Roles of small RNAs in plant disease resistance

The interaction between plants and pathogens represents a dynamic competition between a robust immune system and efficient infectious strategies. Plant innate immunity is composed of complex and highly regulated molecular networks, which can be triggered by the perception of either conserved or race‐specific pathogenic molecular signatures. Small RNAs are emerging as versatile regulators of plant development, growth and response to biotic and abiotic stresses. They act in different tiers of plant immunity, including the pathogen‐associated molecular pattern‐triggered and the effector‐triggered immunity. On the other hand, pathogens have evolved effector molecules to suppress or hijack the host small RNA pathways. This leads to an arms race between plants and pathogens at the level of small RNA‐mediated defense.Here, we review recent advances in small RNA‐mediated defense responses and discuss the challenging questions in this area.     

Nitric oxide function in plant abiotic stress

Abiotic stress is one of the main threats affecting crop growth and production. An understanding of the molecular mechanisms that underpin plant responses against environmental insults will be crucial to help guide the rational design of crop plants to counter these challenges. A key feature during abiotic stress is the production of nitric oxide (NO), an important concentration dependent, redox‐related signalling molecule. NO can directly or indirectly interact with a wide range of targets leading to the modulation of protein function and the reprogramming of gene expression. The transfer of NO bioactivity can occur through a variety of potential mechanisms but chief among these is S‐nitrosylation, a prototypic, redox‐based, post‐translational modification. However, little is known about this pivotal molecular amendment in the regulation of abiotic stress signalling. Here, we describe the emerging knowledge concerning the function of NO and S‐nitrosylation during plant responses to abiotic stress.     

The in vivo synthesis of plant sesquiterpenes by Escherichia coli.

Three plant genes encoding (+)-delta-cadinene, 5-epi-aristolochene, and vetispiradiene cyclases were expressed in Escherichia coli to evaluate the potential of this bacterium to synthesize sesquiterpenes in vivo. Various growth temperatures, carbon sources, and host strains were examined to optimize terpene production. The highest levels of sesquiterpene production occurred when the enzymes were expressed in strain DH5alpha from the trc promoter (Ptrc) of the high-copy plasmidpTrc99A in M9 medium supplemented with 0.2% (v/v) glycerol at 30 degrees C for 5-epi-aristolochene and vetispiradiene and 37 degrees C for (+)-delta-cadinene. The highest concentrations of sesquiterpenes observed were 10.3 microg of (+)-delta-cadinene, 0.24 microg of 5-epi-aristolochene (measured as (+)-delta-cadinene equivalents), and 6.4 microg of vetispiradiene (measured as (+)-delta-cadinene equivalents) per liter of culture. These sesquiterpene production levels are >500-fold lower than carotenoid production, both of which are synthesized from endogenous trans-farnesyl diphosphate (FDP) in E. coli. Based on these results, we conclude that the limiting factor for sesquiterpene synthesis in E. coli is the poor expression of the cyclase enzyme and not supply of the FDP precursor.     

Emerging role of roots in plant responses to aboveground insect herbivory

Plants have evolved complex biochemical mechanisms to counter threats from insect herbivory. Recent research has revealed an important role of roots in plant responses to above ground herbivory (AGH). The involvement of roots is integral to plant resistance and tolerance mechanisms. Roots not only play an active role in plant defenses by acting as sites for biosynthesis of various toxins and but also contribute to tolerance by storing photoassimilates to enable future regrowth. The interaction of roots with beneficial soil‐borne microorganisms also influences the outcome of the interaction between plant and insect herbivores. Shoot‐to‐root communication signals are critical for plant response to AGH. A better understanding of the role of roots in plant response to AGH is essential in order to develop a comprehensive picture of plant‐insect interactions. Here, we summarize the current status of research on the role of roots in plant response to AGH and also discuss possible signals involved in shoot‐to‐root communication.     

Conventional and unconventional ubiquitination in plant immunity

Ubiquitination is one of the most abundant types of protein post‐translational modification (PTM) in plant cells. The importance of ubiquitination in the regulation of many aspects of plant immunity has been increasingly appreciated in recent years. Most of the studies linking ubiquitination to the plant immune system, however, have been focused on the E3 ubiquitin ligases and the conventional ubiquitination that leads to the degradation of the substrate proteins by the 26S proteasome. By contrast, our knowledge about the role of unconventional ubiquitination that often serves as non‐degradative, regulatory signal remains a significant gap. We discuss, in this review, the recent advances in our understanding of ubiquitination in the modulation of plant immunity, with a particular focus on the E3 ubiquitin ligases. We approach the topic from a perspective of two broadly defined types of ubiquitination in an attempt to highlight the importance, yet current scarcity, in our knowledge about the regulation of plant immunity by unconventional ubiquitination.     

