Phytopathogenic Prokaryotes Research Articles

A Xanthomonas oryzae type III effector XopL causes cell death through mediating ferredoxin degradation in Nicotiana benthamiana

Plant pathogenic bacteria engage in an ongoing struggle for survival. Gram negative phytopathogenic prokaryotes deploy type III secretion system to deliver effector proteins into plant cells to manipulate the host cellular environment. In many cases, the targets of these effector proteins are unknown. The bacterial blight pathogen, Xanthomonas oryzae pv. oryzae (Xoo), causes a devastating disease in rice and the Xoo-rice interaction is an example of the ongoing evolutionary battle between plants and pathogens. In this study, we show that an effector XopL from Xoo exhibits E3 ubiquitin ligase activity and induces cell death in the nonhost Nicotiana benthamiana (Nb). Through yeast two-hybrid, co-immunoprecipitation, and biomolecular fluorescence complementation assays, it was shown that XopL interacts with ferredoxin (NbFd), an electron transport molecule in plant chloroplasts. XopL induced defense-related response in Nb and specifically targeted NbFd for ubiquitination and ubiquitin-mediated degradation, a process that increased the production of reactive oxygen species (ROS). This study demonstrates the ubiquitination and degradation of NbFd as a result of XopL activity, which further illustrates the tremendous functional diversity in Xanthomonas effector proteins.

Comparative genomics in phytopathogenic prokaryotes reveals the higher relative abundance and density of long-SSRs in the smallest prokaryotic genome.

Frequency and distribution of long-SSRs were studied in 18 phytopathogenic prokaryotes. Higher relative abundance of the long-SSRs was observed in phytopathogenic prokaryotes when compared to non-pathogenic control. The frequency of these SSRs was positively correlated with size and GC content of the genomes of phytopathogenic prokaryotes. Interestingly, phytopathogens with higher GC content in the genome were found to posses longer repeat motifs of SSRs, whereas those having lesser GC content were harbouring shorter repeat motifs. Higher abundance of tri- and hexa-nucleotide repeat motifs were the characteristic of actinomycetes, where as higher abundance of mono- and tetra-nucleotide repeats were the characteristic of the mollicutes. The maximum relative abundance and relative density of SSR were found in the smallest genome of host-adapted pathogen Aster yellow, however, length of microsatellite repeat units was the least. On the basis of presence of SSRs in the housekeeping genes, a phylogenetic relationship between these phytopathogenic prokaryotes was deduced and compared with the phylogeny developed based on 16S ribosomal RNA gene.

Compilación de oligonucleótidos para la detección y clasificación de fitoplasmas

Phytoplasmas are phytopathogenic prokaryotes of great importance because they have been linked to numerous diseases around the world. The aim of these research was to present the general characteristics, the size and composition of the genome and the genes and/or regions used as molecular markers for the identification and characterization of phytoplasmas. Among its main hosts are fruit and wood trees, vegetables, cut flowers and weeds, which generate alterations in the hormonal balance producing symptoms such as philodias and virescence. Because its isolation in vitro has not been possible, the detection and characterization has been carried out, mainly, with molecular techniques. In addition, the use of New Generation Sequencing (NGS) has allowed to know the complete genome of some phytoplasmas, as well as the regions and genes that constitute it. In the present bibliographic review, the information generated from the molecular techniques and NGS sequencing is compiled, as well as the primers reported to identify some groups of phytoplasmas.

Folate Biosynthesis Pseudogenes, ΨfolPand ΨfolK, and an O-Sialoglycoprotein Endopeptidase Gene Homolog in the Phytoplasma Genome

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.

Molecular biology in systematics and diagnosis of phytopathogenic prokaryotes

Molecular biology in systematics and diagnosis of phytopathogenic prokaryotes

Expression of the strA-strB streptomycin resistance genes in Pseudomonas syringae and Xanthomonas campestris and characterization of IS6100 in X. campestris

Expression of the strA-strB streptomycin resistance (SMr) genes was examined in Pseudomonas syringae pv. syringae and Xanthomonas campestris pv. vesicatoria. The strA-strB genes in P. syringae and X. campestris were encoded on elements closely related to Tn5393 from Erwinia amylovora and designated Tn5393a and Tn5393b, respectively. The putative recombination site (res) and resolvase-repressor (tnpR) genes of Tn5393 from E. amylovora, P syringae, and X. campestris were identical; however, IS6100 mapped within tnpR in X. campestris, and IS1133 was previously located downstream of tnpR in E. amylovora (C.-S Chiou and A. L. Jones, J. Bacteriol. 175:732-740, 1993). Transcriptional fusions (strA-strB::uidA) indicated that a strong promoter sequence was located within res in Tn5393a. Expression from this promoter sequence was reduced when the tnpR gene was present in cis position relative to the promoter. In X. campestris pv. vesicatoria, analysis of promoter activity with transcriptional fusions indicated that IS6100 increased the expression of strA-strB. Analysis of codon usage patterns and percent G+C in the third codon position indicated that IS6100 could have originated in a gram-negative bacterium. The data obtained in the present study help explain differences observed in the levels of SMr expressed by three genera which share common genes for resistance. Furthermore, the widespread dissemination of Tn5393 and derivatives in phytopathogenic prokaryotes confirms the importance of these bacteria as reservoirs of antibiotic resistance in the environment.