Fig. 6.

Classification of Lon homologs based on the structure of the SSD domain. Bacteria and animal SSD domains out-group from plants and fungi preserving a minimal structure. In the plant lineage, only helianthus and papaya that grouped together with most algae and fungi preserved a single gene with a Lon1-type SSD domain. Among Rosids, Brassicales in particular retained one gene copy with a Lon1-type structure and evolved copies with the Lon4-type SSD domain. The majority of land plants acquired the Lon4-type SSD domain.