Virus effects on plant quality and vector behavior are species specific and do not depend on host physiological phenotype

There is growing evidence that plant viruses manipulate host plants to increase transmission-conducive behaviors by vectors. Reports of this phenomenon frequently include only highly susceptible, domesticated annual plants as hosts, which constrains our ability to determine whether virus effects are a component of an adaptive strategy on the part of the pathogen or simply by-products of pathology. Here, we tested the hypothesis that transmission-conducive effects of a virus (Turnip yellows virus [TuYV]) on host palatability and vector behavior (Myzus persicae) are linked with host plant tolerance and physiological phenotype. Our study system consisted of a cultivated crop, false flax (Camelina sativa) (Brassicales: Brassicaceae), a wild congener (C. microcarpa), and a viable F1 hybrid of these two species. We found that the most tolerant host (C. microcarpa) exhibited the most transmission-conducive changes in phenotype relative to mock-inoculated healthy plants: Aphids preferred to settle and feed on TuYV-infected C. microcarpa and did not experience fitness changes due to infection—both of which will increase viruliferous aphid numbers. In contrast, TuYV induced transmission-limiting phenotypes in the least tolerant host (C. sativa) and to a greater degree in the F1 hybrid, which exhibited intermediate tolerance to infection. Our results provide no evidence that virus effects track with infection tolerance or physiological phenotype. Instead, vector preferences and performance are driven by host-specific changes in carbohydrates under TuYV infection. These results provide evidence that induction of transmission-enhancing phenotypes by plant viruses is not simply a by-product of general pathology, as has been proposed as an explanation for putative instances of parasite manipulation by viruses and many other taxa

Cascading effects of N input on tritrophic (plant-aphid-parasitoid) interactions

International audienceBecause N is frequently the most limiting mineral macronutrient for plants in terrestrial ecosystems, modulating N input may have ecological consequences through trophic levels. Thus, in agro-ecosystems, the success of natural enemies may depend not only from their herbivorous hosts but also from the host plant whose qualities may be modulated by N input. We manipulated foliar N concentrations by providing to Camelina sativa plants three different nitrogen rates (control, optimal, and excessive). We examined how the altered host-plant nutritional quality influenced the performances of two aphid species, the generalist green peach aphid, Myzus persicae, and the specialist cabbage aphid, Brevicoryne brassicae, and their common parasitoid Diaeretiella rapae. Both N inputs led to increased N concentrations in the plants but induced contrasted concentrations within aphid bodies depending on the species. Compared to the control, plant biomass increased when receiving the optimal N treatment but decreased under the excessive treatment. Performances of M.persicae improved under the optimal treatment compared to the control and excessive treatments whereas B.brassicae parameters declined following the excessive N treatment. In no-choice trials, emergence rates of D.rapae developing in M.persicae were higher on both optimum and excessive N treatments, whereas they remained stable whatever the treatment when developing in B.brassicae. Size of emerging D.rapae females was positively affected by the treatment only when it developed in M.persicae on the excessive N treatment. This work showed that contrary to an optimal N treatment, when N was delivered in excess, plant suitability was reduced and consequently affected negatively aphid parameters. Surprisingly, these negative effects resulted in no or positive consequences on parasitoid parameters, suggesting a buffered effect at the third trophic level. Host N content, host suitability, and dietary specialization appear to be major factors explaining the functioning of our studied system

De novo shoot organogenesis: from art to science

In vitro shoot organogenesis and plant regeneration are crucial for both plant biotechnology and the fundamental study of plant biology. Although the importance of auxin and cytokinin has been known for more than six decades, the underlying molecular mechanisms of their function have only been revealed recently. Advances in identifying new Arabidopsis genes, implementing live-imaging tools and understanding cellular and molecular networks regulating de novo shoot organogenesis have helped to redefine the empirical models of shoot organogenesis and plant regeneration. Here, we review the functions and interactions of genes that control key steps in two distinct developmental processes: de novo shoot organogenesis and lateral root formation

Arabidopsis shoot organogenesis is enhanced by an amino acid change in the ATHB15 transcription factor

International audienceThe hoc mutant displays high organogenic competence for in vitro shoot regeneration without addition of exogenous phytohormones. The genetic basis of this phenotype is investigated here. Using genetic mapping, the HOC locus was identified on chromosome 1. A point mutation was found in the At1g52150 gene, which encodes ATHB15/CORONA/INCURVATA4, a class III HD-ZIP transcription factor. The mutation replaced a serine with a cysteine in the MEKHLA domain of the protein. The wild-type ATHB15 gene was able to complement the hoc phenotype. Organogenesis response experiments revealed that hoc organogenic capacity was affected by the genetic background, and that it was not caused by a loss of ATHB15 function but by an effect of the mutation on protein function

A seasonal study of nitrogen status in Miscanthus giganteus highlights a central role for asparagine and arginine

CT 2 ; Département BAPA seasonal study of nitrogen status in Miscanthus giganteus highlights a central role for asparagine and arginine. EMBO conference : the nitrogen nutrition of plants – Nitrogen 201

