There is an urgent need to reduce our dependency on fossil fuels, and to reduce
greenhouse gas (GHG) emissions. In recent years, a conversion of lignocellulosic
biomass from agricultural wastes to biofuel has been considered a promising solution
to provide sustainable liquid fuels without competing with food production. At
present, this is limited by the cost effectiveness of the production process, due to the
recalcitrance of lignocellulosic biomass to digestion. One way to tackle this problem
is to improve the digestibility of the biomass feedstock itself, which would help to
decrease chemical and enzyme treatments necessary for converting biomass to
fermentable sugars for bioethanol production. With this objective in mind, the aim of
this study is to identify genes that affect the digestibility of rice straw. Rice (Oryza
sativa), the third biggest cereal crop in the world, has a small diploid genome, and
well-developed molecular genetic tools to underpin the use of Genome Wide
Association Studies (GWAS), a powerful tool for identifying quantitative trait loci. The genotypic data of 151 varieties, containing 328,915 Single Nucleotide
Polymorphism (SNPs), was analysed together with the phenotypic data from three
different cell wall characterisation assays: (1) saccharification, (2) total lignin
content, and (3) silica measurement by by X-ray fluorescence. This resulted in the
identification of 10 significant QTL for saccharification potential, 3 significant QTL
for Silica content, and 8 significant QLTs for total Lignin. The digestibility QTL
regions identified include three strong potential candidate genes which determine on
digestibility: OsAT10 (Bartley, et al., 2013); OsIRX9 (Chiniquy, et al., 2013); and
OsMYB58/63-L (Noda, et al., 2015). A strong correlation between silicon content
and digestibility was also identified. A QTL in chromosome 6 occurred in both
GWAS for digestibility and silica, and revealed a contrasting bi-allelic effect
between the amounts of sugar released and silica content. The OsAT10 gene, located
in this common QTL region was validated using the straw from overexpression lines,
showing that OsAT10 had large effect on both silica content and digestibility.
