Characterization of a cinnamoyl-CoA reductase 1 (CCR1) mutant in maize: effects on lignification, fibre development, and global gene expression

Abstract

Cinnamoyl-CoA reductase (CCR), which catalyses the first committed step of the lignin-specific branch of monolignol biosynthesis, has been extensively characterized in dicot species, but few data are available in monocots. By screening a Mu insertional mutant collection in maize, a mutant in the CCR1 gene was isolated named Zmccr1–. In this mutant, CCR1 gene expression is reduced to 31% of the residual wild-type level. Zmccr1– exhibited enhanced digestibility without compromising plant growth and development. Lignin analysis revealed a slight decrease in lignin content and significant changes in lignin structure. p-Hydroxyphenyl units were strongly decreased and the syringyl/guaiacyl ratio was slightly increased. At the cellular level, alterations in lignin deposition were mainly observed in the walls of the sclerenchymatic fibre cells surrounding the vascular bundles. These cell walls showed little to no staining with phloroglucinol. These histochemical changes were accompanied by an increase in sclerenchyma surface area and an alteration in cell shape. In keeping with this cell type-specific phenotype, transcriptomics performed at an early stage of plant development revealed the down-regulation of genes specifically associated with fibre wall formation. To the present authors’ knowledge, this is the first functional characterization of CCR1 in a grass species.

Complete Proteomic-Based Enzyme Reaction and Inhibition Kinetics Reveal How Monolignol Biosynthetic Enzyme Families Affect Metabolic Flux and Lignin in Populus trichocarpa

“…The reduced flux would lead to an increase in S/G ratio and a reduction in lignin content (Figures 7F,7P,and 8K). This prediction is consistent with transgenic tobacco, alfalfa, maize, and Arabidopsis mutants Tu et al, 2010;Tamasloukht et al, 2011). When the abundance of CAD proteins is reduced, the PKMF model predicts a severe reduction in both S and G monolignol synthesis ( Figures 7J and 7T), and as result, lignin content is reduced.…”

Breeding maize for silage and biofuel production, an illustration of a step forward with the genome sequence

“…In bin 1.07, the ZmCCR1 gene, of which role in lignification has been clearly established [114,115] , was exactly located at the estimated QTL position. The 4CL2 gene also colocalized in this position, but this gene is likely not importantly dedicated to lignin biosynthesis.…”

“…Later, maize mutants obtained from transposon tagging collections [152] will allow to highlight their role in the IVNDFD traits and simultaneously to make available alleles that can be directly used in breeding programs, as the deregulated CCR1 allele resulting from a transposon insertion in the gene first intron [114]. Candidate gene validation could also be based on maize deregulated plants, underor over-expressing the investigated gene, and similarly making new germplasm available for plant improvement.…”

Genetic Determinants for Enzymatic Digestion of Lignocellulosic Biomass Are Independent of Those for Lignin Abundance in a Maize Recombinant Inbred Population

“…Overall, for our lignin/4-vinylphenol QTL, 15 genes involved in monolignol synthesis or polymerization were differentially expressed at least 5-fold in B73 as compared with Mo17; only five of the monolignol genes within the saccharification yield QTL differed by 5-fold or more (Supplemental Table S6). Alteration of the activity of any of these genes, either through mutation or reduced expression of the genes by RNA interference, can impact lignin abundance (Ma, 2007;Fu et al, 2011a;Saathoff et al, 2011;Tamasloukht et al, 2011;Saballos et al, 2012).…”