Alternative oxidase impacts the plant response to biotic stress by influencing the mitochondrial generation of reactive oxygen species

Previously, we showed that inoculation of tobacco with Pseudomonas syringae incompatible pv. maculicola results in a rapid and persistent burst of superoxide (O₂^‐) from mitochondria, no change in amount of mitochondrial alternative oxidase (AOX) and induction of the hypersensitive response (HR). However, inoculation with incompatible pv. phaseolicola resulted in increased AOX, no O₂^‐ burst and no HR. Here, we show that in transgenic plants unable to induce AOX in response to pv. phaseolicola, there is now a strong mitochondrial O₂^‐ burst, similar to that normally seen only with pv. maculicola. This interaction did not however result in a HR. This indicates that AOX amount is a key determinant of the mitochondrial O₂^‐ burst but also that the burst itself is not sufficient to induce the HR. Surprisingly, the O₂^‐ burst normally seen towards pv. maculicola is delayed in plants lacking AOX. This delay is associated with a delayed HR, suggesting that the burst does promote the HR. A O₂^‐ burst can also be induced by the complex III inhibitor antimycin A (AA), but is again delayed in plants lacking AOX. The similar mitochondrial response induced by pv. maculicola and AA suggests that electron transport is a target during HR‐inducing biotic interactions.     

A molecular phylogenetic appraisal of the systematics of the Aglaopheniidae (Cnidaria: Hydrozoa,Leptothecata) from the north‐east Atlantic and west Mediterranean

The hydrozoan family Aglaopheniidae (Cnidaria) is widespread worldwide and contains some of the most easily recognizable hydroids because of their large colony size and characteristic microscopic structure. The systematics of the group has, however, been controversial and dedicated molecular analyses are lacking. We therefore analysed existing and new 16S rRNA sequences of Aglaopheniidae, in a total of 98 16S sequences corresponding to 25 putative species (25 nominal and three undescribed) from seven genera. The monophyly of the subfamilies Gymnangiinae and Aglaopheniinae, and tribes Aglaopheniini and Cladocarpini were not verified with 16S sequence data. The genera Gymnangium and Aglaophenia can only be considered valid if both Gymnangium gracicaule and Aglaophenia latecarinata are removed from their respective genera. The phenotypically similar Cladocarpus and Streptocaulus are probably monophyletic and clearly distinct genetically. The genus Lytocarpia may be polyphyletic. The nominal species Aglaophenia pluma, Aglaophenia tubiformis, and Aglaophenia octodonta are probably conspecific, as are also the species Aglaophenia acacia and Aglaophenia elongata. The 16S data revealed the existence of two potentially unnamed species of Aglaophenia respectively from the Azores and Madeira. The phylogeographical structure of the taxa with the greatest representation of haplotypes from the north‐east Atlantic and Mediterranean, revealed the influence of Mediterranean waters in Madeira and the Azores, and gene flow between deep waters of the Mediterranean and Atlantic. The last glaciations in Europe may have caused genetic bottlenecks but also high intraspecific haplotype diversity. Finally, Macrorhynchia philippina was detected in samples from Madeira and possibly represents an invasive species. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 717–727.     

Consequences of grazing on the vertical transmission of a fungal Neotyphodium symbiont in an annual grass population

Symbiosis between cool‐season grasses and vertically transmitted fungal endophytes are common and significantly impact on ecosystem function. This makes the understanding of the underlying mechanisms to symbiotic individuals frequency in local populations much more interesting. Most studies have been focused on the differential fitness between symbiotic and non‐symbiotic counterparts (relative fitness), barely considering other mechanisms. We performed a microcosms experiment to evaluate whether grazing alters the dynamics of the endophyte Neotyphodium occultans in the annual grass Lolium multiflorum by simultaneously modifying the relative fitness and the endophyte efficiency to be transmitted from host plants to seeds. Grazing was simulated by means of clipping and trampling on symbiotic and non‐symbiotic plants growing separately, in soils obtained from paddocks, differing in their agronomic management history (natural grassland vs. ryegrass promotion). Seed production showed a complex pattern as it depended on the symbiotic status of the plants, the level of grazing and the agro‐ecological context. Grazed plants produced three times fewer seeds than ungrazed plants only in microcosms with endophyte‐symbiotic plants in soils from ryegrass promotion. Endophyte benefits on seed production were exclusively observed in ungrazed plants in the same soil. Symbiotic plants produced symbiotic and non‐symbiotic seeds in all the treatments. While the production of non‐symbiotic seeds by these plants was not affected by grazing and the soil, grazing reduced the production of symbiotic seeds in both contexts. Grazing negative effect on the density of fully infected spikes determined a significant increment in the transmission failures which were not modified by agro‐ecological contexts. Therefore, grazing can modulate symbiosis dynamics through reducing seed production and endophyte transmission efficiency. Transmission has been disregarded, but it is a context‐dependent process that could lead to a gradual reduction in the symbiotic plants frequency in a population if the mutualism effectiveness does not outweigh transmission failures.     

