Identification of wheat blue dwarf phytoplasma effectors targeting plant proliferation and defence responses

Abstract

The identification of effectors from pathogenic microbes is one of the most important subjects for elucidating infection mechanisms. Wheat blue dwarf ( WBD ) phytoplasma causes dwarfism, witches' broom, and yellow leaf tips in wheat plants, resulting in severe yield loss in northwestern China. In this study, 37 candidate effector proteins were transiently expressed in Nicotiana benthamiana . Plants expressing the SAP 11‐like protein SWP 1 exhibited typical witches' broom. Interestingly, another protein, SWP 11, induced both cell death and defence responses, including H 2 O 2 accumulation and callose deposition. Analysis by qRT ‐ PCR was used to show that a marker gene of the hypersensitive response, HIN 1 , and three pathogenesis‐related genes, PR 1 , PR 2 and PR 3 , were significantly up‐regulated in leaves of N. benthamiana expressing SWP 11. In addition, SWP 12 and SWP 21 ( TENGU ‐like) were shown to suppress SWP 11‐, BAX ‐, and/or INF 1‐induced cell death. These results indicated that SWP 21 has a distinct role in virulence compared with TENGU and that WBD phytoplasma possesses effectors that target plant proliferation and defence responses. The ability of these effectors to trigger or suppress plant immunity provides new insights into the phytoplasma–plant interaction.