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New Phytologist Volume 215 Issue 3

New Phytologist

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Volume 215 Issue 3 | August 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

Gimeno et al. (2017) Figure 1

Bryophyte gas-exchange dynamics along varying hydration status reveal a significant carbonyl sulphide (COS) sink in the dark and COS source in the light

  • Carbonyl sulphide (COS) is a potential tracer of gross primary productivity (GPP), assuming a unidirectional COS flux into the vegetation that scales with GPP. However, carbonic anhydrase (CA), the enzyme that hydrolyses COS, is expected to be light independent, and thus plants without stomata should continue to take up COS in the dark.
  • We measured net CO2 (AC) and COS (AS) uptake rates from two astomatous bryophytes at different relative water contents (RWCs), COS concentrations, temperatures and light intensities.
  • We found large AS in the dark, indicating that CA activity continues without photosynthesis. More surprisingly, we found a nonzero COS compensation point in light and dark conditions, indicating a temperature-driven COS source with a Q10 (fractional change for a 10°C temperature increase) of 3.7. This resulted in greater AS in the dark than in the light at similar RWC. The processes underlying such COS emissions remain unknown.
  • Our results suggest that ecosystems dominated by bryophytes might be strong atmospheric sinks of COS at night and weaker sinks or even sources of COS during daytime. Biotic COS production in bryophytes could result from symbiotic fungal and bacterial partners that could also be found on vascular plants.


Xu et al. (2017), Figure 1

OsHAC4 is critical for arsenate tolerance and regulates arsenic accumulation in rice

  • Soil contamination with arsenic (As) can cause phytotoxicity and elevated As accumulation in rice grain. Here, we used a forward genetics approach to investigate the mechanism of arsenate (As(V)) tolerance and accumulation in rice.
  • A rice mutant hypersensitive to As(V), but not to As(III), was isolated. Genomic resequencing and complementation tests were used to identify the causal gene. The function of the gene, its expression pattern and subcellular localization were characterized.
  • OsHAC4 is the causal gene for the As(V)-hypersensitive phenotype. The gene encodes a rhodanase-like protein that shows As(V) reductase activity when expressed in Escherichia coli. OsHAC4 was highly expressed in roots and was induced by As(V). In OsHAC4pro-GUStransgenic plants, the gene was expressed exclusively in the root epidermis and exodermis. OsHAC4-eGFP was localized in the cytoplasm and the nucleus. Mutation in OsHAC4 resulted in decreased As(V) reduction in roots, decreased As(III) efflux to the external medium and markedly increased As accumulation in rice shoots. Overexpression of OsHAC4 increased As(V) tolerance and decreased As accumulation in rice plants.
  • OsHAC4 is an As(V) reductase that is critical for As(V) detoxification and for the control of As accumulation in rice. As(V) reduction, followed by As(III) efflux, is an important mechanism of As(V) detoxification.


Austen et al. (2017) Figure 1

Explaining the apparent paradox of persistent selection for early flowering

Decades of observation in natural plant populations have revealed pervasive phenotypic selection for early flowering onset. This consistent pattern seems at odds with life-history theory, which predicts stabilizing selection on age and size at reproduction. Why is selection for later flowering rare? Moreover, extensive evidence demonstrates that flowering time can and does evolve. What maintains ongoing directional selection for early flowering? Several non-mutually exclusive processes can help to reconcile the apparent paradox of selection for early flowering. We outline four: selection through other fitness components may counter observed fecundity selection for early flowering; asymmetry in the flowering-time–fitness function may make selection for later flowering hard to detect; flowering time and fitness may be condition-dependent; and selection on flowering duration is largely unaccounted for. In this Viewpoint, we develop these four mechanisms, and highlight areas where further study will improve our understanding of flowering-time evolution.



Kerfeld et al. (2017), Figure 1

Structure, function and evolution of the cyanobacterial orange carotenoid protein and its homologs

The orange carotenoid protein (OCP) is a water-soluble, photoactive protein involved in thermal dissipation of excess energy absorbed by the light-harvesting phycobilisomes (PBS) in cyanobacteria. The OCP is structurally and functionally modular, consisting of a sensor domain, an effector domain and a keto-carotenoid. On photoactivation, the OCP converts from a stable orange form, OCPO, to a red form, OCPR. Activation is accompanied by a translocation of the carotenoid deeper into the effector domain. The increasing availability of cyanobacterial genomes has enabled the identification of new OCP families (OCP1, OCP2, OCPX). The fluorescence recovery protein (FRP) detaches OCP1 from the PBS core, accelerating its back-conversion to OCPO; by contrast, other OCP families are not regulated by FRP. N-terminal domain homologs, the helical carotenoid proteins (HCPs), have been found among diverse cyanobacteria, occurring as multiple paralogous groups, with two representatives exhibiting strong singlet oxygen (1O2) quenching (HCP2, HCP3) and another capable of dissipating PBS excitation (HCP4). Crystal structures are presently available for OCP1 and HCP1, and models of other HCP subtypes can be readily produced as a result of strong sequence conservation, providing new insights into the determinants of carotenoid binding and 1O2 quenching.



Minina, Moschou & Bozhkov (2017) Figure 1

Limited and digestive proteolysis: crosstalk between evolutionary conserved pathways

Proteases can either digest target proteins or perform the so-called ‘limited proteolysis’ by cleaving polypeptide chains at specific site(s). Autophagy and the ubiquitin–proteasome system (UPS) are two main mechanisms carrying out digestive proteolysis. While the net outcome of digestive proteolysis is the loss of function of protein substrates, limited proteolysis can additionally lead to gain or switch of function. Recent evidence of crosstalk between autophagy, UPS and limited proteolysis indicates that these pathways are parts of the same proteolytic nexus. Here, we focus on three emerging themes within this area: limited proteolysis as a mechanism modulating autophagy; interplay between autophagy and UPS, including autophagic degradation of proteasomes (proteophagy); and specificity of protein degradation during bulk autophagy.



Kanazawa & Ueda (2017) Figure 1

Exocytic trafficking pathways in plants: why and how they are redirected

The membrane trafficking system is responsible for precise transportation and localization of proteins, lipids, and polysaccharides among single membrane-bound organelles, the plasma membrane, and the extracellular space. While the exocytic trafficking pathway is considered to be a default transport pathway in many organisms, including land plants, research has shown that evolutionary processes led to an increase in the number of machinery components involved in the plant exocytic pathway. This study provides an overview of the diversification of exocytic trafficking pathways in plants, which mediate the formation and maintenance of cell polarity, interaction with symbiotic and pathogenic microbes, and cytokinesis. To fulfill these functions, distinct strategies have been employed to reroute secretory/exocytic transport during land plant evolution.