The plant homeodomain finger protein MESR4 is essential for embryonic development in Drosophila

Misexpression Suppressor of Ras 4 (MESR4), a plant homeodomain (PHD) finger protein with nine zinc‐finger motifs has been implicated in various biological processes including the regulation of fat storage and innate immunity in Drosophila. However, the role of MESR4 in the context of development remains unclear. Here it is shown that MESR4 is a nuclear protein essential for embryonic development. Immunostaining of polytene chromosomes using anti‐MESR4 antibody revealed that MESR4 binds to numerous bands along the chromosome arms. The most intense signal was detected at the 39E‐F region, which is known to contain the histone gene cluster. P‐element insertions in the MESR4 locus, which were homozygous lethal during embryogenesis with defects in ventral ectoderm formation and head encapsulation was identified. In the mutant embryos, expression of Fasciclin 3 (Fas3), an EGFR signal target gene was greatly reduced, and the level of EGFR signal‐dependent double phosphorylated ERK (dp‐ERK) remained low. However, in the context of wing vein formation, genetic interaction experiments suggested that MESR4 is involved in the EGFR signaling as a negative regulator. These results suggested that MESR4 is a novel chromatin‐binding protein required for proper expression of genes including those regulated by the EGFR signaling pathway during development. genesis 53:701–708, 2015. © 2015 Wiley Periodicals, Inc.     

Glutathione S-transferases in the adaptation to plant secondary metabolites in the Myzus persicae aphid

Glutathione S-transferases (GST) in insects play an important role in the detoxification of many substances including allelochemicals from plants. Induction of GST activity in Myzus persicae in response to secondary metabolites from Brassica plants was determined using different host plant species and confirmed using artificial diet with pure allelochemicals added. The 2,4-dinitro-1-iodobenzene (DNIB) was found to be a useful substrate for identifying particular GSTs in insects. GSTs from M. persicae were purified using different affinity chromatography columns and related kinetic parameters were calculated. GST isoenzymes were characterised using electrophoretic methods. Although SDS-PAGE results indicated similarity among the purified enzymes from each affinity column, biochemical studies indicated significant differences in kinetic parameters. Finally, the GST pattern of M. persicae was discussed in terms of insect adaptation to the presence of plant secondary substances such as the glucosinolates and the isothiocyanates, from Brassicaceae host plants.     

Sex pheromone of the alfalfa plant bug,Adelphocoris lineolatus

In northern China, due to the large‐scale adoption of transgenic Bacillus thuringiensis Berliner (Bt) cotton, the number of Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae) has increased quickly, causing significant loss in cotton and alfalfa production. One of the environmentally safe strategies without use of pesticides is the application of insect pheromone for mating disruption. In our study, we aim to identify the active components in sexually mature virgin female A. lineolatus, and activity and optimal ratio of these components. By using gas chromatography–mass spectrometry (GC‐MS) and gas chromatography–electroantennographic detection (GC‐EAD), we identified three active compounds: hexyl butyrate (HB), (E)‐2‐hexenyl butyrate (E2HB), and (E)‐4‐oxo‐2‐hexenal (4‐OHE). We examined the release rate of septum and tube dispensers in a wind tunnel. In a field experiment, deletion of 4‐OHE or E2HB resulted in significant suppression of male trap catches, indicating that E2HB or 4‐OHE may be the active pheromone components. Traps baited with a blend of 4‐OHE and E2HB at 2:5, 3:4, and 4:3 caught significantly more males, suggesting that the optimal ratio of 4‐OHE and E2HB could be in the range of 1:1 to 1:2. The addition of a large amount of HB could strongly reduce the attractive activity of both virgin females and artificial lures. We also compared the attractiveness of septum lures and tube lures in field experiments. The septum lures attracted males in the first 3 days. The tube lures caught more males after 3 days and the attractive effects existed up to 5 weeks, suggesting them as a tool for long‐term monitoring and control of plant bugs.     