The Torradovirus‐specific RNA2‐ORF1 protein is necessary for plant systemic infection

Tomato apex necrosis virus (ToANV, species Tomato marchitez virus, genus Torradovirus, family Secoviridae) causes a severe tomato disease in Mexico. One distinctive feature of torradoviruses compared with other members of the family Secoviridae is the presence of an additional open reading frame (ORF) in genomic RNA2 (denominated RNA2‐ORF1), located upstream of ORF2. RNA2‐ORF2 encodes a polyprotein that is processed into a putative movement protein and three capsid proteins (CPs). The RNA2‐ORF1 protein has homologues only amongst other torradoviruses and, so far, no function has been associated with it. We used recombinant and mutant ToANV clones to investigate the role of the RNA2‐ORF1 protein in various aspects of the virus infection cycle. The lack of a functional RNA2‐ORF1 resulted in an inability to systemically infect Nicotiana benthamiana and tomato plants, but both positive‐ and negative‐strand RNA1 and RNA2 accumulated locally in agroinfiltrated areas in N. benthamiana plants, indicating that the RNA2‐ORF1 mutants were replication competent. Furthermore, a mutant with a deletion in RNA2‐ORF1 was competent for virion formation and cell‐to‐cell movement in the cells immediately surrounding the initial infection site. However, immunological detection of the ToANV CPs in the agroinfiltrated areas showed that this mutant was not detected in the sieve elements even if the surrounding parenchymatic cells were ToANV positive, suggesting a role for the RNA2‐ORF1 protein in processes occurring prior to phloem uploading, including efficient spread in inoculated leaves.     

The autophagy genes atg8 and atg1 affect morphogenesis and pathogenicity in Ustilago maydis

Autophagy is a complex degradative process in which cytosolic material, including organelles, is randomly sequestered within double‐membrane vesicles termed autophagosomes. In Saccharomyces cerevisiae, the autophagy genes ATG1 and ATG8 are crucial for autophagy induction and autophagosome assembly, respectively, and their deletion has an impact on the autophagic potential of the corresponding mutant strains. We were interested in the role of autophagy in the development and virulence of U. maydis. Using a reverse genetic approach, we showed that the U. maydis ATG8 orthologue, atg8, is associated with autophagy‐dependent processes. Deletion of atg8 abolished autophagosome accumulation in the vacuoles of carbon‐starved cells and drastically reduced the survival of U. maydisΔatg8 mutant strains during these conditions. In addition, atg8 deletion had an impact on the budding process during saprobic haploid growth. The infection of maize with compatible Δatg8 strains resulted in fewer galled plants, and fungal gall colonization was strongly reduced, as reflected by the very low hyphal density in these tissues. Δatg8 infections resulted in the formation of very few teliospores. To corroborate the role of autophagy in U. maydis development, we also deleted the ATG1 orthologue, atg1. Deletion of atg1 yielded phenotypes similar to the Δatg8 strains during saprobic growth, but of lower magnitude. The Δatg1 strains were only slightly less pathogenic than the wild‐type and teliospore production was not affected. Surprisingly, atg1 deletion in the Δatg8 background exacerbated those phenotypes already observed in the Δatg8 and Δatg1 single‐mutant strains, strongly suggesting an additive phenotype. In particular, the double mutant was completely suppressed for plant gall induction.     

Myrtlemiris,a new genus and new species of Australian plant bugs (Insecta: Heteroptera: Miridae): systematics,phylogeny and host associations

A new Australian genus of Orthotylinae, Myrtlemiris Cheng, Mututantri & Cassis gen.n. , is described, with nine included species described as new to science (M. agnew sp.n. , M. astartephila sp.n. , M. meanarra sp.n. , M. newmanensis sp.n. , M. rubrocuneatus sp.n. , M. russulatus sp.n. , M. silveirae sp.n. , M. tesselatus sp.n. , M. yalgoo sp.n. ). A phylogenetic analysis based on 39 morphological characters is presented for all Myrtlemiris species and 6 outgroup taxa. This analysis establishes Myrtlemiris as monophyletic, defined by a broad apophysis on the left paramere. A key to species is provided and diagnostic characters are illustrated. Myrtlemiris is endemic to southwest Western Australia. Host plants for Myrtlemiris species are near restricted to the myrtaceous tribe Chamelaucieae.     

Inhibition of fusicoccin-stimulated K+/H+ transport in root tips from maize seedlings pretreated with Chlorsulfuron

Abstract Fusicoccin (FC)-stimulated K⁺ (₈₆Rb) uptake and proton extrusion of maize (Zea mays) root apical segments were inhibited by pretreatment of 4-day-old seedlings with the herbicide Chlorsulfuron. In the range of Chlorsulfuron concentrations 0.01-10 mmol m^?3, the percentage of inhibition was 15% at 0.01 mmol m^?3 and progressively increased with Chlorsulfuron concentration up to 60% at 10 mmol m^?3. At the maximum concentration tested (10 mmol m^?3), the inhibition was evident after 1.5 h of pre-treatment. The binding of FC to microsomal fractions of root segments from Chlorsulfuron-pretreated seedlings was inhibited by 30%. It is suggested that Chlorsulfuron causes an alteration at the plasmalemma level involving the FC binding sites. The ineffectiveness of Chlorsulfuron in inhibiting FC-stimulaled K⁺ uptake when administered to excised segments, while inhibiting the enzyme acetolactate synthase, pointed out by Ray (1984) as the site of action of Chlorsulfuron in pea plants, suggests that the observed inhibition of K⁺ uptake and H⁺ extrusion is not induced by Chlorsulfuron inhibition of this enzyme. An alternative site of action of Chlorsulfuron is hypothesized in maize plants.     

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.