Horizontal gene transfer
The C. panzhihuaensis genome contains four copies of an
insecticidal toxin gene family named fit D that was acquired via
ancient horizontal transfer from fungi (Lui et al ., 2022). Thesefit D genes encode proteins similar to the fit toxin and MCF toxin
of Photorhabdus bacteria, which are lethal to insects.
Experimental injection of the synthesized C. panzhihuaensis FitD
protein into moth larvae resulted in significantly higher mortality than
controls, demonstrating that this protein provides resistance against at
least some insect herbivores. Phylogenetic analyses indicate thefitD gene family originated from bacteria and the cycad sequences
share a common ancestor with fungi fit D with subsequent gene
family expansion in the ancestor of C. panzhihuaensis andCycas debaoensis . The acquisition of this toxin gene family
represents an important innovation that likely enhanced the defense
capacities of Cycas against insect pests and illustrates how
horizontal transfer of foreign genes can provide adaptive benefits.