Characterization of four vital protein encoding genes of Candidatus Liberibacter asiaticus the causal agent of citrus greening disease

Abstract

Candidatus Liberibacter asiaticus (Ca. L. asiaticus), a gram negative, phloem-limited, and unculturable bacteria is the causal agent of citrus greening disease. The disease is considered as one of the most serious threats to the citrus industry worldwide. It is responsible for heavy crop losses irrespective of citrus cultivar or rootstock used. During the infection process, the bacterium produces several pathogenesis-related proteins that are crucial for its survival and multiplication in plant phloem tissue and saliva of its insect vectors citrus psylla, inside which it multiplies efficiently. There is a tremendous potential of developing antimicrobial inhibitors against these proteins to reduce pathogen population in plant phloem tissue and in insect vectors as potential tool in disease management strategy. In the present study, we sequenced and characterized four crucial protein genes from 18 samples across India. The four protein genes includes two component response regulator protein, periplasmic solute binding protein, putative protease IV transmembrane protein and serine protease do-like protein of the causal bacterium. Secondary and tertiary structures of the proteins were also predicted using PSIPRED and TMHMM software, respectively. Phylogenetic analyses and secondary protein structure prediction reveals that these four proteins are unique, essential and conserved in Ca. L. asiaticus populations infecting different citrus cultivars prevalent in India. Further, these structures gave an idea about active sites which can act as perfect target sites for blocking. These bacterial encoded proteins are potential targets of antimicrobial inhibitors.