Cytoskeleton functions in plant–microbe interactions

The plant cytoskeleton consists of actin filaments and microtubules and plays a pivotal role as mediator of intracellular transport processes. In addition to this essential cellular housekeeping task it significantly contributes to the establishment of cell polarity during plant development and morphogenesis. Rapid changes in regular cytoskeleton architecture occur upon contact of individual plant cells with both pathogenic and symbiotic microbes. In the case of pathogens, polarized cytoskeletal rearrangements are thought to allow the localized delivery of cargo for defense execution, while in symbiotic interactions the reorganization may advance establishment of the symbiotic relationship. Although firm experimental evidence for these facts is lacking to date, it is believed that microbial metabolites and effector proteins are released into plant cells for manipulation of the host cytoskeleton, while some secreted plant defensive polypeptides may target the microbial cytoskeleton. This would be consistent with the recent finding that cytoskeletal functions are not only crucial for plant defense but likewise essential during various stages of microbial pathogenesis. The cytoskeleton thus emerges as a potential mutual target in plant–pathogen combats that appears to be under attack by effector molecules from both sides.     

Drought as a modulator of plant–virus–vector interactions: Effects on symptom expression,plant immunity and vector behaviour

Plant–virus interactions are affected by environmental conditions that determine plant vulnerability to pathogens and the population dynamics of insect vectors. We hypothesize that drought enhances horizontal transmission by dampening the basal immunity of plants, which triggers symptom expression and vector manipulation. The potato yellow vein virus (PYVV) causes potato yellow vein disease (PYVD), a re-emerging epidemic of potato crops in South America, and is transmitted horizontally by the greenhouse whitefly (GWF), Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), or vertically through infected seed tubers. We investigated the role of drought and temperature as modulators of PYVD symptom expression, plant immune response, and vector survival, development and host preference. We found that drought induced symptom expression, suppressed the salicylic acid pathway and increased PYVV replication. GWF survival was reduced on PYVV-infected hosts and development was slowest when they fed on plants with PYVD symptoms, which also triggered adults’ attraction to PYVV-infected plants. However, adults previously fed on infected plants showed the opposite effect, being more attracted to PYVV-free plants. We propose a theoretical model that explains the role of drought in modulating potato–PYVV–GWF interactions and provides new insights into plant–virus–vector coevolution.     

Temporal modulation of oxidant and antioxidative responses in Brassica carinata during β-aminobutyric acid-induced resistance against Alternaria brassicae

A preinoculative foliar application of 5 mM BABA significantly inhibited the colonization of Alternaria brassicae on leaves of Brassica carinata susceptible cultivar car6. BABA treatment led to transient but significant increase in H₂O₂ level during early stages of pathogen colonization. A significant increase in superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol dependent peroxidase (GDP) contributed to inhibition of the oxidative stress in BABA treated plants in response to pathogen infection. In conclusion BABA treatment led to proper balance of oxidant & antioxidants suitable for expression of resistance resulting in curtail of pathogen ingress during early stages of colonization.     

Post-translational modifications in effectors and plant proteins involved in host–pathogen conflicts

Molecular interplay between two species is largely driven by protein–protein interactions and protein modifications that set the pace of co-evolution in these species. During host–pathogen interactions, proteins involved in virulence and defence impart tempospatial dynamic post-translational modifications (PTMs) to gain advantage for the causative species. Pathogens mainly cause disease in plant hosts by secreting elicitors (peptides and small molecules) or proteins in the inter- and intracellular space of host cells. These pathogen proteins have evolved a wide array of sophisticated mechanisms to manipulate host responses, including resistance. Through a set of diverse events ranging from PTMs to post-translational oligomerization, these proteins are able to enhance virulence and suppress the otherwise elaborate plant immune system. Similarly, PTMs adapted by host proteins often lead to the activation of a robust defence response. Insights into the PTMs of pathogen and host proteins are therefore germane to the understanding of the co-evolutionary arms race. This review summarizes the characterization of PTMs in pathogen effectors and their target host proteins. Based on this, a metaphorical view of host–pathogen conflicts is proposed, where PTMs act as molecular pivots in a 3D combinatorial game model – a novel abstraction of the arms race, where these molecular pivots restore the balance of competition between the two organisms.     

Breakdown of plant virus resistance: can we predict and extend the durability of virus resistance?

