Shotgun proteomic analysis of mulberry dwarf phytoplasma

MD phytoplasmas, which belong to the 16SrI-B subgroup based on the 16S DNA analysis, were purified from infected tissues using a combination of differential centrifugation and density gradient centrifugation. The expressed proteome of phytoplasma was surveyed by one-dimensional SDS-PAGE and nanocapillary liquid chromatography-tandem mass spectrometry. A total of 209 phytoplasma proteins were unambiguously assigned, including the proteins with the functions of amino acid biosynthesis, cell envelope, cellular processes, energy metabolism, nucleosides and nucleotide metabolism, replication, transcription, translation, transport and binding as well as the proteins with other functions. In addition to these known function proteins, 63 proteins were annotated as hypothetical or conserved hypothetical proteins.Taken together, a total of 209 phytoplasma proteins have been experimentally verified, representing the most extensive survey of any phytoplasma proteome to date. This study provided a valuable dataset of phytoplasma proteins, and a better understanding of the energy metabolism and virulence mechanisms of MD phytoplasma.The mulberry tree, whose leaves are the chief food for mulberry silkworm (Bombyx mori L.), is a perennial woody plant of considerable economic importance and has long been cultivated for sericulture. Mulberry trees are often affected by a number of diseases prevalent throughout their life cycles in different agroclimatic zones. Among all the diseases, mulberry dwarf (MD) is one of the most serious infectious diseases [1]. The causal pathogen of this disease, MD phytoplasma, was observed in the sieve tubes of plants affected for the first time in 1967 [2]. Phytoplasmas infect several hundred plant species worldwide, representing about 100 families including ornamental plants and many important crops [3]. They are morphologically and ultrastructurally resembled animal mycoplasmas [4], which are cell-wall-less prokaryotes in the class Mollicutes [5]. Due