Dynamics of Lignin Pathway Gene Expression During Maize Development.

Grass cell walls are a major source of animal feed and a potential feedstock for biofuels, and are mainly composed of lignocellulosic material. Lignin is a major determinant of biomass quality primarily because it physically obstructs the accessibility of cell wall polysaccharides to hydrolytic enzymes. Understanding the spatial and temporal expression patterns of genes involved in lignin biosynthesis is therefore crucial for improving maize and related grasses for silage and biofuels. We used a NimbleGen microarray to study the expression of lignin pathway genes in diverse tissues of maize inbred B73. Expression of lignin pathway genes varied according to tissue age and type. Expression profile of roots was unique compared aboveground plant parts, and reproductive organs (cob, tassel, silk) were distinct from vegetative organs (leaves, internodes). Within an organ group, the expression profiles were affected by the developmental stage; most lignin genes had relatively higher expression in the immature organs indicating active lignification during secondary cell wall formation in developing tissues. Striking expression differences were observed among paralogs; while some gene family members were constitutively expressed, others were specific to certain organs/developmental stages. This suggests that expansion of the genes families in maize is accompanied by diversification in transcriptional regulation and, in some cases, subfunctionalization. Association of gene expression with metabolic profiles of selected tissues will be presented. This information will be an excellent resource for targeted modification of the lignin pathway in maize to improve biomass quality for agricultural and industrial use.