Molecular Identification and Related Gene Sequence Analysis of Phytoplasma of Gendarussa vulgaris Witches’-broom in Yunnan Province

Purpose To determine whether the pathogen of Gendarusssa vulgaris Nees collected from the Yuanmou area infection with witches’-broom disease was phytoplasma.

Method The 16S rRNA, rp and secY gene were amplification, cloning and sequencing analysis by using universal or semi-universal specific primers of phytoplasmas 16S groups and subgroups. In addition, we also analyzed and predicted the protein characteristics and structure of secY protein.

Results In this study, we obtained the 16S rRNA gene (by nested PCR) with gene fragments of 1 248 bp, the rp gene of 1 171 bp, and the secY gene of 1 425 bp. The rp and secY gene-based phylogenetic trees and nucleotide sequences homology alignment were congruent with that inferred from the 16S rRNA gene. They were closely related to the genetic evolutionary relationship of 16S rII-A subgroup phytoplasma strains. But the rp gene and secY gene sequences could exhibit greater variables of genetic variation than the 16S rRNA gene sequence. In addition, bioinformatics analysis and preliminary discussion on secY protein were carried out. We found that it had 10 obvious and relatively uniformly distributed transmembrane spiral regions without signal peptide.

Conclusion Gendarussa vulgaris witches’-broom phytoplasma disease occurs due to infection by phytoplasma pathogens. This phytoplasma strain was divided into 16S rII-A subgroup, and its related candidate species was Candidatus phytoplasma aurantifolia. By analyzing the biological information of the secY protein, it was found that exists in the form of a hydrophobic stable transmembrane protein in the susceptible Gendarussa vulgaris plant. It contains 10 obvious hydrophobic transmembrane regions, and it has no signal peptide.