Functional analysis of endo‐1,4‐β‐glucanases in response to Botrytis cinerea and Pseudomonas syringae reveals their involvement in plant–pathogen interactions

Plant cell wall modification is a critical component in stress responses. Endo‐1,4‐β‐glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence‐signalling network. A study of a set of Arabidopsis EG T‐DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant–pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant–pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.     

Insulin‐like growth factors and their potential role in cardiac epigenetics

Cardiovascular disease (CVD) constitutes a major public health threat worldwide, accounting for 17.3 million deaths annually. Heart disease and stroke account for the majority of healthcare costs in the developed world. While much has been accomplished in understanding the pathophysiology, molecular biology and genetics underlying the diagnosis and treatment of CVD, we know less about the role of epigenetics and their molecular determinants. The impact of environmental changes and epigenetics in CVD is now emerging as critically important in understanding the origin of disease and the development of new therapeutic approaches to prevention and treatment. This review focuses on the emerging role of epigenetics mediated by insulin like‐growth factors‐I and ‐II in major CVDs such as heart failure, cardiac hypertrophy and diabetes.     

Strong specificity in the interaction between parasitoids and symbiont‐protected hosts

Coevolution between hosts and parasites may promote the maintenance of genetic variation in both antagonists by negative frequency‐dependence if the host–parasite interaction is genotype‐specific. Here we tested for specificity in the interaction between parasitoids (Lysiphlebus fabarum) and aphid hosts (Aphis fabae) that are protected by a heritable defensive endosymbiont, the γ‐proteobacterium Hamiltonella defensa. Previous studies reported a lack of genotype specificity between unprotected aphids and parasitoids, but suggested that symbiont‐conferred resistance might exhibit a higher degree of specificity. Indeed, in addition to ample variation in host resistance as well as parasitoid infectivity, we found a strong aphid clone‐by‐parasitoid line interaction on the rates of successful parasitism. This genotype specificity appears to be mediated by H. defensa, highlighting the important role that endosymbionts can play in host–parasite coevolution.     

The ROS‐induced cytotoxicity of ascorbate is attenuated by hypoxia and HIF‐1alpha in the NCI60 cancer cell lines

Intravenous application of high‐dose ascorbate is used in complementary palliative medicine to treat cancer patients. Pharmacological doses of ascorbate in the mM range induce cytotoxicity in cancer cells mediated by reactive oxygen species (ROS), namely hydrogen peroxide and ascorbyl radicals. However, little is known about intrinsic or extrinsic factors modulating this ascorbate‐mediated cytotoxicity. Under normoxia and hypoxia, ascorbate IC₅₀ values were determined on the NCI60 cancer cells. The cell cycle, the influence of cobalt chloride‐induced hypoxia‐inducible factor‐1α (HIF‐1α) and the glucose transporter 1 (GLUT‐1) expression (a pro‐survival HIF‐1α‐downstream‐target) were analysed after ascorbate exposure under normoxic and hypoxic conditions. The amount of ascorbyl radicals increased with rising serum concentrations. Hypoxia (0.1% O₂) globally increased the IC₅₀ of ascorbate in the 60 cancer cell lines from 4.5 ± 3.6 mM to 10.1 ± 5.9 mM (2.2‐fold increase, P < 0.001, Mann–Whitney t‐test), thus inducing cellular resistance towards ascorbate. This ascorbate resistance depended on HIF‐1α‐signalling, but did not correlate with cell line‐specific expression of the ascorbate transporter GLUT‐1. However, under normoxic and hypoxic conditions, ascorbate treatment at the individual IC₅₀ reduced the expression of GLUT‐1 in the cancer cells. Our data show a ROS‐induced, HIF‐1α‐ and O₂‐dependent cytotoxicity of ascorbate on 60 different cancer cells. This suggests that for clinical application, cancer patients should additionally be oxygenized to increase the cytotoxic efficacy of ascorbate.     

Comparative metabolic profiling between desiccation‐sensitive and desiccation‐tolerant species of Selaginella reveals insights into the resurrection trait

