Sugarcane is the world's most efficient feedstock for commercial production
of bioethanol. In previous studies, RNAi suppression of the lignin
biosynthetic gene, caffeic acid O-methyltransferase (COMT) have improved
ethanol production from lignocellulosic biomass. However, sugarcane's highly
polyploid genome presents quite a challenge for genetic modification
techniques. Baskaran Kannan of University of Florida in the US targeted COMT
with a single pair of Transcription Activator-Like Effector Nuclease (TALEN)
for multi-allelic mutagenesis to modify lignin biosynthesis in sugarcane.
COMT mutants showed up to 19.7% lignin reduction and had significantly
improved saccharification efficiency. Biomass production of COMT mutant
lines with superior saccharification efficiency also did not differ
significantly from the original cultivar under replicated field conditions.
Analysis revealed that mutations in 107 of the 109 COMT copies in the
progeny of mutant lines using a single TALEN pair. The mutant line combined
altered cell wall composition and greatly improved saccharification
efficiency with good agronomic performance.
This study confirms the feasibility of mutating a very large number of
target alleles for improvement of crops with complex genomes.