Enzyme-Enzyme Interactions in Monolignol Biosynthesis

Abstract

The enzymes that comprise the monolignol biosynthetic pathway have been studied intensively for more than half a century. A major interest has been the role of pathway in the biosynthesis of lignin and the role of lignin in the formation of wood. The pathway has been typically conceived as linear steps that convert phenylalanine into three major monolignols or as a network of enzymes in a metabolic grid. Potential interactions of enzymes have been investigated to test models of metabolic channeling or for higher order interactions. Evidence for enzymatic or physical interactions has been fragmentary and limited to a few enzymes studied in different species. Only recently the entire pathway has been studied comprehensively in any single plant species. Support for interactions comes from new studies of enzyme activity, co-immunoprecipitation, chemical crosslinking, bimolecular fluorescence complementation, yeast 2-hybrid functional screening, and cell type–specific gene expression based on light amplification by stimulated emission of radiation capture microdissection. The most extensive experiments have been done on differentiating xylem of Populus trichocarpa, where genomic, biochemical, chemical, and cellular experiments have been carried out. Interactions affect the rate, direction, and specificity of both 3 and 4-hydroxylation in the monolignol biosynthetic pathway. Three monolignol P450 mono-oxygenases form heterodimeric and heterotetrameric protein complexes that activate specific hydroxylation of cinnamic acid derivatives. Other interactions include regulatory kinetic control of 4-coumarate CoA ligases through subunit specificity and interactions between a cinnamyl alcohol dehydrogenase and a cinnamoyl-CoA reductase. Monolignol enzyme interactions with other pathway proteins have been associated with biotic and abiotic stress response. Evidence challenging or supporting metabolic channeling in this pathway will be discussed.

Hunting monolignol transporters: membrane proteomics and biochemical transport assays with membrane vesicles of Norway spruce

“…Eight out of these 14 genes (PAL, C3H, three C4Hs, COMT, and two CCoAOMTs) were detected in the membrane proteomic data ( Table 3 ). It is interesting to hypothesize that a proportion of the proteins encoded by the co-expressed genes could function in association with the endoplasmic reticulum (ER), or with other ER proteins, as discussed by Wang et al (2019) . C4H/C3H function as homo- and heteromers associated with the ER ( Chen et al , 2011 ; Bassard et al , 2012 ), and some PAL enzymes associate with C4H ( Achnine et al , 2004 ).…”

Maize ZmFNSI Homologs Interact with an NLR Protein to Modulate Hypersensitive Response

“…This interaction, together with the interaction between HCT and CCoAOMT2 [21], may reflect the formation of a metabolon, a complex formed between sequential enzymes of a metabolic pathway believed to facilitate metabolite processing [54]. Components of the phenylpropanoid pathway have been shown to associate with each other in poplar and other species [55].…”

Regulation of Lignin Biosynthesis by Post-translational Protein Modifications

“…Lignification is also regulated at the enzyme level. Monolignol biosynthetic enzymes can directly interact with each other (e.g., Ptr4CL3-Ptr4CL5, PtrC3H-PtrC4H, At4CL1-AtC3H, At4CL1-AtC4H, and AtCCR1-AtC4H interactions) ( Chen et al, 2011 ; Chen H. -C. et al, 2014 ; Gou et al, 2018 ; Wang et al, 2019a ) or indirectly through common mediators such as AtMSPBs (e.g., AtC3H-AtMSPBs, AtC4H-AtMSPBs, AtF5H-AtMSPBs interactions) ( Gou et al, 2018 ). In addition, monolignol biosynthetic enzymes can interact with proteins in other biological pathways (e.g., OsCCR1-OsRac1, ZmCCoAOMT/ZmHCT-ZmRp1 interactions) ( Kawasaki et al, 2006 ; Wang G. H. et al, 2015 ; Wang and Balint-Kurti, 2016 ).…”

“…In addition, monolignol biosynthetic enzymes can interact with proteins in other biological pathways (e.g., OsCCR1-OsRac1, ZmCCoAOMT/ZmHCT-ZmRp1 interactions) ( Kawasaki et al, 2006 ; Wang G. H. et al, 2015 ; Wang and Balint-Kurti, 2016 ). These interactions may modulate enzyme stability, activity, and metabolic flux in lignin biosynthesis, increase the biosynthesis of lignin in response to pathogen infection, and suppress plant hypersensitive response ( Kawasaki et al, 2006 ; Chen et al, 2011 ; Chen H. -C. et al, 2014 ; Wang G. H. et al, 2015 ; Wang et al, 2019a ; Wang and Balint-Kurti, 2016 ; Gou et al, 2018 ). However, the role of post-translational modifications (PTMs) in SCW formation remains poorly understood.…”