期刊
OPEN BIOLOGY
卷 9, 期 12, 页码 -出版社
ROYAL SOC
DOI: 10.1098/rsob.190215
关键词
lignin; secondary cell wall; metabolic channelling; membrane transport; oxidative polymerization; reactive oxygen species
资金
- Center for Bioenergy Innovation, US DOE Bioenergy Research Center - Office of Biological and Environmental Research in the DOE Office of Science
- US National Science Foundation Integrated Organismal Systems program [1456286]
- Division Of Integrative Organismal Systems
- Direct For Biological Sciences [1456286] Funding Source: National Science Foundation
Lignin is a major component of secondarily thickened plant cell walls and is considered to be the second most abundant biopolymer on the planet. At one point believed to be the product of a highly controlled polymerization procedure involving just three potential monomeric components (monolignols), it is becoming increasingly clear that the composition of lignin is quite flexible. Furthermore, the biosynthetic pathways to the major monolignols also appear to exhibit flexibility, particularly as regards the early reactions leading to the formation of caffeic acid from coumaric acid. The operation of parallel pathways to caffeic acid occurring at the level of shikimate esters or free acids may help provide robustness to the pathway under different physiological conditions. Several features of the pathway also appear to link monolignol biosynthesis to both generation and detoxification of hydrogen peroxide, one of the oxidants responsible for creating monolignol radicals for polymerization in the apoplast. Monolignol transport to the apoplast is not well understood. It may involve passive diffusion, although this may be targeted to sites of lignin initiation/polymerization by ordered complexes of both biosynthetic enzymes on the cytosolic side of the plasma membrane and structural anchoring of proteins for monolignol oxidation and polymerization on the apoplastic side. We present several hypothetical models to illustrate these ideas and stimulate further research. These are based primarily on studies in model systems, which may or may not reflect the major lignification process in forest trees.
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