The fate of cumulative applications of N-15-labelled fertiliser in perennial and annual bioenergy crops

International audienceThe fate of nitrogen (N) fertiliser applied to bioenergy crops is a key issue to allow high biomass production while minimising environmental impacts due to N losses. The aim of this study was to follow the fate in the soil-plant system of N fertiliser applied to perennial (Miscanthus x giganteus and switchgrass), "semi-perennial" (fescue and alfalfa) and annual (sorghum and triticale) bioenergy crops. Crops received N-15-labelled fertiliser (urea ammonium nitrate solution) during 4 or 5 successive years on the same subplots, at a rate varying from 24 to 120 kg N ha(-1) yr(-1). Biomass production, N and N-15 removal at harvest were measured each year. The N-15 recovery in crop residues, non-harvested crop parts and soil was measured at the end of the N-15-labelling period. Perennial crops had higher biomass production but generally lower N-15 recovery in harvested biomass than other crops, particularly when harvested late (end of winter). At the end of the 4 or 5-year period, the proportion of N-15 recovered in harvested biomass was 13-34% for perennials, 23-38% for semi-perennials and 34-39% for annual crops. Perennial crops stored large amounts of N in their belowground organs; the mean N-15 recovery in these organs was 12%, corresponding to a N storage flux of 14 kg N ha(-1) yr(-1). The N-15 recovery in soil (including crop residues) was higher for perennials (average 36%) than semi-perennials (28%) and annual crops (19%), corresponding to a N immobilisation rate of 43,15 and 12 kg N ha(-1) yr(-1) respectively. The mean overall N-15 recovery in the soil-plant system was 69% in perennials, 61% in semi-perennials to 56% in annual crops, suggesting that important fertiliser losses occurred through volatilisation and denitrification. Perennial bioenergy crops had the better efficiency by storing fertiliser-N in soil organic matter and living belowground biomass used as N reserves for succeeding years. (C) 2016 Elsevier B.V. All rights reserved

Identification of Phenotypic and Physiological Markers of Salt Stress Tolerance in Durum Wheat (Triticum Durum Desf.) through Integrated Analyses

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Sphingomonas sediminicola Dae20 Is a Highly Promising Beneficial Bacteria for Crop Biostimulation Due to Its Positive Effects on Plant Growth and Development

International audienceCurrent agricultural practices rely heavily on synthetic fertilizers, which not only consume a lot of energy but also disrupt the ecological balance. The overuse of synthetic fertilizers has led to soil degradation. In a more sustainable approach, alternative methods based on biological interactions, such as plant growth-promoting bacteria (PGPRs), are being explored. PGPRs, which include both symbiotic and free-living bacteria, form mutualistic relationships with plants by enhancing nutrient availability, producing growth regulators, and regulating stress responses. This study investigated the potential of Sphingomonas sediminicola Dae20, an α-Proteobacteria species commonly found in the rhizosphere, as a beneficial PGPR. We observed that S. sediminicola Dae20 stimulated the root system and growth of three different plant species in the Brassicaceae family, including Arabidopsis thaliana, mustard, and rapeseed. The bacterium produced auxin, nitric oxide, siderophores and showed ACC deaminase activity. In addition to activating an auxin response in the plant, S. sediminicola Dae20 exhibited the ability to modulate other plant hormones, such as abscisic acid, jasmonic acid and salicylic acid, which are critical for plant development and defense responses. This study highlights the multifunctional properties of S. sediminicola Dae20 as a promising PGPR and underscores the importance of identifying effective and versatile beneficial bacteria to improve plant nutrition and promote sustainable agricultural practices.</jats:p

<i>Sphingomonas sediminicola</i> Is an Endosymbiotic Bacterium Able to Induce the Formation of Root Nodules in Pea (<i>Pisum sativum</i> L.) and to Enhance Plant Biomass Production

The application of bacterial bio-inputs is a very attractive alternative to the use of mineral fertilisers. In ploughed soils including a crop rotation pea, we observed an enrichment of bacterial communities with Sphingomonas (S.) sediminicola. Inoculation experiments, cytological studies, and de novo sequencing were used to investigate the beneficial role of S. sediminicola in pea. S. sediminicola is able to colonise pea plants and establish a symbiotic association that promotes plant biomass production. Sequencing of the S. sediminicola genome revealed the existence of genes involved in secretion systems, Nod factor synthesis, and nitrogenase activity. Light and electron microscopic observations allowed us to refine the different steps involved in the establishment of the symbiotic association, including the formation of infection threads, the entry of the bacteria into the root cells, and the development of differentiated bacteroids in root nodules. These results, together with phylogenetic analysis, demonstrated that S. sediminicola is a non-rhizobia that has the potential to develop a beneficial symbiotic association with a legume. Such a symbiotic association could be a promising alternative for the development of more sustainable agricultural practices, especially under reduced N fertilisation conditions