Skip to main content
ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #297139

Title: Induction of innate immune responses by flagellin from the intracellular bacterium, ‘Candidatus Liberibacter solanacearum’

item Hao, Guixia
item Pitino, Marco
item DING, FANG - University Of Florida
item Lin, Hong
item Stover, Eddie
item Duan, Ping

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2014
Publication Date: 8/5/2014
Citation: Hao, G., Pitino, M., Ding, F., Lin, H., Stover, E.W., Duan, Y. 2014. Induction of innate immune responses by flagellin from the intracellular bacterium, ‘Candidatus Liberibacter solanacearum’. Biomed Central (BMC) Plant Biology. 14:211.

Interpretive Summary: Zebra chip (ZC) is an important potato disease causing millions of dollars in losses to both potato producers and processors in the United States. This disease is caused by ‘Candidatus Liberibacter solanacearum’ (Lso) and transmitted by the potato psyllid, Bactericera cockerelli. So far all commercial potato cultivars appear to be susceptible to ZC disease and the only strategy for controlling the spread of the disease is to control the potato psyllids. We found that Lso encodes a flagellin protein that contains the conserved flg22 domain. We examined the pathogen-associated molecular patterns (PAMP) activity of Lso flagellin and its flg22 peptide, and determined the gene expression induction associated with the PAMP-triggered immunity (PTI). We showed that the full length flagellin gene induces a much stronger PTI response compared to its peptide alone. The ability of the bacterial plant pathogen flagellins to be perceived by the plant recognition receptors and trigger the defense responses may provide a control strategy for zebra chip disease through flagellin / receptor interactions.

Technical Abstract: Candidatus Liberibacter solanacearum (Lso) is a phloem-limited alphaproteobacterium associated with the devastating zebra chip disease of potato. Like other members of Liberibacter, Lso-ZC1 encodes a flagellin domain-containing protein (FlaLso,) with a conserved 22 amino-acid domain (flg22Lso). To understand the innate immune responses triggered by this unculturable intracellular bacterium, we studied the pathogen-associated molecular patterns (PAMPs) triggered immunity in a non-host plant, Nicotiana benthamiana, using the flg22Lso peptide and the full length flaLso gene. Our results showed that the expression of flaLso via Agrobacterium-mediated transient expression induced a slow cell death in the inoculated leaves of N. benthamiana, which was coupled with a burst of reactive oxygen species (ROS) production. Moreover, the expression of several representative genes involved in innate immunity was transiently up-regulated by the flg22Lso and flaLso in N. benthamiana. The flaLso, however, induced stronger up-regulations, especially that of FLS2 and RboH in N. benthamiana. Although neither cell death nor ROS were induced by the synthetic flg22Lso, weak callose deposition was observed in infiltrated leaves of tobacco, tomato, and potato plants. These results revealed that in order to avoid detection during its intracellular life cycle, the Lso bacterium not only lacks avirulence proteins but has also evolved to only weakly activate PAMP triggered immunity.