Cultivars with introgressed natural resistance genes have been widely used for plant disease control, especially in the control of virus diseases, for which no effective chemical control agent is available. However, we often encounter virus mutants that break down or overcome the resistance. In this review, recent studies will be discussed with respect to breakdown of plant virus resistance.     

Powdery mildew of Arabidopsis thaliana: a pathosystem for exploring the role of silicon in plant–microbe interactions

Silicon (Si) has been used in agriculture to protect plants against disease for hundreds of years and its prophylactic effects in monocots and dicots are well documented. The mechanisms by which Si exerts its protective effects in planta, however, are uncertain and presently the subject of debate. In this study, we sought to determine if Arabidopsis thaliana could be used to clarify the role of Si in plant–pathogen interactions. Accordingly, X-ray microanalysis mapping, light microscopy, scanning and transmission electron microscope techniques were used to examine the leaves of Si− fed A. thaliana plants inoculated with the powdery mildew fungus, Erysiphe cichoracearum. The results of this study demonstrate for the first time, that A. thaliana is a species that absorbs Si and that the incidence of powdery mildew disease for Si− fed plants is significantly lower compared to control plants. In particular, treatment with Si appeared to induce the production of an electron-dense, fungitoxic substance that accumulated within and around the collapsed fungal haustoria of infected epidermal cells within the leaves of disease-resistant plants. These results with Arabidopsis corroborate recent observations in other non-related species and support the emerging theory that the mechanisms by which Si imparts resistance to plants are complex and are not entirely explained by the traditionally proposed role of Si as a reinforcer of mechanical resistance. Collectively, the findings of the present study have established the Arabidopsis thaliana-Erysiphe cichoracearum pathosystem as a valid model to investigate the role of Si in plant–microbe interactions.     

Mechanism of plant–microbe interaction and its utilization in disease-resistance breeding for modern agriculture

Plant diseases pose a major and constant threat to crop production and food security in modern agriculture. While application of pesticides can be a cost to the environment and human health, development and utilization of resistant cultivars is the most effective, economical, and eco-friendly approach to disease control. Using resistant cultivars is especially important for organic agriculture. Increasing breakthroughs have been made in understanding the mechanism of plant–microbe interaction. A current challenge now is how to apply the new knowledge to more effectively create disease-resistant crop cultivars. Integration of plant breeding and plant pathology is necessary to underpin crop improvement for food and other plant-based production. In this review, we summarize our current understanding on the mechanism of plant–microbe interaction and discuss the strategies for disease-resistance breeding of crop cultivars.     

Historical virus isolate collections: An invaluable resource connecting plant virology’s pre-sequencing and post-sequencing eras

Many laboratories maintain historical collections of preserved plant virus isolates that store a wealth of untapped data, including original type isolates, studied in the pre-sequencing era. Currently, many recently recognized virus species exist with no supporting reference sequences. Also, many virus sequences appear new when compared to available sequences, but, on sequencing pre-sequencing era isolates, they may coincide. Such linkages allow access to data from previously determined biological and other parameters from pre-sequencing era studies. These linkages are increasingly being found using high-throughput sequencing, helping clarify virus taxonomy and improving understanding of virus ecology and evolution. Thus, mistakes can be avoided in naming viruses and in combining or separating them, as well as enabling identification of unknown viruses preserved long ago. With well-established viruses, success in dating and other evolutionary studies, and discovery of changes in regional virus populations, both depend upon comparisons between recent and old isolate sequences covering the greatest possible time periods. Such studies help reveal the extent that human activities have influenced virus evolution and changed virus populations on a global scale. Sequencing virus genomes from herbarium specimens, archaeological specimens, or living plant collections can provide complementary data. By bringing context to newly detected viruses and supporting plant pest risk analyses, linking new virus discoveries to previously generated disease symptom, host range, virus transmission, and geographical distribution data has important implications for plant health regulation. Also, historical isolates can provide an invaluable resource facilitating biosecurity investigations involving virus introductions, entry pathways, and baseline surveillance.     

