A large-scale forward genetic screen for maize mutants with altered lignocellulosic properties

Abstract

The development of efficient pipelines for the bioconversion of grass lignocellulosic feedstocks is challenging due to the limited understanding of the molecular mechanisms controlling the synthesis, deposition, and degradation of the varying polymers unique to grass cell walls. Here, we describe a large-scale forward genetic approach resulting in the identification of a collection of chemically mutagenized maize mutants with diverse alterations in their cell wall attributes such as crystalline cellulose content or hemicellulose composition. Saccharification yield, i.e. the amount of lignocellulosic glucose (Glc) released by means of enzymatic hydrolysis, is increased in two of the mutants and decreased in the remaining six. These mutants, termed candy-leaf (cal), show no obvious plant growth or developmental defects despite associated differences in their lignocellulosic composition. The identified cal mutants are a valuable tool not only to understand recalcitrance of grass lignocellulosics to enzymatic deconstruction but also to decipher grass-specific aspects of cell wall biology once the genetic basis, i.e. the location of the mutation, has been identified.

Keywords: cell wall; lignocellolusic biomass; maize; mutant; saccharification.

Figure 1

Saccharification of cal mutant seedlings. The values correspond to the mean ± SD (n = 5). cal1, cal2, bm1, and bm3 are in the B73 genetic background. cal3, cal4, cal5, cal6, cal7, and cal8 are in the A619 genetic background. dAIR destarched alcohol insoluble residue. Asterisks indicate levels of statistical significance between each mutant and corresponding wild-type plant determined by two-tailed unpaired Student t- test at p-value < 0.01 (**).

Figure 2

Saccharification yield of cal adult tissues. Amounts of glucose released from dAIR after 20-h enzymatic digestion from untreated (A) and NaOH-pretreated (B) mature leaves and stems. Values are means ± SD (n ≥ 3. Asterisks indicate significant differences from the wild type plants using the unpaired Student's t-test p-value < 0.05 (*); p-value < 0.01 (**).