Abstract:

【Objective】 The objective of this study was to investigate the TTSS in Erwinia amylovora and the HrpA selection pressure in Erwinia spp. 【Method】 Bioinformatics strategies were used in this study by BLAST scan to search the Erwinia amylovora genomic nucleotide database and compare their homology, and analyze the selection pressure about the surface protein HrpA which is associated with the interaction between Erwinia spp. and the hosts. 【Result】 Twenty-seven TTSS- like proteins were identified in the 40 kb pathogenecity island. In contrast, the selection pressure value for HrpA was strongly elevated by comparison with those of housekeeping genes and HrpN. The comparison among multi HrpA sequences showed that most of the HrpA N terminus were subjected to positive selection and the C terminus were subjected to purifying selection. Erwinia spp. phylogenetic tree based on HrpA showed that there were two distinct groups. Analysis indicated that different modes of selection operated after separation of species. 【Conclusion】 The TTSS in Erwinia amylovora lies between 3.14 Mb to 3.18 Mb and the pathogen uses this system to invade the host. At the bacterial cell surface, the TTSS has a filamentous-like structure, HrpA, which serves as a conduit for the transfer of effectors into the plant cell. HrpA has a strong selection pressure in its evolutionary history. This paper has some positive significance in revealing the host range and plant resistance.

Key words: Erwinia amylovora, TTSS, HrpA, positive selection, purifying selection