Potential plant–aphid–fungal associations aiding conservation biological control of cereal aphids in Argentina

The overall aim of this study was to identify potential associations between aphids and plants as reservoirs of entomophthoralean fungi. A survey of weeds associated with wheat field borders in two different localities was performed over two years, from April 2010 to April 2012 in the Pampeana central region, Argentina. On each sampling date, five individuals of each plant species were randomly selected, and healthy and infected aphids were collected and quantified once a month. The taxonomic identities of both aphid hosts and entomophthoralean fungi were established. Aphid–fungus associations identified as favorable for inclusion in conservation biological control strategies in borders of wheat crops are the following: Sonchus oleraceus (L.)/Hyperomyzus carduellinus (Theobald), Uroleucon sonchi (L.)/Pandora neoaphidis (Remaudière & Hennebert) Humber; S. oleraceus (L.)/H. carduellinus (Theobald)/Zoophthora radicans (Brefeld) Batko; Lamium amplexicaule (L.)/Cryptomyzus korschelti Bôrner/P. neoaphidis, Z. radicans, Entomophthora planchoniana Cornu; Foeniculum vulgare (Miller)/Dysaphis apiifolia (Theobald)/Z. radicans; Morrenia brachystephana Griseb/Aphis nerii Boyer de Fonscolombe/P. neoaphidis and Brassica rapa L./Brevicoryne brassicae (L.)/P. neoaphidis.     

Beet necrotic yellow vein virus genome reassortments in a resistant sugar beet variety showing–in a small area in France–strong rhizomania symptoms

Journal of Plant Diseases and Protection - The genome composition of Beet necrotic yellow vein virus (BNYVV) was analysed in rootlets of field-grown sugar beets belonging to a variety which in...     

Improved method for in situ biolistic transformation to analyze barley–powdery mildew interactions

Although the use of stable transformants is indispensable to elucidate mechanisms underlying molecular plant–pathogen interactions, this approach remains difficult to apply to crops. Alternatively, biolistic transformation has often been used as a transient expression method in various plants. In this study, we developed a method for in situ biolistic transformation without separating leaves from barley seedlings by using a hand-held particle bombardment system because unwounded leaves are preferable for analyzing interactions between barley and Blumeria graminis f. sp. hordei which requires healthy living cells. As a result, we found that the infection rate in intact leaves was higher than in separated leaves and that the transformation efficiencies in leaves were higher when plants were grown in vermiculite rather than in culture soil. Furthermore, we determined the appropriate inoculation time after bombardment to analyze the incompatible interaction and successfully monitored the gradual occurrence of cell death over time. Our system was suitable for relatively long-term follow-up analysis of the fate of each single cell during plant–pathogen interactions.     

Pheromone Research and Development in Israel 1975–2015

The review describes the history of pheromone research in Israel in 1975–2015. The research focused on sex pheromones of moths that were important agricultural pests. Identification, synthesis and field application of sex pheromones was performed. Synthetic procedures of several known sex pheromones were developed. Monitoring and control of key pest moths was evaluated. The interactions of pheromone components of closely related species were studied in field and laboratory experiments. The sex pheromones of three scale insects, two mealybug species and Matsucoccus josephi were studied. New syntheses were developed and the pheromones were implemented in pest management. Structure activity relationship of the pheromonal and kairomonal of the M. josephi pheromone was investigated. Different pherotypes of P. ficus were identified and evaluated. The aggregation pheromone of sap beetles in combination with food baits was evaluated. The aggregation pheromone of the almond bark beetle was identified and a stereospecific synthesis of its enantiomers was developed. Monitoring the pest in stone fruit orchards was implemented. The activity of the pheromone biosynthesis activating neuropeptide (PBAN) was studied in Helicoverpa armigera and Heliothis peltigera. The ligation technique was used to assess the effect of PBAN on the production of female and male pheromones. A structure-activity relationship study of PBAN indicated that shorter peptides display activity as the full length PBAN. A series of linear and cyclic peptide analogs was prepared, resulting in the discovery of a lead antagonist. The research and development activity facilitated the intensive integration of pheromones in the pest management regimes in Israeli agriculture.     

Do aeolian deposits and sand encroachment intensity shape patterns of vegetation diversity and plant functional traits in desert pavements?

The effects of sand encroachment on composition, diversity, and functional patterns of vegetation in drylands are rarely studied, and yet addressing these aspects is important to deepen our understanding of the biodiversity conservation. This study aimed to investigate the effect of sand encroachment on plant functional biodiversity of desert pavements(gravel deserts) in the Sahara Desert of Algeria. Plants were sampled and analyzed in three desert pavements with different levels of sand encroac...