Identification Of A Conserved Phytoplasma Core Genome And Functional Characterization Of Imp From Wheat Blue Dwarf Phytoplasma

Wheat Blue dwarf phytoplasma(WBDp) disease is an important plant disease in the northwest region of China. It is transmitted by the leafhopper, Psammotettix striatus, in the field. The disease occurs in this region periodically and often causes significant economic damages. Because the phytoplasma can not be cultured up to date, there are large amounts of limitations on phytoplasma researches. With the rapid development of highthrough-output sequencing technology, several phytoplasma genomes have been completed. Based on these data, functional genomics is blooming. Although three effectors from the phytoplasma have been further identified, the research in this area needs to be further explored. This study uses comparative genomics to analyze the available phytoplasma genomes and mine the conserved phytoplasma core genome. It is expected to find some differences in the potential secreted proteins among different 16 S r groups. At the same time, the function of Immunodominant membrane protein(Imp) was primarily characterized. This research will put new ideas about phytoplasma genome assembly and the study of functional genomics.The BioLinux platform was used to perform comparative genomics with 10 different phytoplasma strains from 5 different 16 Sr groups. The result showed this core genome contained 170 conserved genes among these 10 phytoplasma genomes. Interestingly, the core genome lacks potential secreted proteins, indicating that the effectors in the different 16 Sr groups were diverse and the pathogenic mechanisms may be different. In the core genome, the genes encoding the proteins of translation, transcription, biogenesis et al. account for the largest proportion. In addition, a strict strategy was used to identify group specific genes. The result indicated that most of genes are hypothetical genes, but some are potential effectors, which also means that the pathogenic mechanisms among different 16 Sr groups are different. Amp and Imp have a common origin, but Amp in 16 Sr XII group and Imp in 16 Sr III group were identified in the group specific gene pool, which showed that these two genes evolved faster. Previously it has been reported that Amp are under the positive selection. Usually genes under positive selection have important functions such as immunity, defense et al.Based on the above results, we started to characterize the function of Imp from Wheat Blue Dwarf phytoplasma. After BLAST analysis, only one copy of Imp was found in the WBDp genome. The phylogenetic tree using the maximum likelihood method showed that Imp from WBDp can be clustered in the branch of Imp. And from this tree it is easly found that only 16 Sr XII and 16 Sr I group contain Amp genes. All 16 Sr groups used in this tree include Imp genes. For the analysis of Amp and Imp genome location, Imp have two locations but the location of Amp is stable. Besides, we cloned Imp of WBDp and made the polyantibody, which can be used for specific detection of WBDp. Finally, two methods were used to prove that Imp of WBDp interacts with actin of the host vector. This result layed foundation to study phytoplasma transmission mechanism.