Multilocus sequence analysis of 'Candidatus Phytoplasma asteris' strain and the genome analysis of Turnip mosaic virus co-infecting oilseed rape

AIM

Molecular characterization of a pathogenic complex infecting winter oilseed rape (Brassica napus ssp. oleifera (DC.) Metzg.) plants showing typical rape phyllody symptoms along with some atypical changes.

METHODS AND RESULTS

Phytoplasma ('Candidatus Phytoplasma') presence was confirmed by PCR-RFLP and 16S rRNA gene sequencing. Phylogenetic analyses of phytoplasma amp, tufB, secY, groEL and ribosomal protein genes confirmed its affiliation to the 'Ca. P. asteris' species. However, in the amp gene encoding a specific protein crucial for insect transmission specificity, significant SNPs were found. Biological and serological tests revealed the co-infection with Turnip mosaic virus (TuMV). The phylogenetic analysis of full TuMV genome sequence, the first reported from the Balkans, classified it into the world-B phylogenetic lineage.

CONCLUSIONS

A pathogenic complex consisting of 'Ca. P. asteris' and TuMV found to co-infect oilseed rape plants for the first time was molecularly characterized.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rape phyllody is a serious problem in rapeseed production. The molecular information from this first multi-gene analysis of 'Ca. P. asteris' strain associated with rape phyllody as well as the first report of the complete sequence of TuMV isolate from the Balkans is a starting point for understanding the disease complexity and management.

Single-strand conformation polymorphism analysis for differentiating phytoplasma strains

Single-strand conformation polymorphism (SSCP) analysis is a sensitive and rapid technique for detecting DNA polymorphisms and mutations in PCR-amplified fragments. Due to its technical simplicity, it is widely used as a screening tool in various investigations, ranging from clinical diagnosis of human hereditary diseases to the characterization of microbial communities. This method can also be used successfully on phytoplasmas as a tool for the detection of molecular variability in conserved housekeeping genes such as 16S rRNA and tuf, as well as in more variable genes, revealing the presence of polymorphisms undetected by routine RFLP analyses. The reliability of SSCP has been confirmed by multiple alignments and phylogenetic analyses of representative sequences showing different SSCP profiles. However, it is not broadly applied in phytoplasma research yet. The technique provides an inexpensive, convenient, and sensitive method for determining sequence variation and to differentiate phytoplasma strains, and is particularly suitable for epidemiological studies or as a fast screening, typing tool when dealing with a large number of field samples.

Stem pitting and seedling yellows symptoms of Citrus tristeza virus infection may be determined by minor sequence variants

The isolates of Citrus tristeza virus (CTV), the most destructive viral pathogen of citrus, display a high level of variability. As a result of genetic bottleneck induced by the bud-inoculation of CTV-infected material, inoculated seedlings of Citrus wilsonii Tanaka displayed different symptoms. All successfully grafted plants showed severe symptoms of stem pitting and seedling yellows, while plants in which inoculated buds died displayed mild symptoms. Since complex CTV population structure was detected in the parental host, the aim of this work was to investigate how it changed after the virus transmission, and to correlate it with observed symptoms. The coat protein gene sequence of the predominant genotype was identical in parental and grafted plants and clustered to the phylogenetic group 5 encompassing severe reference isolates. In seedlings displaying severe symptoms, the low-frequency variants clustering to other phylogenetic groups were detected, as well. Indicator plants were inoculated with buds taken from unsuccessfully grafted C. wilsonii seedlings. Surprisingly, they displayed no severe symptoms despite the presence of phylogenetic group 5 genomic variants. The results suggest that the appearance of severe symptoms in this case is probably induced by a complex CTV population structure found in seedlings displaying severe symptoms, and not directly by the predominant genomic variant.

Purification of plant viral and satellite double-stranded RNAs on DEAE monoliths

Replicative double-stranded RNA (dsRNA) is useful in preliminary identification of Cucumber mosaic virus and its satellite RNA (satRNA). This plant pathogen complex yields sufficient quantity of the replicative RNA form that can be isolated by chromatography on chemically unmodified graded cellulose powder (CF-11). In this work, much faster and more efficient procedure using DEAE monoliths was developed in which dsRNA was separated from other species in total nucleic acids extract originating from the infected plant tissue. The developed chromatographic method revealed the pathogens' presence in only 15 min, avoiding nucleic acid precipitation and electrophoretic analysis.

[Congenital mesoblastic nephroma]

Four children with congenital mesoblastic nephroma were treated at the Children's University Hospital in Belgrade, between 1979 and 1990. In relation to the total number of children cured from renal tumours (44), diagnosis of congenital mesoblastic nephroma was confirmed in 9% of all cases with renal tumours. The age of all diagnosed patients was under one year. Three patients developed unilateral and one patient bilateral congenital mesoblastic nephroma. The authors also stress the importance of differential diagnosis between congenital mesoblastic nephroma and other renal tumours, since therapy and prognosis of these tumours are different. In a case of bilateral congenital mesoblastic nephroma that later relapsed with malignant alteration, it is questionable whether bilateral nephrectomy was the most appropriate treatment.

[Major and minor congenital anomalies in children with Wilms' tumor]

Wilms's tumour is a paediatric tumour of hereditary origin in 40% of cases. In children with Wilms's tumour associated congenital anomalies are frequent, particularly congenital anomalies of the kidney and urogenital tract. Over the period from 1972 to 1987 the authors carried out a prospective study and systematically investigated congenital major and minor anomalies in 24 children with Wilms's tumour. They revealed the presence of aniridia, bilateral cataract and cryptorchidism in 1/24 children, mental retardation, small stigated congenital major and minor anomalies in 40 chidism in 1/40 children, mental retardation, small stature and a cystic kidney in 1/40, mental retardation in 3/40. A detailed investigation of minor anomalies confirmed the presence of 2 to 3 anomalies in all observed children. Cytogenetic investigation was performed in all children. Only in a child with aniridia Wilms's tumour a cytogenetic anomaly, 11p deletion, was found.