The genome biology of phytoplasma: modulators of plants and insects

Phytoplasmas are bacterial pathogens of plants that are transmitted by insects. These bacteria uniquely multiply intracellularly in both plants (Plantae) and insects (Animalia). Similarly to bacterial endosymbionts, phytoplasmas have reduced genomes with limited metabolic capabilities. Nonetheless, the chromosomes of many phytoplasmas are rich in repeated DNA consisting of mobile elements. Phytoplasmas produce an arsenal of effectors most of which are encoded on these mobile elements and on plasmids. These effectors target conserved plant transcription factors resulting in witches’ broom and leafy flower symptoms and suppression of plant defense to insect vectors that transmit the phytoplasmas. Future studies of these fascinating microbes will generate a wealth of new knowledge about forces that shape genomes and microbial interactions with multicellular hosts.

► Phytoplasmas have dual-host life cycles involving plants and insects. ► Phytoplasmas have reduced genomes rich in mobile genetic elements. ► The majority of phytoplasma effector genes lie on mobile genetic elements. ► Phytoplasma effectors alter plant development and aid insect colonization. ► Phytoplasma effectors suppress plant defense to insects.