Cacao producers suffer significant losses due to a variety of pathogens.
Development of disease resistant cacao varieties is an essential strategy to
combat this threat, but is limited by sources of genetic resistance and the
slow generation time of this crop. Andrew Fister of Pennsylvania State
University and colleagues present the first application of CRISPR-Cas9
genome editing technology in cacao leaves and cotyledon cells.

As a proof of concept, Fister's team targeted the cacao Non-Expressor of
Pathogenesis-Related 3 (TcNPR3) gene, a potential suppressor of defense
response. The team later identified the presence of mutations in ~30% of
TcNPR3 copies in the treated tissues. The edited tissue exhibited an
increased resistance to the cacao pathogen Phytophthora tropicalis.
Downstream defense genes were also found to be upregulated. Analysis of
off-target mutations did not reveal unwanted mutations.

These results confirm the function of NPR3 as a repressor of the cacao
immune system and demonstrate the application of CRISPR-Cas9 as a genomic
tool for cacao. Further studies will test the effectiveness of this tool at
a whole plant level.



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