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Transient Expression of Candidatus Liberibacter Asiaticus Effector Induces Cell Death in Nicotiana benthamiana

Marco Pitino, Cheryl M. Armstrong, Liliana M. Cano, Yongping Duan
Frontiers in plant science 2016 v.7 no.982 pp. -
Candidatus Liberibacter asiaticus, Citrus, Nicotiana benthamiana, bioinformatics, cell death, chloroplasts, genome, genomics, greening disease, heterologous gene expression, immunity, microscopy, pathogen-associated molecular patterns, plant pathogenic bacteria, proteins
Candidatus Liberibacter asiaticus (Las) is a phloem-limited bacterial plant pathogen, and the most prevalent species of Liberibacter associated with citrus huanglongbing (HLB), a devastating disease of citrus worldwide. Although the complete sequence of the Las genome provides the basis for studying functional genomics of Las and molecular mechanisms of Las-plant interactions, the functional characterization of Las effectors remains a slow process since Las has a significantly reduced genome and remains to be cultured. Like other plant pathogens, Las may deliver effector proteins that modulate a variety of host cellular functions during the infection progress. In this study, we identified 16 candidate Las effectors via bioinformatics, and transiently expressed them in Nicotiana benthamiana plants. Using this heterologous expression system, diverse subcellular localization patterns with different shapes and aggregates of the effector candidates were revealed by UV- microscopy. Intriguingly, one of the sixteen candidates, Las5315, was found to localize to the chloroplasts and induced cell death at 3 days post inoculation in N. benthamiana. Moreover, Las5315 also suppressed pathogen-associated molecular patterns (PAMP)-triggered immunity (PTI) induced by Xcc-flg22. Overall, this study provides new insight into the localization and potential roles of these Las effectors in planta.