, 1989; Yu et al., 1998; Berg et al., 1999; Blomquist et al., 2001; Barbara et al., 2002; Morton et al., 2003; Kakizawa et al., 2004, 2009). Furthermore, since they are major proteins of the phytoplasma cell surface, Imps are predicted to play some important roles in phytoplasma–host interactions. The formation of a complex between antigenic membrane protein (Amp) of onion yellows phytoplasma and insect microfilaments has been correlated with the phytoplasma-transmitting capability of leafhoppers, suggesting that the interaction between Amp and insect microfilaments plays a role in phytoplasma transmissibility

(Suzuki et al., 2006). Moreover, the Amp appears to have evolved under strong positive Quizartinib solubility dmso selection, indicating that it plays an important role in phytoplasma fitness (Kakizawa et al., 2006b, 2009). Genes encoding Imps have been isolated from several phytoplasma groups, and have been classified into three types: (1) the specific Imp found in sweet potato witches’ broom (Yu et al., 1998), apple proliferation (Berg et al., 1999), European stone fruit yellows (Morton et al., 2003), pear decline (Morton et al., 2003), and peach yellow leaf roll (Morton et al., 2003) phytoplasmas; (2) immunodominant membrane protein A (IdpA), found in western X-disease (WX) phytoplasma (Blomquist et al., 2001); and (3) Amp, found in aster yellows (Barbara et al.,

2002), clover phyllody (Barbara et al., 2002), and onion yellows (Kakizawa et al., 2004) phytoplasmas. These three types of proteins, Imp, IdpA, and Amp, share no amino acid sequence similarities FG-4592 datasheet and differ in their transmembrane structures. Several phytoplasma strains harbor genes encoding two types of these proteins and one of which is

predominantly expressed [e.g. OY and WX encode imp, in addition to each major protein gene (Kakizawa et al., 2006a, 2009)]. Imp is conserved in many phytoplasmas, and might thus represent the ancestral Imp (Kakizawa et al., 2009). PoiBI belongs to 16SrIII ribosomal group (Lee et al., 1998), which implies that the Imp of PoiBI might be IdpA, as it is in WX (Blomquist et al., 2001). Despite the commercial importance of PoiBI, its Imp has not been studied, and only a few of its genes have been cloned, second such as those encoding the 16S rRNA gene-ITS-23S ribosomal RNA (rRNA) gene region, isoleucine tRNA, ribosomal protein L15, L22, protein translocase (secY), and methionine aminopeptidase (Martini et al., 2007; Lee et al., 2010). In the present study, we cloned both the imp and idpA genes from PoiBI, and analyzed Imp and IdpA protein expression in PoiBI-infected poinsettia cultivars. Contrary to expectation, the major membrane protein of PoiBI is Imp, and not IdpA. Moreover, as part of a detailed analysis of the biology and diversity of PoiBI, we examined the evolutionary implications of the Imp and IdpA protein sequences.