The CRISPR-Cas9 system has allowed the possibility to engineer targeted
mutations in eukaryotic genomes. However, the efficiency of mutagenesis and
the generation of off-target mutations vary greatly between different
organisms. Chantal LeBlanc of Yale University now reports that plants
subjected to heat stress at 37°C show higher frequencies of CRISPR-induced
mutations compared to plants grown at the standard temperature of 22°C.

LeBlanc's team found that targeted mutagenesis by CRISPR-Cas9 in Arabidopsis
has increased by approximately five times in somatic tissues and up to 100
times in germlines upon heat treatment. This effect of temperature on the
mutation rate was also found to be not limited to Arabidopsis, as a similar
increase was observed in CRISPR-edited Citrus plants exposed to heat stress
at 37°C.

Analysis revealed that the Cas9 protein from Streptococcus pyogenes (SpCas9)
was more active in creating double-stranded DNA breaks at 37°C than at 22°C,
indicating a potential contributing mechanism for the effect of temperature
on CRISPR-Cas9.

This study reveals the importance of temperature in improving SpCas9
activity in eukaryotes, and provides a simple method to increase on-target
mutagenesis in plants using CRISPR-Cas9.

[onlinelibrary.wiley.com]