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New Phytologist Volume 215 Issue 2

New Phytologist

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Volume 215 Issue 2 | July 2017
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New Phytologist is an international journal offering rapid publication of high quality, original research in plant science. Covering four sections - Physiology & Development, Environment, Interaction and Evolution - articles cover topics that range from intracellular processes through to global environmental change. Cross-disciplinary approaches are particularly encouraged and we recognize that techniques from molecular and cell biology, and functional genomics through to modelling and system-based approaches will be applied across the whole spectrum of plant science.

Highlights

Venuleo, Raven & Giordano (2017), Figure 1

Intraspecific chemical communication in microalgae

The relevance of infochemicals in the relationships between organisms is emerging as a fundamental aspect of aquatic ecology. Exchanges of chemical cues are likely to occur not only between organisms of different species, but also between conspecific individuals. Especially intriguing is the investigation of chemical communication in microalgae, because of the relevance of these organisms for global primary production and their key role in trophic webs. Intraspecific communication between algae has been investigated mostly in relation to sexuality and mating. The literature also contains information on other types of intraspecific chemical communication that have not always been explicitly tagged as ways to communicate to conspecifics. However, the proposed role of certain compounds as intraspecific infochemicals appears questionable. In this article, we make use of this plethora of information to describe the various instances of intraspecific chemical communication between conspecific microalgae and to identify the common traits and ecological significance of intraspecific communication. We also discuss the evolutionary implications of intraspecific chemical communication and the mechanisms by which it can be inherited. A special focus is the genetic diversity among conspecific algae, including the possibility that genetic diversity is an absolute requirement for intraspecific chemical communication.



Lenton & Daines (2017), Figure 2

Matworld – the biogeochemical effects of early life on land

There is growing evidence that life has been on land for billions of years. Microbial mats fuelled by oxygenic photosynthesis were probably present in terrestrial habitats from c. 3.0 billion yr ago (Ga) onwards, creating localized ‘oxygen oases’ under a reducing atmosphere, which left a characteristic oxidative weathering signal. After the Great Oxidation c. 2.4 Ga, the now oxidizing atmosphere masked that redox signal, but ancient soils record the mobilization of phosphorus and other elements by organic acids in weathering profiles. Evidence for Neoproterozoic ‘greening of the land’ and intensification of weathering c. 0.85–0.54 Ga is currently equivocal. However, the mid-Palaeozoic c. 0.45–0.4 Ga shows global atmospheric changes consistent with increased terrestrial productivity and intensified weathering by the first land plants.



Hetherington & Dolan (2017) Figure 3

The evolution of lycopsid rooting structures: conservatism and disparity

The evolution of rooting structures was a crucial event in Earth's history, increasing the ability of plants to extract water, mine for nutrients and anchor above-ground shoot systems. Fossil evidence indicates that roots evolved at least twice among vascular plants, in the euphyllophytes and independently in the lycophytes. Here, we review the anatomy and evolution of lycopsid rooting structures. Highlighting recent discoveries made with fossils we suggest that the evolution of lycopsid rooting structures displays two contrasting patterns – conservatism and disparity. The structures termed roots have remained structurally similar despite hundreds of millions of years of evolution – an example of remarkable conservatism. By contrast, and over the same time period, the organs that give rise to roots have diversified, resulting in the evolution of numerous novel and disparate organs.



Harrison (2017), Figure 1

Auxin transport in the evolution of branching forms

Branching is one of the most striking aspects of land plant architecture, affecting resource acquisition and yield. Polar auxin transport by PIN proteins is a primary determinant of flowering plant branching patterns regulating both branch initiation and branch outgrowth. Several lines of experimental evidence suggest that PIN-mediated polar auxin transport is a conserved regulator of branching in vascular plant sporophytes. However, the mechanisms of branching and auxin transport and relationships between the two are not well known outside the flowering plants, and the paradigm for PIN-regulated branching in flowering plants does not fit bryophyte gametophytes. The evidence reviewed here suggests that divergent auxin transport routes contributed to the diversification of branching forms in distinct land plant lineages.



Boyce, Fan & Zwieniecki (2017), Figure 1

Did trees grow up to the light, up to the wind, or down to the water? How modern high productivity colors perception of early plant evolution

Flowering plants can be far more productive than other living land plants. Evidence is reviewed that productivity would have been uniformly lower and less CO2-responsive before angiosperm evolution, particularly during the early evolution of vascular plants and forests in the Devonian and Carboniferous. This introduces important challenges because paleoecological interpretations have been rooted in understanding of modern angiosperm-dominated ecosystems. One key example is tree evolution: although often thought to reflect competition for light, light limitation is unlikely for plants with such low photosynthetic potential. Instead, during this early evolution, the capacities of trees for enhanced propagule dispersal, greater leaf area, and deep-rooting access to nutrients and the water table are all deemed more fundamental potential drivers than light.



Koskella et al. (2017), Figure 1

A signature of tree health? Shifts in the microbiome and the ecological drivers of horse chestnut bleeding canker disease

  • Host susceptibility to pathogens can be shaped by genetic, ecological, and evolutionary factors. The ability to predict the spread of disease therefore requires an integrated understanding of these factors, including effects of pests on pathogen growth and competition between pathogens and commensal microbiota for host resources. We examined interactions between the leaf-mining moth Cameraria ohridella, the bacterial causal agent of bleeding canker disease Pseudomonas syringae pv aesculi, and the bark-associated microbiota of horse chestnut (Aesculus hippocastanum) trees.
  • Through surveys of > 900 trees from 60 sites in the UK, we tested for ecological or life history predictors of leaf miner infestation, bleeding canker, or coinfection. Using culture-independent sequencing, we then compared the bark microbiomes from 46 trees to measure the association between microbiome composition and key ecological variables, including the severity of disease.
  • Both pest and pathogen were found to respond to tree characteristics, but neither explained damage inflicted by the other. However, we found a clear loss of microbial diversity and associated shift in microbiome composition of trees as a function of disease.
  • These results show a link between bark-associated microbiota and tree health that introduces the intriguing possibility that tree microbiota play key roles in the spread of disease.


Smith, et al. (2017), Figure 1

Growing evidence for facultative biotrophy in saprotrophic fungi: data from microcosm tests with 201 species of wood-decay basidiomycetes

  • Ectomycorrhizal (ECM) symbioses have evolved a minimum of 78 times independently from saprotrophic lineages, indicating the potential for functional overlap between ECM and saprotrophic fungi. ECM fungi have the capacity to decompose organic matter, and although there is increasing evidence that some saprotrophic fungi exhibit the capacity to enter into facultative biotrophic relationships with plant roots without causing disease symptoms, this subject is still not well studied.
  • In order to determine the extent of biotrophic capacity in saprotrophic wood-decay fungi and which systems may be useful models, we investigated the colonization of conifer seedling roots in vitro using an array of 201 basidiomycete wood-decay fungi. Microtome sectioning, differential staining and fluorescence microscopy were used to visualize patterns of root colonization in microcosm systems containing Picea abies or Pinus sylvestris seedlings and each saprotrophic fungus.
  • Thirty-four (16.9%) of the tested fungal species colonized the roots of at least one tree species. Two fungal species showed formation of a mantle and one showed Hartig net-like structures. These features suggest the possibility of an active functional symbiosis between fungus and plant.
  • The data indicate that the capacity for facultative biotrophic relationships in free-living saprotrophic basidiomycetes may be greater than previously supposed.