Phytoplasma adapt to the diverse environments of their plant and insect hosts by altering gene expression

•AY-WB phytoplasma gene expression in plants and insects was analysed by qRT-PCR.•74 and 34 genes were up-regulated in insects and plants, respectively.•Stress response and metabolism-related genes were up-regulated in insects.•Membrane-associated proteins genes were up-regulated in plants.

Phytoplasmas are intracellular insect-transmitted phytopathogenic bacteria with small genomes. To understand how Aster Yellows phytoplasma strain witches' broom (AY-WB) adapts to their hosts, we performed qRT-PCR analysis of 179 in silico functionally annotated AY-WB genes that are likely to have a role in host adaptation. 74 genes were up-regulated in insects and included genes involved in stress response, phospholipid synthesis, malate and pyruvate metabolism, hemolysin and transporter genes, multiple copies of thymidylate kinase, sigma factor and Zn-proteases genes. In plants, 34 genes encoding an immune dominant membrane protein, membrane-associated proteins, and multidrug resistance ABC-type transporters, were up-regulated. Differential regulation of gene expression thus appears to play an important role in host adaptation of phytoplasmas.