The flagella of ‘Candidatus Liberibacter asiaticus’ and its movement in planta

摘要

Citrus huanglongbing (HLB) is the most devastating citrus disease worldwide. ‘ Liberibacter asiaticus’ (Las) is the most prevalent HLB causal agent that is yet to be cultured. Here, we analysed the flagellar genes of Las and and observed two characteristics unique to the flagellar proteins of Las: (i) a shorter primary structure of the rod capping protein FlgJ than other bacteria and (ii) Las contains only one flagellin‐encoding gene (CLIBASIA_02090), whereas other species carry at least three flagellin‐encoding genes. Only but not restored the swimming motility of mutant. Pull‐down assays demonstrated that FlgJ interacts with FlgB but not with FliE. Ectopic expression of in mutants restored the swimming motility of ∆ mutant and ∆ mutant, but not that of the null mutant ∆ . No flagellum was observed for Las in citrus and dodder. The expression of flagellar genes was higher in psyllids than . In addition, western blotting using flagellin‐specific antibody indicates that Las expresses flagellin protein in psyllids, but not . The flagellar features of Las suggest that Las movement in the phloem is not mediated by flagella. We also characterized the movement of Las after psyllid transmission into young flush. Our data support a model that Las remains inside young flush after psyllid transmission and before the flush matures. The delayed movement of Las out of young flush after psyllid transmission provides opportunities for targeted treatment of young flush for HLB control.