferaldehyde, sinapaldehyde, and ferulic acid. Male sterility is due to the lack of lignification in the anther endothecium, which causes the failure of anther de- hiscence and of pollen release. The cc~ hypolignified stems accumulate higher amounts of flavonol glycosides, sinapoyl malate and feruloyl malate, which suggests a redirection of the phenolic pathway. Therefore, the absence of CAD and CCR, key enzymes of the monolignol pathway, has more severe consequences on the phenotype than the individual absence of each of them. Induction of another CCR （CCR2, Atlg80820） and another CAD （CAD1, At4g39330） does not compensate the absence of the main CCR and CAD activities. This lack of CCR and CAD activities not only impacts lignification, but also severely affects the development of the plants. These consequences must be carefully considered when trying to reduce the lignin content of plants in order to facilitate the lignocellulose-to-bioethanol conversion process.
基金supported by the Office of Science (BER),U.S. Department of Energy grant DE-FG02-07ER64458 (Wilfred Vermerris and Scott E. Sattler)additional funding from USDA-ARS,CRIS project 5440-21220-032-00D (S.E.S,Deanna L. Funnell-Harris.)+2 种基金USDA AFRI grant number 2011-67009-30026 (S.E.S,D.L.F.H.)USDA Biomass Research and Development Initiative grant number 2011-10006-30358 (W.V.)the U.S. DOE’s International Affairs under award number DE-PI0000031 from the U.S. DOE’s Office of Energy Efficiency and Renewable Energy,Bioenergy Technologies Office (W.V)
文摘The presence of lignin reduces the quality of lignocellulosic biomass for forage materials and feedstock for biofuels. In C4 grasses, the brown midrib phenotype has been linked to mutations to genes in the monolignol biosynthesis pathway. For example, the Bmr6 gene in sorghum （Sorghum bicolor） has been previously shown to encode cinnamyl alcohol dehydrogenase （CAD）, which catalyzes the final step of the monolignol biosynthesis pathway. Mutations in this gene have been shown to reduce the abundance of lignin, enhance digestibility, and improve saccharification efficiencies and ethanol yields. Nine sorghum lines harboring five different bmr6 alleles were identified in an EMS-mutagenized TILLING population. DNA sequencing of Bmr6 revealed that the majority of the mutations impacted evolutionarily conserved amino acids while three-dimensional structural modeling predicted that all of these alleles interfered with the enzyme＇s ability to bind with its NAPPH cofactor. All of the new alleles reduced in vitro CAD activity levels and enhanced glucose yields following saccharification. Further, many of these lines were associated with higher reductions in acid detergent lignin compared to lines harboring the previously characterized bmr6-ref allele. These bmr6 lines represent new breeding tools for manipulating biomass composition to enhance forage and feedstock quality.
