Naslov
Phytoplasmas-progress in research of unique phytopathogenic bacteria

Autori
Šeruga, Martina ; Krajačić, Mladen ; Škorić, Dijana

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Zbornik = Proceedings / Treći hrvatski mikrobiološki kongres s međunarodnim sudjelovanjem, Poreč, 4.-7. listopada 2004. / Balenović, Mirta ; Wittner, Velimir - Zagreb : Hrvatsko mikrobiološko društvo, 2004, 83-84

Skup
Treći hrvatski mikrobiološki kongres s međunarodnim sudjelovanjem = Third Croatian Congress of Microbiology with International Participation

Mjesto i datum
Poreč, Hrvatska, 04.10.2004. - 07.10.2004

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
plant pathogens; 16S rRNA; PCR; RFLP; SSCP; grapevines; Lombardy poplar; phytoplasma genome

Sažetak
Phytoplasmas are prokaryotic plant pathogens belonging to the class Mollicutes. The lack of cell wall was one of the main reasons they had been named mycoplasma-like organisms (MLOs). Their genetic, functional and evolutionary distinctness was not recognized until 1993, when they were renamed phytoplasmas. These unique endocellular bacteria have the smallest known self-replicating genomes consisting of only 580-1350 kbp organized mainly in one circular chromosome. In some phytoplasmas, the existence of extrachromosomal elements has been confirmed. Aside from residing in plant phloem, phytoplasmas can live in sap-sucking insects primarily belonging to the families Cicadelloidae (leafhoppers) and Fulgoroidae (planthoppers), which are their main vectors in nature. Phytoplasmas can infect hundreds of plant species causing economically important diseases. Initial research on this group of plant disease agents primarily dealt with the biological aspects such as: host range of a phytoplasma, the type of symptoms induced in a plant host and the type of vector that can transmit the agent. Unlike other members of the class Mollicutes, phytoplasmas cannot be cultivated in vitro. Our inability to obtain axenic phytoplasma pure cultures still makes them difficult to investigate. Nevertheless, the developments in the field of molecular biology enabled new lines of research. Amplification of evolutionary conserved gene for 16S rRNA by direct and nested PCR as well as subsequent analyses of obtained amplicons by RFLP became the basis for sensitive phytoplasma detection and classification. The provisional taxonomic system encompasses more than 15 phytoplasma ribosomal groups and 40 subgroups. Other ribosomal genes, as well as elongation factor-Tu (tuf) and ribosomal protein genes, are also being used alternatively or in combination with 16S rDNA for finer phytoplasma distinction. In spite of the hindrances in phytoplasma research, the first complete genome sequence of a phytoplasma was published in January 2004. It has already shed new light on the minimal gene set essential for life and it is expected that, together with the other ongoing phytoplasma genome projects, it will move this type of research to the next level. A fresh view on the phytoplasma evolution and classification, the determination of factors involved in phytoplasma pathogenicity and the discovery of effective ways to control phytoplasma diseases are only some of the expected consequences. So far, we have reported the presence of phytoplasmas belonging to the ribosomal (sub)groups 16SrXII-A (stolbur or bois noir) and 16SrI-P (aster yellows). The latter is a member of newly discovered subgroup within the aster yellows group being detected, so far, only in the Lombardy poplar (Populus nigra L. 'Italica') trees from Zagreb area. RFLP analyses of other conserved genes such as tuf, BB88 and ribosomal protein rpL22 clearly confirmed that this is a molecularly distinguishable phytoplasma belonging also to a new ribosomal protein subgroup designated rp-O. It is possible that this phytoplasma could be specific for poplars and/or restricted only to the area of continental Croatia but further work on the epidemiology of this phytopathogen is needed to confirm these hypotheses. Phytoplasmas from the 16SrXII-A subgroup seem to be widespread throughout the country especially in the grapevines. We have been monitoring their geographical distribution and seasonal variations in the grapevines through PCR-RFLP 16SrRNA gene analyses. This approach, if not complemented by sequencing, does not allow the finer distinction of phytoplasmas belonging to the same subgroup having different epidemiology in the same plant host. To achieve this goal, still avoiding sequencing a large number of samples being screened, we have been trying to develop specific SSCP (single-strand conformation polymorphism analysis) protocols for screening various phytoplasma gene regions. If the relationships of SSCP profiles of a given gene region prove to be consistent with the sequence differences, the SSCP screenings could be applied in studying host-pathogen and pathogen-vector interactions at the molecular level.

Izvorni jezik
Engleski

Znanstvena područja
Biologija

POVEZANOST RADA