The effectors that alter plant-insect interactions

Abstract

Effectors are defined as the molecules that are secreted by pathogens / parasites and alter the interactions of two or more organisms. In my previous laboratory (Saskia Hogenhout lab, John Innes Centre, UK), we have identified several effectors of Aster Yellows phytoplasma strain Witches’ Broom (AY-WB), which is a bacterial phytopathogen transmitted by leafhopper, Macrosteles quadrilineatus. One of the effectors, SAP11, interacts with Arabidopsis class II TCP transcription factors and destabilizes them. The class II TCPs regulate plant growth and production of jasmonic acid, which positively controls Arabidopsis defence against M. quadrilineatus. M. quadrilineatusproduces higher number of progenies on the Arabidopsis plants that express SAP11 compared to the control plants. Thus, AY-WB effector SAP11 down-regulates plant defence and promotes the production of leafhopper progenies, which are essential for dispersal of AY-WB in nature.

Aphids are sap-feeding insects and inject various saliva proteins into plants while they feed. Aphid saliva and some of the proteins secreted into saliva are reported to facilitate or interfere with aphid feeding and progeny production. Hence, there is an emerging concept that aphids secrete effector proteins into plants. The pea aphid (Acyrthosiphon pisum) forms multiple biotypes each of which is specialized to one or a few legume species. I hypothesize that effectors (saliva proteins) are one of the factors that are involved in host plant specialization of the pea aphid complex and initiated a research program to study the molecular mechanisms of plant-aphid interactions.