Function and molecular mechanism analysis of Ca LasSDE460 effector involved in the pathogenesis of “ Candidatus Liberibacter asiaticus” in citrus

Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus ( Ca Las), is the most serious disease worldwide. Ca LasSDE460 was previously characterized as a potential virulence factor of Ca Las. However, the function and mechanism of Ca LasSDE460 involved in Ca Las against citrus is still elusive. Here, we showed that transgenic expression of Ca LasSDE460 in Wanjincheng oranges ( C. sinensis Osbeck) contributed to the early growth of Ca Las and the development of symptoms. When the temperature increased from 25 °C to 32 °C, Ca Las growth and symptom development in transgenic plants were slower than those in WT controls. RNA-seq analysis of transgenic plants showed that Ca LasSDE460 affected multiple biological processes. At 25 °C, transcription activities of the “Protein processing in endoplasmic reticulum” and “Cyanoamino acid metabolism” pathways increased while transcription activities of many pathways decreased at 32 °C. 124 and 53 genes, separately annotated to plant-pathogen interaction and MAPK signaling pathways, showed decreased expression at 32 °C, compared with these (38 for plant-pathogen interaction and 17 for MAPK signaling) at 25 °C. Several important genes (MAPKKK14, HSP70b, NCED3 and WRKY33), remarkably affected by Ca LasSDE460, were identified. Totally, our data suggested that Ca LasSDE460 participated in the pathogenesis of Ca Las through interfering transcription activities of citrus defense response and this interfering was temperature-dependent. Graphical Abstract