, 2001), amino acid substitutions in WX IdpA should affect the properties of the WX cell surface and subsequently increase the evolutionary fitness of WX. These results suggest that IdpA has an important role in host–phytoplasma interactions, particularly in WX. PFT�� mw Further sequence comparisons of Imp or IdpA among several strains of WX would reveal the functional importance of Imps in 16SrIII ribosomal group phytoplasmas. Most of the 30 poinsettia cultivars examined in this study

were infected with PoiBI, as shown by PCR amplification of the phytoplasma 16S rRNA gene, but phytoplasma infection could not be detected in four of the cultivars: ‘Flaming Sphere’, ‘Annette Hegg Marble’, ‘Annette Hegg Diva’, and ‘Eckespoint C-1 Red’. ‘Eckespoint C-1 Red’ was previously reported to be phytoplasma-free, along with ‘Eckespoint C-1 White’ (Dole & Wilkins, 1991), in agreement with our results. However, we cannot exclude the possibility that PCR failures resulted in false negatives for some or all of these cultivars. PCR failures could have arisen if the level of PoiBI accumulation was very low, perhaps as a result of the particular cultivar characteristics, growth stage, or growth conditions, or if the cultivar(s) contained PCR inhibitory compounds. Alternatively, the possibility of the sequence variability in the PCR primer

binding region cannot be excluded. It is possible that nested-PCR using 16SrIII group-specific primers, instead of the single PCR using the primers in this study, might yield amplification products. However, we extracted the template DNA for all samples from the poinsettia leaf midribs, where the concentration of phytoplasma cells http://www.selleckchem.com/products/Roscovitine.html is

expected to be high, and we followed the same extraction Interleukin-2 receptor protocol for all poinsettia cultivars. To eliminate the influence of PCR inhibitory compounds, we used DNA diluted by tenth and hundredth as a template for PCR amplification. However, we could not yield fragments from all of four cultivars (data not shown). Moreover, phenotypically, these four cultivars are taller and had less branching than PoiBI-infected poinsettias (Fig. S2). These features were similar to those of the healthy poinsettia. Therefore, we conclude that in addition to ‘Eckespoint C-1 Red’ and ‘Eckespoint C-1 White’, several other commercially available poinsettias, that is, ‘Flaming Sphere’, ‘Annette Hegg Marble’, and ‘Annette Hegg Diva’, are free of phytoplasma infection. The conservation of Imp sequences among many groups of phytoplasmas has led to the suggestion that Imp represents an ancestral type of Imp (Kakizawa et al., 2009). This proposal suggests that PoiBI has retained Imp as its major membrane protein, and that the expression level of IdpA had increased during the evolution of WX, causing IdpA to become the Imp of WX. It is known that WX is transmitted predominantly by Colladonus montanus (Kirkpatrick et al., 1987), whereas it has been assumed that PoiBI is transmitted only by grafting.