Effect of polyacetylenic acids from Prunella vulgaris on various plant pathogens

Aims: This study is aiming at characterizing antifungal substances from the methanol extract of Prunella vulgaris and at investigating those substances’ antifungal and antioomycete activities against various plant pathogens. Methods and Results: Two polyacetylenic acids were isolated from P. vulgaris as active principles and identified as octadeca‐9,11,13‐triynoic acid and trans‐octadec‐13‐ene‐9,11‐diynoic acid. These two compounds inhibited the growth of Magnaporthe oryzae, Rhizoctonia solani, Phytophthora infestans, Sclerotinia sclerotiorum, Fusarium oxysporum f. sp. raphani, and Phytophthora capsici. In addition, these two compounds and the wettable powder‐type formulation of an n‐hexane fraction of P. vulgaris significantly suppressed the development of rice blast, tomato late blight, wheat leaf rust, and red pepper anthracnose. Conclusions: These data show that the extract of P. vulgaris and two polyacetylenic acids possess antifungal and antioomycete activities against a broad spectrum of tested plant pathogens. Significance and Impact of the Study: This is the first report on the occurrence of octadeca‐9,11,13‐triynoic acid and trans‐octadec‐13‐ene‐9,11‐diynoic acid in P. vulgaris and their efficacy against plant diseases. The crude extract containing the two polyacetylenic acids can be used as a natural fungicide for the control of various plant diseases.     

Effects of plant quality and ant defence on herbivory rates in a neotropical ant‐plant

1. Understanding the degree to which populations and communities are limited by both bottom‐up and top‐down effects is still a major challenge for ecologists, and manipulation of plant quality, for example, can alter herbivory rates in plants. In addition, biotic defence by ants can directly influence the populations of herbivores, as demonstrated by increased rates of herbivory or increased herbivore density after ant exclusion. The aim of this study was to evaluate bottom‐up and top‐down effects on herbivory rates in a mutualistic ant‐plant. 2. In this study, the role of Azteca alfari ants as biotic defence in individuals of Cecropia pachystachya was investigated experimentally with a simultaneous manipulation of both bottom‐up (fertilisation) and top‐down (ant exclusion) factors. Four treatments were used in a fully factorial design, with 15 replicates for each treatment: (i) control plants, without manipulation; (ii) fertilised plants, ants not manipulated; (iii) unfertilised plants and excluded ants and (iv) fertilised plants and ants excluded. 3. Fertilisation increased the availability of foliar nitrogen in C. pachystachya, and herbivory rates by chewing insects were significantly higher in fertilised plants with ants excluded. 4. Herbivory, however, was more influenced by bottom‐up effects – such as the quality of the host plant – than by top‐down effects caused by ants as biotic defences, reinforcing the crucial role of leaf nutritional quality for herbivory levels experienced by plants. Conditionality in ant defence under increased nutritional quality of leaves through fertilisation might explain increased levels of herbivory in plants with higher leaf nitrogen.     

Herbivore regulation of plant abundance in aquatic ecosystems

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small‐scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta‐analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between‐taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed‐nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed‐nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top‐down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.     

Signal transduction by plant heterotrimeric G‐protein

Heterotrimeric G‐proteins are complexes that regulate important signalling pathways essential for growth and development in both plants and animals. Although plant cells are composed of the core components (Gα, Gβ and Gγ subunits) found in animal G‐proteins, the complexities of the architecture, function and signalling mechanisms of those in animals are dissimilar to those identified in some plants. Current studies on plant G‐proteins have improved knowledge of the essential physiological and agronomic properties, which when harnessed, could potentially impact global food security. Extensive studies on the molecular mechanisms underlying these properties in diverse plant species will be imperative in improving our current understanding of G‐protein signalling pathways involved in plant growth and development. The advancement of G‐protein signalling networks in distinct plant species could significantly aid in better crop development. This review summarizes current progress, novel discoveries and future prospects for this area in potential crop improvement.     

