title: Folate biosynthesis pseudogenes, PsifolP and PsifolK, and an O-sialoglycoprotein endopeptidase gene homolog in the phytoplasma genome.
abstract: Phytoplasmas are wall-less phytopathogenic prokaryotes of small genome sizes that are obligate parasites of insect vectors and plant hosts. We have cloned a clover phyllody (CPh) phytoplasma DNA locus containing five potential coding sequences. Two were identified as pseudogenes (PsifolP and PsifolK) homologous to folP and folK genes, which encode dihydropteroate synthase (DHPS) and 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK), respectively, in other bacteria. Evolution of the phytoplasma presumably involved loss of functions through the formation of these and other pseudogenes during adaptation to obligate parasitism. The findings suggest that the phytoplasma lacks capacity for de novo folate biosynthesis and possesses a transport system for absorption of preformed folate from host cells. The PsifolP-PsifolK region was flanked by three open reading frames (ORFs) encoding a DegV family protein, a hypothetical protein with a P60-like lipoprotein domain homologous with the P60-like Mycoplasma hominis protein, and a glycoprotease (Gcp) protein that possibly functions as a host adaptation or virulence factor.
authors.affiliation: Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Room 118, Building 004, BARC West, 10300 Baltimore Avenue, Beltsville, MD 20705, USA. davisr@ba.ars.usda.gov
authors.forename: Robert E
authors.initials: RE
authors.lastname: Davis
authors.forename: Rasa
authors.initials: R
authors.lastname: Jomantiene
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Ellen L
authors.initials: EL
authors.lastname: Dally
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D005492:Folic Acid / Q000096:biosynthesis* / Q000235:genetics*; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D008666:Metalloendopeptidases / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010802:Phylogeny; D045582:Phytoplasma / Q000235:genetics* / Q000378:metabolism*; D011544:Pseudogenes; D017386:Sequence Homology, Amino Acid
chemical_list: D004269:DNA, Bacterial; D005492:Folic Acid; D008666:Metalloendopeptidases; C070738:O-sialoglycoprotein endopeptidase