'Candidatus Phytoplasma solani' interferes with the distribution and uptake of iron in tomato.

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.

Physicochemical and Sensory Properties of Cold Pressed Oils from Florida Hamlin and Valencia Oranges Affected by Huanglongbing.

Cold pressed oils from huanglongbing (HLB) symptomatic (SY) and asymptomatic (AS) Hamlin and Valencia oranges were assessed for 2 y (2014 to 2015 and 2015 to 2016 seasons) with 2 harvest dates for each orange variety per year. Physicochemical properties (optical rotation, aldehyde content, ultraviolet [UV] absorbance, refractive index, and specific gravity) mandated by the United States Pharmacopeia (USP) for orange oil quality were assessed. Hamlin and Valencia oils showed minor differences in physicochemical properties based upon disease stage. However, all Hamlin oils had aldehyde contents below the USP minimum and Valencia oil from late season SY oranges had specific gravities above the USP maximum. Significant differences based on harvest year were seen for aldehyde content, refractive index, optical rotation, and UV absorbance. While none of these changes led to an oil being out of USP specifications, they indicate a need to monitor the quality of oil every year to ensure a consistent product. Flavor taste panels were performed both years by adding 0.035% oil samples to a uniform orange juice base. Aroma panels were done by smelling pure oil. There were no significant differences between SY and AS oils for flavor, although panelist race was a significant factor in several of the panels. There were significant differences between the aroma of SY and AS oils for both 2015 to 2016 Hamlin Early and Valencia Late samples. Overall, these results show HLB can have an effect on the aroma and USP mandated physicochemical properties of Florida orange oils, although flavor may be unaffected by this plant disease.

Pathogen-induced release of plant allomone manipulates vector insect behavior.

Infochemicals mediate communication within and between different trophic levels. In this study, we identified a new type of plant allomone induced by a plant pathogen and perceived by its vector insect Cacopsylla picta. This phloem-feeding psyllid is the main vector of Candidatus Phytoplasma mali, a cell wall-lacking bacterium that causes the so-called apple proliferation disease. In a previous study, we showed that newly emerged females of C. picta were attracted by the odor of phytoplasma-infected apple plants (Malus domestica), which release ss-caryophyllene in contrast to uninfected plants. Here, the attractiveness of this sesquiterpene for C. picta was confirmed in both olfactometer bioassays and field studies. Synthetic ss-caryophyllene was highly attractive to newly emerged adults of C. picta both when offered simultaneously with healthy apple odor and without. The psyllid's response was independent of its odor experience and infection status. These results confirm our previously established hypothesis that this phytoplasma manipulates the behavior of its vector insect by changing the odor blend of its host plant. Deployed in apple orchards, sticky traps baited with ss-caryophyllene dispensers caught both males and females of C. picta. Consequently, this new type of infochemical, i.e., a phytopathogen-induced plant allomone, represents a promising compound to develop innovative techniques for monitoring or maybe even mass trapping of C. picta.