Submitted to: International Organization for Mycoplasmology
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2004
Publication Date: 7/11/2004
Citation: Lee, I., Zhao, Y., Bottner, K.D. 2004. Identification of insertion sequence (is)-like elements associated with aster yellows group phytoplasma strains. International Organization for Mycoplasmology. p. 65.
Technical Abstract: Novel insertion sequence (IS)-like elements were isolated and characterized from phytoplasma strains in the aster yellows (AY) group (16SrI). An analysis of a repetitive DNA sequence cloned from the genome of strain AY1, a member of subgroup 16SrI-B, revealed the presence of an open reading frame (ORF) that encodes a putative transposase (Tpase). Six IS-like elements were cloned from both strain AY1 and NJAY (a member of subgroup 16SrI-A). All six clones contained one ORF encoding a putative Tpase with 322 amino acids. In addition, the PCR assay using Tpase-specific primers revealed that 14 additional phytoplasma strains, representing 10 subgroups in the AY group and one subgroup in the Mexican periwinkle virescence group (16Sr XIII), also contain similar IS-like elements. All putative Tpases identified shared more than 80% amino acid or nucleotide sequence homology and have an identical DDE motif that is most similar to the DDE consensus of the Tpases of the IS3 family. The amino acid sequence of the Tpase shares a significant homology (an average of 36% identity and 55% similarity) with Tpases encoded by insertion sequences from several bacterial species of low G+C Gram-positive in the Firmicutes group. However, all IS-like elements identified lack apparent terminal inverted repeat (IR) sequences, another trait of the IS3 family. The novel IS-like elements associated with phytoplasmas in the AY and some other phytoplasma groups should represent a new IS family or at least a new subfamily within the IS3 family. Preliminary phytoplasma genomic DNA blot analyses using the putative IS as a probe revealed the presence of multiple copies of IS-like elements in each strain tested. The analysis also revealed that different symptom variants derived from the same parent phytoplasma strain exhibited different hybridization patterns. IS-mediated chromosomal recombination events may play a role in symptom expression/modulation in AY-diseased plants.