A Witches' Broom Phytoplasma effector induces stunting by stabilizing a bHLH transcription factor in plants
O_LIPhytoplasmas are specialized phloem-limited bacteria that cause diseases on various crops resulting in significant agricultural losses. This research focuses on the jujube Witches Broom (JWB) phytoplasma and investigates the host-manipulating activity of the effector SJP39. C_LIO_LIWe found that SJP39 directly interacts with the plant transcription factor bHLH87 in the nuclei. SJP39 stabilizes the bHLH87 homologs in A. thaliana and jujube, leading to growth defects in the plants. C_LIO_LITranscriptomic analysis indicates that SJP39 affects the gibberellin (GA) pathway in jujube. We further demonstrate that ZjbHLH87 regulates GA signalling as a negative regulator and SJP39 enhances this regulation. C_LIO_LIThe research offers important insights into the pathogenesis of JWB disease and identified SJP39 as a virulence factor that can contribute to the growth defects caused by JWB phytoplasma infection. These findings open new opportunities to manage JWB and other phytoplasma diseases. C_LI