|PUTTAMUK, THAMRONGJET - Kasetsart University|
|ZHOU, LIJUAN - University Of Florida|
|THAVEECHAI, NIPHONE - Kasetsart University|
|ZHANG, SHOUAN - University Of Florida|
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2014
Publication Date: 12/1/2014
Citation: Puttamuk, T., Zhou, L., Thaveechai, N., Zhang, S., Armstrong, C.M., Duan, Y. 2014. Genetic diversity of Candidatus Liberibacter asiaticus based on two hypervariable effector genes in Thailand. PLoS One. 9(12):e112968. doi: 10.1371/journal.pone.0112968.
Interpretive Summary: Huanglongbing (HLB), also known as citrus greening, is a very widespread and destructive disease of citrus. It is associated with ‘Candidatus Liberibacter asiaticus’ (Las), a phloem-restricted alphabacterium. In an effort to better understand the bacterium and its spread, investigations into the genetic diversity and the population dynamics of Las isolates from Thailand were performed using the two hypervariable-effector genes, lasAI and lasAII, which locate in the Las prophage FP1 and FP2, respectively. Overall, 239 infected citrus and 55 infected psyllid samples collected from different provinces throughout Thailand were examined, resulting in the PCR amplification of the hypervariable genes from 92% of the samples with 48.29% containing lasAI, 63.26% containing lasAII, and 19.38% containing both lasAI and lasAII. Sequence analyses of these two hypervariable genes showed that extensive variation exists within the full and partial repeat sequence of lasAI compared to lasAII. This study revealed that Las isolates from HLB-affected psyllids contained FP1 more frequently, with 96.36% containing FP1 and 29.09% FP2, although the opposite was true of HLB-affected citrus plants, with 37.23% containing FP1 and 71.12% containing FP2. These results indicate the prophage dynamics of Las bacteria were signifcantly different between insect and plant hosts. In addition, the phylogenetic analysis of the two hypervariable effector genes in this study grouped the Las Thai isolates with isolates from both China and the Philippines, suggesting introductions of Las into Thailand from both of these areas.
Technical Abstract: Huanglongbing (HLB), also known as citrus greening, is one of the most destructive diseases of citrus worldwide. HLB is associated with three species of ‘Candidatus Liberibacter’ with ‘Ca. L. asiaticus’ (Las) being the most widely distributed around the world, and the only species detected in Thailand. To understand the genetic diversity of Las bacteria in Thailand, we evaluated two closely-related effector genes, lasAI and lasAII, found within the Las prophages from 239 infected citrus and 55 infected psyllid samples collected from different provinces in Thailand. The results indicated that most of the Las-infected samples collected from Thailand contained at least one prophage sequence with 48.29% containing prophage 1 (FP1), 63.26% containing prophage 2 (FP2), and 19.38% containing both prophages. Interestingly, FP2 was found to be the predominant population in Las-infected citrus samples while Las-infected psyllids contained primarily FP1. The multiple banding patterns that resulted from amplification of lasAI imply extensive variation exists within the full and partial repeat sequence while the single band from lasAII indicates a low amount of variation within the repeat sequence. Phylogenetic analysis of Las-infected samples from 22 provinces in Thailand suggested that the bacterial pathogen has been introduced to Thailand from China and the Philippines. This is the first report evaluating the genetic variation of a large population of Ca. L. asiaticus infected samples in Thailand using the two effector genes from Las prophage regions.