日日春葉片黃化病植物菌質體核醣體 RNA, rplV-rpsC, secY 與 tuf 基因之譜系分析

Abstract

A new disease named as periwinkle leaf yellowing (PLY) was first observed in a flower production farm in Dayuan Township (Taoyuan county, Taiwan) in August 2005. Sequence analysis of 16S rDNA, 16S-23S rDNA ISR, and partial 23S rDNA sequence revealed that the causative agent of PLY was closely related to the phytoplasmas of the aster yellows (AY) group (16SrI group) which cause diseases in many horticultural and vegetable crops worldwide, and can be delineated into 10 subgroups. Six cultivated plants including periwinkle plant, chrysanthemum, cosmos, torenia, Persian violet, goosegrass and cucumber, were determined to be the host plants of PLY phytolasma. Monthly PCR detection indicated that PLY phytoplasma was detected in host plants from June to October in 2007, and from July to October in 2007. However, it can be detected earlier since April in 2009. To further clarify the phylogenetic relationship of strain PLY among 16SrI phytoplasmas, six phylogenetic trees were constructed in this study. Beside the phylogenetic trees based on the independent analysis of 16S rRNA, rplV-rpsC, secY and tuf gene sequences, two other trees based on the analysis of the comprising gene sequence of 16S rRNA, rplV-rpsC and secY, and the comprising gene sequence of rplV-rpsC and secY were also constructed. The results indicate that the strain PLY was closely related to 16SrI-B and 16SrI-D subgroup, and could be a new subgroup based on the phylogenetic tree constructed by rplV-rpsC gene sequences. In addition, the phylogenetic analysis of the comprised gene sequences showed similar tree topology when compared with sequence analysis of the rplV/ rpsC gene or of the secY gene alone. The main difference is that the branch lengths were elongated in the comprised gene tree. To further confirm the subgroup affiliation of PLY phytoplasma, the 16S rRNA gene sequences of 10 closely related phytoplasma strains were digested in silico, and the similarity coefficients were then calculated. The results also support the conclusion that PLY phytoplasma might belongs to a new 16SrI subgroup. The putative restriction site analysis can also distinguish PLY phytoplasma from other close related phytoplasma strains in phylogenetic analysis.