Abstract
BackgroundPhytoplasmas are bacteria without cell walls from the class Mollicutes. They are obligate intracellular plant pathogens which cause diseases in hundreds of economically important plants including the grapevine (Vitis vinifera). Knowledge of their biology and the mechanisms of their interactions with hosts is largely unknown because they are uncultivable and experimentally inaccessible in their hosts. We detail here the global transcriptional profiling in grapevine responses to phytoplasmas. The gene expression patterns were followed in leaf midribs of grapevine cv. 'Chardonnay' naturally infected with a phytoplasma from the stolbur group 16SrXII-A, which is associated with the grapevine yellows disease 'Bois noir'.ResultsWe established an on field experimental system in a productive vineyard that allowed application of molecular tools in a plant natural environment. Global transcription profiles of infected samples were compared with the healthy ones using microarray datasets and metabolic pathway analysis software (MapMan). The two-year-long experiment revealed that plant genes involved in primary and secondary metabolic pathways were changed in response to infection and that these changes might support phytoplasma nutrition. A hypothesis that phytoplasmas interact with the plant carbohydrate metabolism was proven and some possibilities how the products of this pathway might be utilized by phytoplasmas are discussed. In addition, several photosynthetic genes were largely down-regulated in infected plants, whereas defense genes from the metabolic pathway leading to formation of flavonoids and some PR proteins were significantly induced. Few other genes involved in defense-signaling were differentially expressed in healthy and infected plants. A set of 17 selected genes from several differentially expressed pathways was additionally analyzed with quantitative real-time PCR and confirmed to be suitable for a reliable classification of infected plants and for the characterization of susceptibility features in the field conditions.ConclusionThis study revealed some fundamental aspects of grapevine interactions with the stolbur 'Bois noir' phytoplasma in particular and some plant interactions with phytoplasmas in general. In addition, the results of the study will likely have an impact on grape improvement by yielding marker genes that can be used in new diagnostic assays for phytoplasmas or by identifying candidate genes that contribute to the improved properties of grape.
Highlights
Phytoplasmas are bacteria without cell walls from the class Mollicutes
In order to demonstrate the potential of grapevine plants infected with 'Bois noir' (BN)' phytoplasma to interact with their pathogen, we present here the qualitative and quantitative changes in the global gene expression profiles of the healthy and infected plants of cv
In none of them 'BN' phytoplasma was detected by the quantitative real-time PCR reactions (qRTPCR)
Summary
Phytoplasmas are bacteria without cell walls from the class Mollicutes. They are obligate intracellular plant pathogens which cause diseases in hundreds of economically important plants including the grapevine (Vitis vinifera). Phytoplasmas are plant pathogenic bacteria belonging to the class Mollicutes [1]. They are cell wall-free, and both their cell size (0.1-0.8 μm in diameter) and genome size (0.5-1.3 Mbp) are the smallest among bacteria. They are transmitted from plant to plant by sap-feeding insect vectors and they propagate within the cytoplasm of both insects and plants. For them the practice of naming a phytoplasma on the basis of the associated plant syndrome is still valid [3]
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