Ecological significance of light quality in optimizing plant defence

Plants balance the allocation of resources between growth and defence to optimize fitness in a competitive environment. Perception of neighbour‐detection cues, such as a low ratio of red to far‐red (R:FR) radiation, activates a suite of shade‐avoidance responses that include stem elongation and upward leaf movement, whilst simultaneously downregulating defence. This downregulation is hypothesized to benefit the plant either by mediating the growth‐defence balance in favour of growth in high plant densities or, alternatively, by mediating defence of individual leaves such that those most photosynthetically productive are best protected. To test these hypotheses, we used a 3D functional–structural plant model of Brassica nigra that mechanistically simulates the interactions between plant architecture, herbivory, and the light environment. Our results show that plant‐level defence expression is a strong determinant of plant fitness and that leaf‐level defence mediation by R:FR can provide a fitness benefit in high densities. However, optimal plant‐level defence expression does not decrease monotonically with plant density, indicating that R:FR mediation of defence alone is not enough to optimize defence between densities. Therefore, assessing the ecological significance of R:FR‐mediated defence is paramount to better understand the evolution of this physiological linkage and its implications for crop breeding.     

Recent changes in the plant composition of wetlands in the Jura Mountains

Aim

To assess vegetation changes in montane fens and wet meadows and their causes over 38 years.

Location

Wetlands, Jura Mountains (Switzerland and France).

Methods

Plots were inventoried in 1974 and re‐located in 2012 (quasi‐permanent plots) on the basis of sketches to assess changes in plant communities. The 110 plots belonged to five phytosociological alliances, two in oligotrophic fens (Caricion davallianae, Caricion fuscae) and three in wet meadows (Calthion, Molinion, Filipendulion). Changes between surveys were assessed with NMDS, and changes in species richness, Simpson diversity, species cover and frequency and the causes of these changes were evaluated by comparing ecological indicator values.

Results

Changes in species composition varied between alliances, with a general trend towards more nutrient‐rich flora with less light at ground level. Species diversity declined, with a marked decreasing trend for the typical species of each alliance. These species were partly replaced by species belonging to nitrophilous and mesophilous grasslands. However, no trend towards drier conditions was detected in these wetlands. The largest changes, with an important colonization by nitrophilous species, occurred in the Swiss sites, where grazing was banned 25 years ago. As a result of floral shifts, many plots previously belonging to fens or wet mesotrophic meadows shifted to an alliance of the wet meadows, generally Filipendulion. Moreover, communities showed a slight trend towards more thermophilous flora.

Conclusions

The investigated wetlands in the Jura Mountains have suffered mainly from eutrophication due to land‐use abandonment and N deposition, with a loss of typical species. Areas with constant land use (grazing or mowing) showed less marked changes in species composition. The most important action to conserve these wetlands is to maintain or reintroduce the traditional practices of extensive mowing and livestock grazing in the wetlands, especially in areas where they were abandoned 25 years ago. This previous land‐use change was intended to improve fen conservation, but it was obviously the wrong measure for conservation purposes.     

Facilitation allows plant coexistence in Cuban serpentine soils

Serpentine soils represent stressful habitats where plants have to cope with heavy metals, moisture limitation and low nutrient availability. We propose that facilitation is an important mechanism structuring plant communities under such stressful conditions. Facilitation has been shown to generate the spatial association of species, forming discrete vegetation patches of phylogenetically distant species. We measured these spatial and phylogenetic signatures left by facilitation in a serpentine plant community of central Cuba. Our results show that seedlings preferentially grow under plants of different species, and that adults are significantly aggregated into vegetation patches. In these patches, adults tend to co‐occur with distant relatives, ultimately forming phylogenetically diverse neighbourhoods. We discuss possible mechanisms explaining how species adapted to serpentine areas may be acting as nurses, reducing the stressful conditions for the establishment of other species.     

The importance of biological inertia in plant community resistance to invasion

Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long‐term patterns of invasions by native species. In this paper, we review literature in palaeo‐ecology, forest‐stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre‐existing community (and/or its legacy) in addition to the other biotic and abiotic factors.     

Effects of an artificial blend of host‐infested plant volatiles on plant attractiveness to parasitic wasps

For the biological control of diamondback moth (DBM) larvae in commercial greenhouses, we have previously identified a blend of volatiles that attracted Cotesia vestalis, a parasitoid of DBM larvae. Here, we tested the effects of an artificial volatile blend on the attractiveness of komatsuna plants (Japanese mustard spinach; Brassica rapa var. perviridis) to C. vestalis under greenhouse conditions. First, we showed that female C. vestalis preferred infested komatsuna plants to uninfested plants in the greenhouse. Under the same conditions, placing the artificial attractants near both infested and uninfested plants did not affect the wasps’ preference. However, when comparing infested komatsuna plants coupled with the artificial attractants with infested plants without them, significantly more female C. vestalis were attracted to the former. The possible use of artificial C. vestalis attractants for the biological control of DBM is discussed.