E6 - Phylogenetic Classification of Plant Pathogenic Mycoplasma-Like Organisms or Phytoplasmas

Abstract

This chapter presents a phytoplasma taxonomic scheme that is based on the analysis of two evolutionary markers: the 16S ribosomal ribonucleic acid (rRNA) gene and the spacer region that separates the 16S from the 23S rRNA genes. This chapter provides an outline of the procedures that are available for phylogenetically classifying an unknown phytoplasma strain. Information presented in this chapter includes phytoplasma phylogenetic relationships based on restriction fragment length polymorphisms (RFLP) analysis and sequence analysis of the 16/23S spacer regions. Phylogenetic analyses have provided a coherent framework for the classification of diverse taxa, including the Mollicutes. Another very attractive aspect of this type of analysis is the ability to analyze these phylogenetic markers from non-culturable prokaryotes, such as plant pathogenic mycoplasma-like organisms (MLOs). There are advantages and disadvantages associated with both RFLP and sequence analysis of rDNA for classifying phytoplasmas. RFLP analysis of the polymerase chain reaction (PCR)-amplified 16S rRNA gene is a rapid method to assess the potential affinity of an unknown phytoplasma.