Stolbur and "bois noir" phytoplasma strains represent a distinct novel species, ‘Candidatus Phytoplasma solani'
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Data di Pubblicazione:
2013
Citazione:
Stolbur and "bois noir" phytoplasma strains represent a distinct novel species, ‘Candidatus Phytoplasma solani' / F. Quaglino, Y. Zhao, P. Casati, D. Bulgari, P.A. Bianco, W. Wei, R.E. Davis. ((Intervento presentato al 3. convegno European Bois Noir Workshop tenutosi a Barcelona nel 2013.
Abstract:
Phytoplasmas classified in group 16SrXII infect a wide range of plants and are transmitted by polyphagous planthoppers of the family Cixiidae (Lee et al., 2000). Based on 16S rRNA gene sequence identity and biological properties, group 16SrXII encompasses several species, including ‘Candidatus Phytoplasma australiense’, ‘Ca. Phytoplasma japonicum’, ‘Ca. Phytoplasma fragariae’ (IRPCM, 2004; Valiunas et al., 2006). Other group 16SrXII phytoplasma strains, associated with stolbur and bois noir diseases, have been informally proposed to represent a separate species, ‘Ca. Phytoplasma solani’, but a formal description of this taxon has not previously been published. In the present communication, on the basis of nucleotide sequence and phylogenetic analyses of multiple genes and assessment of biological properties, stolbur phytoplasma strains are described as representing a distinct species level lineage and novel taxon, ‘Ca. Phytoplasma solani’.
DNA fragments of the tuf, secY, and rplV-rpsC genes were PCR-amplified from strain STOL11 (STOL), originally from a diseased plant of Capsicum annuum in Serbia (Seemüller et al., 1994), which had been transmitted and maintained by grafting in plants of Madagascar periwinkle. Nucleotide sequences of 16S rRNA, tuf, secY, and rplV-rpsC genes from diverse group 16SrXII strains, and from reference strains of formally described ‘Ca. Phytoplasma’ species, were retrieved from the GenBank database, compiled in FASTA format, and aligned using BioEdit version 7.0.5. Phylogenetic analyses were done using the software MEGA4. Moreover, deduced amino acid sequences were aligned for phylogenetic analyses. Data on plant hosts, insect vectors, and geographic distribution of 16SrXII phytoplasmas were compared in order to determine whether stolbur and bois noir phytoplasmas formed an ecologically distinct population.
Our data provide evidence that ‘Ca. Phytoplasma solani’ strains clearly represent a distinct gene pool, based on 16S rDNA and variable gene sequence analyses, and occupy a distinct ecological niche.
According to IRPCM guidelines, phytoplasmas sharing >97.5% 16S rDNA nucleotide sequence similarity can be described as separate species if they are clearly distinguished by evident molecular diversity and ecological niche. Strain STOL11, selected as the potential 'Ca. Phytoplasma solani’ reference strain, shares 97.6% 16S rDNA sequence similarity with ‘Ca. Phytoplasma australiense’. We found that 'Ca. Phytoplasma solani’ intra-species sequence similarity was significantly and consistently greater (>99%) than inter-species similarity (<98.2% vs ‘Ca. Phytoplasma australiense’). Moreover, 16S rDNA sequence alignments identified a STOL11-unique signature sequence and two distinguishing sequence blocks (DSBs), whose combined use facilitates assignment of strains to the species. In previous work, 16S rDNA signature sequences have already been employed for separating biologically distinct ‘Ca. Phytoplasma’ species that shared >97.5% 16S rDNA sequence similarity (Seemüller et al., 2004). In our view, a strain of ‘Ca. Phytoplasma solani’ should (i) share >99% sequence similarity with a minimum of 1.2kb within the 16S rRNA gene of reference strain STOL11, and (ii) contain the identical STOL11-unique signature 16S rDNA sequence, and (iii) contain both DSBs of reference strain STOL11, with a tolerance of a single nucleotide difference in no more than one of the sequences. Strains that do not fulfill either criterion (ii) or criterion (iii) are considered ‘Ca. Phytoplasma solani’-related strains, even if they fulfill criterion (i).
Since additional genes were proposed for future delineation of species (Davis et al., 2012), further work was
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
F. Quaglino, Y. Zhao, P. Casati, D. Bulgari, P.A. Bianco, W. Wei, R.E. Davis
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