Publications

4366

Abstract Background ‘Candidatus Phytoplasma solani’ is endemic in Europe and infects a wide range of weeds and cultivated plants. Phytoplasmas are prokaryotic plant pathogens that colonize the sieve elements of their host plant, causing severe alterations in phloem function and impairment of assimilate translocation. Typical symptoms of infected plants include yellowing of leaves or shoots, leaf curling, and general stunting, but the molecular mechanisms underlying most of the reported changes remain largely enigmatic. To infer a possible involvement of Fe in the host-phytoplasma interaction, we investigated the effects of ‘Candidatus Phytoplasma solani’ infection on tomato plants (Solanum lycopersicum cv. Micro-Tom) grown under different Fe regimes. Results Both phytoplasma infection and Fe starvation led to the development of chlorotic leaves and altered thylakoid organization. In infected plants, Fe accumulated in phloem tissue, altering the local distribution of Fe. In infected plants, Fe starvation had additive effects on chlorophyll content and leaf chlorosis, suggesting that the two conditions affected the phenotypic readout via separate routes. To gain insights into the transcriptional response to phytoplasma infection, or Fe deficiency, transcriptome profiling was performed on midrib-enriched leaves. RNA-seq analysis revealed that both stress conditions altered the expression of a large (> 800) subset of common genes involved in photosynthetic light reactions, porphyrin / chlorophyll metabolism, and in flowering control. In Fe-deficient plants, phytoplasma infection perturbed the Fe deficiency response in roots, possibly by interference with the synthesis or transport of a promotive signal transmitted from the leaves to the roots. Conclusions ‘Candidatus Phytoplasma solani’ infection changes the Fe distribution in tomato leaves, affects the photosynthetic machinery and perturbs the orchestration of root-mediated transport processes by compromising shoot-to-root communication.

AbstractIn order to devise a method for rapid detection of ‘Candidatus (Ca.) Phytoplasma pini’ and for distinguishing it rapidly from other phytoplasmas, we carried out preliminary sequencing of Lithuanian ‘Ca. Phytoplasma pini’ strain PineBL2 using Illumina (NGS) technology and targeted sequencing employing universal phytoplasma primers. We focused on two resulting chromosomal segments that contained a 16S rRNA gene and a translation elongation factor EF‐TU gene (tuf), respectively. Based on alignments of the ‘Ca. Phytoplasma pini’ gene sequences with the corresponding sequences of other phytoplasmas, we designed new primer pairs for PCR‐based detection of ‘Ca. Phytoplasma pini’. Because ‘Ca. Phytoplasma pini’ strains are expected to reside in the pine phloem in a very low titre, one might expect that they could be detected only by nested PCR. By contrast, the primers and PCR protocols designed in the current work enabled rapid direct PCR detection and identification of ‘Ca. Phytoplasma pini’ by amplifying a 484 bp 16S rDNA segment and a 513 bp tuf gene fragment that contain regions unique to this phytoplasma.

AbstractIn Argentina, amaranth is a promising crop due to high nutritional quality and ability to grow in a diversity of environments. In areas cultivated with amaranth, were observed plants exhibiting slow growth, deformed leaves, proliferation of shoots and malformed lateral panicles. Field survey revealed up to 96% disease incidence and 92% of the seeds collected from mother plants produced diseased seedlings. A phytoplasma was detected in association with seedlings and adult plants using nested PCR assays. Molecular identification by computer‐simulated RFLP and phylogenetic analysis evidenced the occurrence of a ‘Candidatus Phytoplasma hispanicum’‐related strain, affiliated with 16SrXIII‐A subgroup. The findings implicate amaranth as a new host for this subgroup and as a potential reservoir of the pathogen for other cultivated species. In addition, to the best of our knowledge, this study reports for the first time the presence of 16SrXIII‐A phytoplasma in Argentina and in South America. Furthermore, transmission assays pointed that naturally infected seed is an important vehicle of dissemination of the pathogen, threatening the expansion of the crop for new geographical areas.

AbstractBackgroundThe symbiosis between the olive fruit fly,Bactrocera oleae, andCandidatusErwinia dacicola has been demonstrated as essential for the fly’s larval development and adult physiology. The mass rearing of the olive fruit fly has been hindered by several issues, including problems which could be related to the lack of the symbiont, presumably due to preservatives and antibiotics currently used during rearing under laboratory conditions. To better understand the mechanisms underlying symbiont removal or loss during the rearing of lab colonies of the olive fruit fly, we performed experiments that focused on bacterial transfer from wild female flies to their eggs. In this research, eggs laid by wild females were treated with propionic acid solution, which is often used as an antifungal agent, a mixture of sodium hypochlorite and Triton X, or water (as a control). The presence of the bacterial symbiont on eggs was evaluated by real-time PCR and scanning electron microscopy.ResultsDGGE analysis showed a clear band with the same migration behavior present in all DGGE profiles but with a decreasing intensity. Molecular analyses performed by real-time PCR showed a significant reduction inCa. E. dacicola abundance in eggs treated with propionic acid solution or a mixture of sodium hypochlorite and Triton X compared to those treated with water. In addition, the removal of bacteria from the surfaces of treated eggs was highlighted by scanning electron microscopy.ConclusionsThe results clearly indicate how the first phases of the colony-establishment process are important in maintaining the symbiont load in laboratory populations and suggest that the use of products with antimicrobial activity should be avoided. The results also suggest that alternative rearing procedures for the olive fruit fly should be investigated.