Application of laser microdissection to study phytoplasma site-specific gene expression in the model plant Arabidopsis thaliana.

Many aspects of plant diseases caused by phytoplasmas are still unknown, as these pathogens are phloem restricted, uncultivable wall-less bacteria and must be studied always in association with their host. Phytoplasma transcripts are strongly underrepresented within host tissues and this poses problems for gene expression analyses. In this study, a procedure was established to infect the model plant Arabidopsis thaliana with the phytoplasma Flavescence dorée, a serious threat to European viticulture. Rates of phytoplasma infective insects and transmission efficiency to A. thaliana as well as pathogen loads were measured in different tissues of infected A. thaliana plants, and modification of phloem cell ultrastructure was observed in infected plant tissues at microscopic level. Moreover, a protocol for the application of laser microdissection to analyze plant and phytoplasma gene expression profiles in the specific colonized tissue was designed. The procedure allowed a good preservation of the plant tissue anatomy. Results showed that the extracted RNA was suitable for qualitative and quantitative RT-PCR, since both plant and pathogen transcripts, either abundant or rare ones, could be detected without any pre-amplification step. The combined use of laser microdissection approach and A. thaliana to study phytoplasmas opens the way to exploit biological, molecular and bioinformatic tools available for the model plant and to elucidate key pathways of the infection mechanisms of these important plant pathogen.