Spike mosses (Selaginellaceae) represent an ancient lineage of vascular plants in which some species have evolved desiccation tolerance (DT). A sister‐group contrast to reveal the metabolic basis of DT was conducted between a desiccation‐tolerant species, Selaginella lepidophylla, and a desiccation‐sensitive species, Selaginella moellendorffii, at 100% relative water content (RWC) and 50% RWC using non‐biased, global metabolomics profiling technology, based on GC/MS and UHLC/MS/MS² platforms. A total of 301 metabolites, including 170 named (56.5%) and 131 (43.5%) unnamed compounds, were characterized across both species. S. lepidophylla retained significantly higher abundances of sucrose, mono‐ and polysaccharides, and sugar alcohols than did S. moellendorffii. Aromatic amino acids, the well‐known osmoprotectant betaine and flavonoids were also more abundant in S. lepidophylla. Notably, levels of γ‐glutamyl amino acid, linked with glutathione metabolism in the detoxification of reactive oxygen species, and with possible nitrogen remobilization following rehydration, were markedly higher in S. lepidophylla. Markers for lipoxygenase activity were also greater in S. lepidophylla, especially at 50% RWC. S. moellendorffii contained more than twice the number of unnamed compounds, with only a slightly greater abundance than in S. lepidophylla. In contrast, S. lepidophylla contained 14 unnamed compounds of fivefold or greater abundance than in S. moellendorffii, suggesting that these compounds might play critical roles in DT. Overall, S. lepidophylla appears poised to tolerate desiccation in a constitutive manner using a wide range of metabolites with some inducible components, whereas S. moellendorffii mounts only limited metabolic responses to dehydration stress.     

Isolation of five rice nonendosperm tissue‐expressed promoters and evaluation of their activities in transgenic rice

Using promoters expressed in nonendosperm tissues to activate target genes in specific plant tissues or organs with very limited expression in the endosperm is an attractive approach in crop transgenic engineering. In this article, five putative nonendosperm tissue‐expressed promoters were cloned from the rice genome and designated P_OsNETE1, P_OsNETE2, P_OsNETE3, P_OsNETE4 and P_OsNETE5. By qualitatively and quantitatively examining GUSplus reporter gene expression in transgenic rice plants, P_OsNETE1‐P_OsNETE5 were all found to be active in the roots, leaves, stems, sheaths and panicles but not in the endosperm of plants at different developmental stages. In addition, P_OsNETE2, P_OsNETE4 and P_OsNETE5 were also inactive in rice embryos. Among these promoters, P_OsNETE4 and P_OsNETE5 exhibited higher activities in all of the tested tissues, and their activities in stems, leaves, roots and sheaths were higher than or comparable to those of the rice Actin1 promoter. We also progressively monitored the activities of P_OsNETE1‐P_OsNETE5 in two generations of single‐copy lines and found that these promoters were stably expressed between generations. Transgenic rice was produced using P_OsNETE4 and P_OsNETE5 to drive a modified Bt gene, mCry1Ab. Bt protein expressed in the tested plants ranged from 1769.4 to 4428.8 ng/g fresh leaves, whereas Bt protein was barely detected in the endosperm. Overall, our study identified five novel nonendosperm tissue‐expressed promoters that might be suitable for rice genetic engineering and might reduce potential social concern regarding the safety of GMO crops.     

Sub‐lethal UV‐C radiation induces callose,hydrogen peroxide and defence‐related gene expression in Arabidopsis thaliana

Exposure of plants to UV‐C irradiation induces gene expression and cellular responses that are commonly associated with wounding and pathogen defence, and in some cases can lead to increased resistance against pathogen infection. We examined, at a physiological, molecular and biochemical level, the effects of and responses to, sub‐lethal UV‐C exposure on Arabidopsis plants when irradiated with increasing dosages of UV‐C radiation. Following UV‐C exposure plants had reduced leaf areas over time, with the severity of reduction increasing with dosage. Severe morphological changes that included leaf glazing, bronzing and curling were found to occur in plants treated with the 1000 J·m^?2 dosage. Extensive damage to the mesophyll was observed, and cell death occurred in both a dosage‐ and time‐dependent manner. Analysis of H₂O₂ activity and the pathogen defence marker genes PR1 and PDF1.2 demonstrated induction of these defence‐related responses at each UV‐C dosage tested. Interestingly, in response to UV‐C irradiation the production of callose (β‐1,3‐glucan) was identified at all dosages examined. Together, these results show plant responses to UV‐C irradiation at much lower doses than have previously been reported, and that there is potential for the use of UV‐C as an inducer of plant defence.     

Nonlinear frequency‐dependent selection promotes long‐term coexistence between bacteria species

Negative frequency‐dependent selection (NFDS) is an important mechanism for species coexistence and for the maintenance of genetic polymorphism. Long‐term coexistence nevertheless requires NFDS interactions to be resilient to further evolution of the interacting species or genotypes. For closely related genotypes, NFDS interactions have been shown to be preserved through successive rounds of evolution in coexisting lineages. On the contrary, the evolution of NFDS interactions between distantly related species has received less attention. Here, we tracked the co‐evolution of Escherichia coli and Citrobacter freundii that initially differ in their ecological characteristics. We showed that these two bacterial species engaged in an NFDS interaction particularly resilient to further evolution: despite a very strong asymmetric rate of adaptation, their coexistence was maintained owing to an NFDS pattern where fitness increases steeply as the frequency decreases towards zero. Using a model, we showed how and why such NFDS pattern can emerge. These findings provide a robust explanation for the long‐term maintenance of species at very low frequencies.