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New Phytologist Volume 214 Issue 1

New Phytologist

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Volume 214 Issue 2 | May 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

Gessler et al (2017) Figure 1

Tansley insight: Nutrients, drought-induced tree mortality and recovery

Global forests are experiencing rising temperatures and more severe droughts, with consistently dire forecasts for negative future impacts. Current research on the physiological mechanisms underlying drought impacts is focused on the water- and carbon-associated mechanisms. The role of nutrients is notably missing from this research agenda. Here, we investigate what role, if any, forest nutrition plays for survival and recovery of forests during and after drought. High nutrient availability may play a detrimental role in drought survival due to preferential biomass allocation aboveground that (1) predispose plants to hydraulic constraints limiting photosynthesis and promoting hydraulic failure, (2) increases carbon costs during periods of carbon starvation, and (3) promote biotic attack due to low tissue carbon: nitrogen (C : N). When nutrient uptake occurs during drought, high nutrient availability can increase water use efficiency thus minimizing negative feedbacks between carbon and nutrient balance. Nutrients are released after drought ceases, which might promote faster recovery but the temporal dynamics of microbial immobilization and nutrient leaching have a significant impact on nutrient availability. We provide a framework for understanding nutrient impacts on drought survival that allows a more complete analysis of forest ecosystem responses.


Curie and Mari (2017) Figure 1

Tansley insight: New routes for plant iron mining

Plant iron (Fe) uptake relies to a large extent on the capacity of cells to control and extract Fe pools safely conserved in extracytoplasmic environments such as the apoplast and vacuoles, at least as much as on the transport machinery nested in plasma membranes. Recent studies on root and embryo Fe nutrition support this assertion and show that the root Fe-deficiency response also includes the dynamic use of a large Fe reservoir bound to cell wall components in the root apoplast, secretion in the apoplast of phenolic compounds of the coumarin family, which solubilize Fe in calcareous soils, and inhibition of suberization of endodermal cells in order to allow apoplastic and transcellular radial transport of Fe. All of these responses are regulated by the stress hormones ethylene and abscisic acid (ABA), suggesting an integrated strategy within the root to adapt to Fe shortage. For its nutrition, the embryo has developed both an original uptake mechanism, in which ascorbate is effluxed to chemically reduce Fe3+ to the transport-competent Fe2+ form, and an efficient strategy to control utilization of a large Fe pool in vacuoles. This review will attempt to summarize exciting new insights into the diverse routes that Fe takes to feed plant tissues.


Rouxel and Balesdent. (2017) Figure 3

Tansley insight: Avirulence effectors in Brassica crops

In agricultural systems, major (R) genes for resistance in plants exert strong selection pressure on cognate/corresponding avirulence effector genes of phytopathogens. However, a complex interplay often exists between trade-offs linked to effector function and the need to escape R gene recognition. Here, using the Leptosphaeria maculans–oilseed rape pathosystem we review evolution of effectors submitted to multiple resistance gene selection. Characteristics of this pathosystem include a crop in which resistance genes have been deployed intensively resulting in 'boom and bust' cycles; a fungal pathogen with a high adaptive potential in which seven avirulence genes are cloned and for which population surveys have been coupled with molecular analysis of events responsible for virulence. The mode of evolution of avirulence genes, all located in dispensable parts of the 'two-speed' genome, is a highly dynamic gene-specific process. In some instances, avirulence genes are readily deleted under selection. However, others, even when located in the most plastic genome regions, undergo only limited point mutations or their avirulence phenotype is 'camouflaged' by another avirulence gene. Thus, while hundreds of effector genes are present, some effectors are likely to have an important and nonredundant function, suggesting functional redundancy and dispensability of effectors might not be the rule.


Barker et al. (2017) Figure 1

Tansley insight: Ca2+ signaling in mycorrhizal endosymbiosis

Root endosymbioses are beneficial associations formed between terrestrial plants and either bacterial or fungal micro-organisms. A common feature of these intracellular symbioses is the requirement for mutual recognition between the two partners before host-regulated microbial entry. As part of this molecular dialogue, symbiosis-specific microbial factors set in motion a highly conserved plant signal transduction pathway, of which a central component is the activation of sustained nuclear Ca2+ oscillations in target cells of the host epidermis. Here, we focus on recent findings concerning this crucial Ca2+-dependent signalling step for endosymbiotic associations involving either arbuscular mycorrhizal fungi or nitrogen-fixing Frankia actinomycetes, and in particular how this knowledge is contributing to the identification of the respective microbial factors.


Atkinson et al. (2017) Figure 4

Rubisco small subunits from the unicellular green alga Chlamydomonas complement Rubisco-deficient mutants of Arabidopsis

  • Introducing components of algal carbon concentrating mechanisms (CCMs) into higher plant chloroplasts could increase photosynthetic productivity. A key component is the Rubisco-containing pyrenoid that is needed to minimise CO2 retro-diffusion for CCM operating efficiency.
  • Rubisco in Arabidopsis was re-engineered to incorporate sequence elements that are thought to be essential for recruitment of Rubisco to the pyrenoid, namely the algal Rubisco small subunit (SSU, encoded by rbcS) or only the surface-exposed algal SSU α-helices.
  • Leaves of Arabidopsis rbcs mutants expressing 'pyrenoid-competent' chimeric Arabidopsis SSUs containing the SSU α-helices from Chlamydomonas reinhardtii can form hybrid Rubisco complexes with catalytic properties similar to those of native Rubisco, suggesting that the α-helices are catalytically neutral.
  • The growth and photosynthetic performance of complemented Arabidopsis rbcs mutants producing near wild-type levels of the hybrid Rubisco were similar to those of wild-type controls. Arabidopsis rbcs mutants expressing a Chlamydomonas SSU differed from wild-type plants with respect to Rubisco catalysis, photosynthesis and growth. This confirms a role for the SSU in influencing Rubisco catalytic properties.