|ZHOU, LIJUAN - University Of Florida|
|POWELL, CHARLES - University Of Florida|
|LI, WENBIN - Animal And Plant Health Inspection Service (APHIS)|
|IREY, MIKE - Us Sugar Corporation|
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2013
Publication Date: 12/13/2013
Citation: Zhou, L., Powell, C.A., Li, W., Irey, M., Duan, Y. 2013. Prophage-mediated dynamics of ‘Candidatus Liberibacter asiaticus’ populations, the destructive bacterial pathogens of Citrus Huanglongbing. PLoS One. 8(12):e82248. doi:10.1371/journal.pone.0082248.
Interpretive Summary: “Candidatus Liberibacter asiaticus” (Las) is one of the three Liberibacter species associated with citrus Huanglongbing (HLB), a newly emerging and century-old devastating disease of citrus worldwide. In this study, we investigated two other highly diversified regions of Las prophages and revealed the prophage/phage-mediated population dynamics of Las in plant and insect hosts, and their correlation with disease symptoms. There were nine different types of Las population based on two hyper-variable regions of Las prophages/phages. Among them, Types A and B share highly conserved sequences and localize in the two prophages, FP1 and FP2, respectively. Type A population was much more abundant in the Las-infected psyllid than the Las-infected host plants. Type A, B, C and D are the four abundant types in Las-infected citrus and periwinkle. However, only three, Type A, B and C are abundant types in Las-infected psyllids. Intriguingly, the Type D was not present in the psyllilds, but was associated with blotchy mottle symptom. These results indicated the prophages/phages are the driving force for the genetic diversity of Las, and the Las bacterial population dynamics are different in different plant and insect hosts. These finding are important for epidemiology and development of new control strategies of citrus HLB.
Technical Abstract: Prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. There are at least two prophages in the chromosomes of Floridian ‘Candidatus Liberibacter asiaticus’ (Las) isolates. In this study, seven additional types of variants were identified from two hyper-variable regions. Among them, Types A and B share highly conserved sequences and localize in the two prophages, FP1 and FP2, respectively. Although Types A, B and C are all more abundant in our three libraries from Las-infected psyllid, citrus and periwinkle, Type A was much more abundant in the Las-infected psyllid than the Las-infected host plants. Sequence analysis of these variants revealed that the variations might result from recombination and reassortment. Conventional PCR results using type-specific primers indicated that A, B, C and D are the four abundant types in Las-infected citrus and periwinkle. However, only A, B and C are abundant types in Las-infected psyllids. Typing result for Las-infected citrus field samples indicate that only the Type D population was directly associated with huanglongbing (HLB) symptoms. Extended sequencing of the Type D region revealed a potential third prophage/phage in the Las genome. Dramatic variations in these prophage regions were also found among the global Las isolates. These results first demonstrate prophage/phage-mediated population dynamics in plant and insect hosts, and their correlation with disease symptoms. The methods for detection and differentiation of Las populations are also exemplified here.