Dissecting phytoplasma effector adaptation to plant targets (Bilateral BBSRC-FAPESP application)

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Phytoplasmas are intracellular bacterial pathogens of plants that are transmitted by insect vectors. They induce a variety of symptoms in plants and crops, such as witches' brooms (increased lateral branching) and phyllody (flowers reverting into leaves that remain sterile). Phytoplasmas can negatively impact crop production in many regions of the world. They interfere with flower production and decline fruit/grain yields, a problem in maize, fruit trees, grapevines, coconut etc. Because phytoplasmas are insect-transmitted, their occurrence is expanding as the climate warms up and pesticide use is being restricted. The Hogenhout (SH) group at The John Innes Centre has made significant progress with phytoplasma pathogenesis and their impact on host plants. This group found that phytoplasmas produce specific virulence proteins (effectors), which interact with conserved plant proteins leading to crinkled leaves, increased lateral branching (witches' brooms) and the downregulation of plant defence responses to the phytoplasma insect vectors. The latter leads to a greater number of insect vectors that transmit the phytoplasma to other plants. So far, the SH group has focused on phytoplasma interactions with the model plant Arabidopsis thaliana. In this project, the SH group will collaborate with the Spotti-Lopes (JSL) group at The University of Sao Paulo in Brazil who has studied the ecology and epidemiology of an important phytoplasma disease agent of maize. This pathogen causes maize bushy stunt disease and is transmitted by the corn leafhopper, which builds up to high population levels in maize fields in Brazil, Argentina and Mexico, therefore triggering severe phytoplasma epidemics. Maize bushy stunt phytoplasma and the corn leafhopper have co-evolved with the domestication of maize from its wild progenitor, teosinte, and hence are well adapted to colonize maize. Phytoplasma-infected maize plants typically produce more primary and secondary lateral branches (hence, the name maize bushy stunt phytoplasma), fewer ears and lower grain yields. These infected plants may support a greater number of corn leafhoppers that transmit maize bushy stunt phytoplasma to other maize plants. Together the SH and JSL group will translate the knowledge from the phytoplasma-Arabidopsis system to investigate maize bushy stunt phytoplasma and the corn leafhopper in maize. More specifically, we will determine if a maize bushy stunt phytoplasma effector protein induces the increased branching and reduced grain yield symptoms typically observed in phytoplasma-infected maize. Moreover, we will determine of this effector suppresses plant immunity to the corn leafhopper leading to greater leafhopper populations. We will also investigate the genomic variation of maize bushy stunt phytoplasmas in Brazil. Finally, we will assess if we can generate maize varieties that are not targeted by the phytoplasma effector protein leading to a reduction in maize bushy stunt symptoms and increased grain production during phytoplasma epidemics. We will collaborate with the agricultural company Dow Agrosciences. This project will provide exchange visits and a learning platform for all staff involved. Overall this work will increase our fundamental understanding of how pathogen virulence factors (effectors) adapt to host targets thereby facilitating pathogen colonization of these hosts and pathogen dispersal by insect vectors.