Phenylpropanoid Biosynthesis Gene Expression Precedes Lignin Accumulation During Shoot Development in Lowland and Upland Switchgrass Genotypes

Efficient conversion of lignocellulosic biomass into biofuels is influenced by biomass composition and structure. Lignin and other cell wall phenylpropanoids, such as para-coumaric acid (pCA) and ferulic acid (FA), reduce cell wall sugar accessibility and hamper biochemical fuel production. Toward identifying the timing and key parameters of cell wall recalcitrance across different switchgrass genotypes, this study measured cell wall composition and lignin biosynthesis gene expression in three switchgrass genotypes, A4 and AP13, representing the lowland ecotype, and VS16, representing the upland ecotype, at three developmental stages [Vegetative 3 (V3), Elongation 4 (E4), and Reproductive 3 (R3)] and three segments (S1–S3) of the E4 stage under greenhouse conditions. A decrease in cell wall digestibility and an increase in phenylpropanoids occur across development. Compared with AP13 and A4, VS16 has significantly less lignin and greater cell wall digestibility at the V3 and E4 stages; however, differences among genotypes diminish by the R3 stage. Gini correlation analysis across all genotypes revealed that lignin and pCA, but also pectin monosaccharide components, show the greatest negative correlations with digestibility. Lignin and pCA accumulation is delayed compared with expression of phenylpropanoid biosynthesis genes, while FA accumulation coincides with expression of these genes. The different cell wall component accumulation profiles and gene expression correlations may have implications for system biology approaches to identify additional gene products with cell wall component synthesis and regulation functions.

Responses of Maize Internode to Water Deficit Are Different at the Biochemical and Histological Levels

Maize feeding value is strongly linked to plant digestibility. Cell wall composition and structure can partly explain cell wall digestibility variations, and we recently showed that tissue lignification and lignin spatial distribution also contribute to cell wall digestibility variations. Although the genetic determinism of digestibility and cell wall composition has been studied for more than 20 years, little is available concerning that of tissue lignification. Moreover, maize yield is negatively impacted by water deficit, and we newly highlighted the impact of water deficit on cell wall digestibility and composition together with tissue lignification. Consequently, the aim of this study was to explore the genetic mechanisms of lignin distribution in link with cell wall composition and digestibility under contrasted water regimes. Maize internodes from a recombinant inbred line (RIL) population grown in field trials with contrasting irrigation scenarios were biochemically and histologically quantified. Results obtained showed that biochemical and histological traits have different response thresholds to water deficit. Histological profiles were therefore only modified under pronounced water deficit, while most of the biochemical traits responded whatever the strength of the water deficit. Three main clusters of quantitative trait locus (QTL) for histological traits were detected. Interestingly, overlap between the biochemical and histological clusters is rare, and one noted especially colocalizations between histological QTL/clusters and QTL for p-coumaric acid content. These findings reinforce the suspected role of tissue p-coumaroylation for both the agronomic properties of plants as well as their digestibility.

Potentials to breed for improved fibre digestibility in temperate Czech maize (Zea mays L.) germplasm

Cell wall digestibility is an important quality trait of modern silage maize cultivars. The symbiotic relationship between microbes and ruminant livestock enables the efficient upcycling of otherwise for human consumption unsuitable rumen digestible fibre or cell wall components into highly nutritious milk and meat. Before entering the Czech National List of Plant Varieties, new silage maize germplasm is extensively tested for different cell wall digestibility parameters. Recently published, the undigestible neutral detergent fibre (uNDF) cell wall digestibility approach promises even greater practical relevance. The aim of our study was, therefore, to assess the potential of the uNDF method, compared with current standard procedures, using a vast set of official Czech plant variety trial evaluations and Czech silage analyses from the 2018 cropping season. The uNDF method yielded a twice as high phenotypic standard deviation, compared with the current standard approaches. This is good news for plant breeders, official variety testing organisations, and farm professionals alike, enabeling faster variety improvement and simpler variety selection. On the other hand, due to the low differentiation potential, we discourage the use of the absolute lignin content when selecting for digestible silage maize varieties. Since between the digestibility traits enzymatic soluble organic substance (ELOS) and cellulase digestibility (DCS), a Pearson correlation close to one was observed, the substitution of one of these analytics by the uNDF method, may render valuable additional information in a highly economical manner.