Evaluation of off-target effects of the Cas9 in a knock-out Phaeodactylum tricornutum strain. Phaeodactylum tricornutum strain:Pt1

We used the combination of CRISPR/Cas9 and bacterial conjugation to edit thePhatr3_J46193 gene in the P. tricornutum genome. Since there are no reports of the occurrence of off-target changes at the genome level in microalgae, we performed whole-genome Illumina sequencing ascertaining that the target locus was affected by two different deletions in the two alleles, while a phenomenon of gene conversion was found in other three regions in the genome, probably due to a mechanism of homologous recombination, that caused loss of heterozygosity at the corresponding genomicregions.