Abstract:

【Objective】 This study was conducted to investigate the molecular variability of the coat protein (CP) gene of Citrus tatter leaf virus (CTLV) isolates collected from China. 【Method】 The CP gene of 18 CTLV isolates from different geographical origins and citrus varieties were amplified by reverse transcription-polymerase chain reaction (RT-PCR). The DNA products were cloned and sequenced, and sequence analysis was conducted by DNAMAN. 【Result】 The CP gene of 18 CTLV isolates were all 714 nucleotides in length, and the putative CP contained 237 amino acids (aa). The identities of nucleotide and deduced amino acid sequences of CP gene among 18 isolates ranged from 88.5% to 99.9% and 91.1% to 99.6%, respectively. Corresponding to the mutation G289→A or C, A409→C, and G414→T on nucleotide sequences of CP gene, amino acids at positions 97, 137, and 138 of CP were different between isolates expressing mild symptoms and isolates expressing severe symptoms in the indicators. Q97 or K97, Q137, H138 were discovered in most mild isolates, whereas E97, R137 or K137, Q138 were shared by most severe isolates. Phylogenetic trees based on the aa sequences of the coat proteins showed that 18 CTLV isolates were divided into two clusters, and most of the mild isolates (4/6) belonged to theⅠgroup and most severe isolates (10/12) belonged to theⅡgroup. 【Conclusion】 The CP gene of CTLV was relatively conserved. The differences between mild and severe strains are very subtle, with three nucleotide positions (289, 409 and 414) appearing to determine the pathogenicity of virus.

Key words: Citrus tatter leaf virus, CP gene, cloning, sequencing