Molecular mechanisms of plant manipulation by secreting effectors of phytoplasmas

Phytoplasmas (genus 'Candidatus Phytoplasma') are plant pathogenic bacteria that reside intracellularly within the plant phloem. Phytoplasmas induce a wide range of unique symptoms, including phyllody, yellowing, dwarfing, witches' broom and purple tops. Phytoplasma diseases cause great damage to agricultural production and forest trees. Although there is an agricultural need to develop effective methods to control phytoplasma diseases, phytoplasmas are still one of the most poorly characterized groups of plant pathogens. Despite their small genomes, phytoplasmas induce unique symptoms to host plants, thus how phytoplasmas manipulate plants has been of interest. Since phytoplasmas are cell wall-less and reside inside of host cells, their secreting proteins via Sec system function in the cytoplasm of the host plant cell and are predicted to have some important roles in host-parasite interactions and/or virulence as effector proteins. Although the molecular mechanisms behind the symptoms are not fully understood, several secreting effector proteins of phytoplasmas have been shown to induce the symptoms or manipulate the host factors. In this review, we summarize the molecular mechanisms by which phytoplasma effector proteins manipulate plants. Phytoplasma effectors have been found to have a wide variety of functions, such as regulating plant morphogenesis and attracting insect vectors. Since these plant manipulations are thought to be essential for phytoplasma survival strategies, the inhibition of effector proteins could lead to control of phytoplasma infection.

Automated summary

Phytoplasmas are plant pathogenic bacteria that reside within the plant phloem. They cause a wide range of unique symptoms and have significant impacts on agricultural production and forest trees.