Thresholds for ecological responses to global change do not emerge from empirical data
Hillebrand et al. summarize 36 meta-analyses measuring more than 4,600 global change impacts on natural communities. They find that threshold transgressions were rarely detectable, either within or across meta-analyses. Instead, ecological responses were characterized mostly by progressively increasing magnitude and variance when pressure increased. Sensitivity analyses with modelled data revealed that minor variances in the response are sufficient to preclude the detection of thresholds from data, even if they are present. The simulations reinforced their contention that global change biology needs to abandon the general expectation that system properties allow defining thresholds as a way to manage nature under global change. Rather, highly variable responses, even under weak pressures, suggest that ‘safe-operating spaces’ are unlikely to be quantifiable.
Nature Ecology & Evolution
DNA damage triggers reprogramming of differentiated cells into stem cells in Physcomitrella
Gu et al. report that the transient induction of DNA strand breaks (single-strand breaks, double-strand breaks or both) in the moss Physcomitrella patens can trigger the reprogramming of differentiated leaf cells into stem cells without cell death. After intact leafy shoots (gametophores) were exposed to zeocin, an inducer of DNA strand breaks, the STEM CELL-INDUCING FACTOR 1 (STEMIN1)2 promoter was activated in some leaf cells. These cells subsequently initiated tip growth and underwent asymmetric cell divisions to form chloronema apical stem cells, which are in an earlier phase of the life cycle than leaf cells and have the ability to form new gametophores.
A molecular roadmap to the plant immune system
Bentham et al. provide a roadmap to plant immunity, with a focus on cell-surface and intracellular immune receptors. They describe how these receptors perceive signatures of pathogens and pests and initiate immune pathways. They merge existing concepts with new insights gained from recent breakthroughs on the structure and function of plant immune receptors, which have generated a shift in our understanding of cell-surface and intracellular immunity and the interplay between the two. Finally, they use our current understanding of the plant immunity as context to discuss the potential of engineering the plant immune system with the aim of bolstering plant defences against disease.
Journal of Biological Chemistry
Engineering DNA nanostructures for siRNA delivery in plants
Zhang et al. have demonstrated that DNA nanostructures can be utilized as a cargo carrier for direct siRNA delivery and gene silencing in mature plants. The size, shape, compactness and stiffness of the DNA nanostructure affect both internalization into plant cells and subsequent gene silencing efficiency. They provide a detailed protocol that can be readily adopted with standard biology benchtop equipment to generate geometrically optimized DNA nanostructures for transgene-free and force-independent siRNA delivery and gene silencing in mature plants. They further discuss how such DNA nanostructures can be rationally designed to efficiently enter plant cells and deliver cargoes to mature plants, and provide guidance for DNA nanostructure characterization, storage and use.
Genome evolution in fungal plant pathogens: looking beyond the two-speed genome model - ScienceDirect
Pathogens often deploy an arsenal of small proteins called effectors that manipulate the plant immune system and promote disease. In the post-genomics era, a major interest has been to understand what shapes the localization of effector genes in pathogen genomes. The two-speed genome model originated with the discovery of repeat-rich and gene-sparse genome compartments with an over-representation of effector-like genes in a subset of plant pathogens. These highly polymorphic genome compartments are thought to create unique niches for effector genes and facilitate rapid adaptation. Research over the past decade has revealed a number of twists to the two-speed genome model and raised questions about the universality among plant pathogens. Torres et al. critically review the foundations of the two-speed model by presenting recent work on epigenetics, transposable element dynamics, and population genetics.
Fungal Biology Reviews
Phased Secondary Small Interfering RNAs (phasiRNAs) in Plants: Their Biogenesis, Genic Sources, and Roles in Stress Responses, Development, and Reproduction
Liu et al. survey recent progress in phasiRNA biology, in particular focusing on two classes associated with male reproduction: 21-nt (accumulated early in anther ontogeny) and 24-nt (produced in somatic cells during meiosis) phasiRNAs. We describe phasiRNA biogenesis, function, and evolution, and define the unanswered questions that represent topics for future research.
Induction of Multichotomous Branching by CLAVATA Peptide in Marchantia polymorpha
Hirakawa et al. show here that in Marchantia polymorpha, treatment with MpCLE2/CLAVATA3 (CLV3) peptide resulted in the accumulation of undifferentiated cells, marked by MpYUC2 expression, in the apical meristem. Removal of MpCLE2 peptide resulted in multichotomous branching from the accumulated cells. Genetic analysis demonstrated that the CLAVATA1 (MpCLV1) receptor, but not the WUSCHEL-related HOMEOBOX (MpWOX) transcription factor, is responsible for MpCLE2 peptide signaling. In the apical meristem, MpCLV1 was expressed broadly in the central region, including the MpYUC2-positive area, whereas MpCLE2 was expressed in a largely complementary manner compared to MpYUC2, suggesting MpCLE2 mediates local cell-to-cell communication.
An excess of niche differences maximizes ecosystem functioning
Godoy et al. couple field-parameterized models of competition between 10 annual plant species with a biodiversity-functioning experiment under two contrasting environmental conditions, to study how coexistence determinants link to biodiversity effects (selection and complementarity). They find that complementarity effects positively correlate with niche differences and selection effects differences correlate with fitness differences. However, niche differences also contribute to selection effects and fitness differences to complementarity effects.
C2 photosynthesis: a promising route towards crop improvement?
C2 photosynthesis is a carbon concentrating mechanism that can increase net CO2 assimilation by capturing, concentrating and re‐assimilating CO2 released by photorespiration. Empirical and modelling studies indicate that C2 plants assimilate more carbon than C3 plants under high temperature, bright light, and low CO2 conditions. Lundgren argues that engineering C2 photosynthesis into C3 crops is a promising approach to improve photosynthetic performance under these – and temporally heterogeneous – environments, and review the modifications that may re‐create a C2 phenotype in C3 plants.
The karrikin signaling regulator SMAX1 controls Lotus japonicus root and root hair development by suppressing ethylene biosynthesis
Plant seedlings depend on efficient development of roots and root hairs for anchorage to the ground and for rapidly reaching nutrients and water for survival and growth. We found that a negative regulator of a small-molecule signaling pathway called “karrikin signaling” plays an important role in regulating root growth of the legume Lotus japonicus. Mutants of this regulator called “SMAX1” have short primary roots and strongly elongated root hairs. This phenotype is caused by enhanced ethylene biosynthesis, which in the wild type is suppressed by SMAX1. Thus, karrikin signaling regulates ethylene biosynthesis to fine-tune root development.