A transgenic approach to understanding the influence of carbonic anhydrase on C18OO discrimination during C4 photosynthesis

The oxygen isotope composition of atmospheric CO(2) is an important signal that helps distinguish between ecosystem photosynthetic and respiratory processes. In C(4) plants the carbonic anhydrase (CA)-catalyzed interconversion of CO(2) and bicarbonate (HCO(3)(-)) is an essential first reaction for C(4) photosynthesis but also plays an important role in the CO(2)-H(2)O exchange of oxygen as it enhances the rate of isotopic equilibrium between CO(2) and water. The C(4) dicot Flaveria bidentis containing genetically reduced levels of leaf CA (CA(leaf)) has been used to test whether changing leaf CA activity influences online measurements of C(18)OO discrimination (Delta(18)O) and the proportion of CO(2) in isotopic equilibrium with leaf water at the site of oxygen exchange (theta). The Delta(18)O in wild-type F. bidentis, which contains high levels of CA relative to the rates of net CO(2) assimilation, was less than predicted by models of Delta(18)O. Additionally, Delta(18)O was sensitive to small decreases in CA(leaf). However, reduced CA activity in F. bidentis had little effect on net CO(2) assimilation, transpiration rates (E), and stomatal conductance (g(s)) until CA levels were less than 20% of wild type. The values of theta determined from measurements of Delta(18)O and the (18)O isotopic composition of leaf water at the site of evaporation (delta(e)) were low in the wild-type F. bidentis and decreased in transgenic plants with reduced levels of CA activity. Measured values of theta were always significantly lower than the values of theta predicted from in vitro CA activity and gas exchange. The data presented here indicates that CA content in a C(4) leaf may not represent the CA activity associated with the CO(2)-H(2)O oxygen exchange and therefore may not be a good predictor of theta during C(4) photosynthesis. Furthermore, uncertainties in the isotopic composition of water at the site of exchange may also limit the ability to accurately predict theta in C(4) plants.     

Global human security in the post–COVID-19 era: The rising role of East Asia

Kenji Shibuya and coauthors discuss the potential contribution of East Asian countries to global health in the light of COVID-19.

Summary points

• East Asia, comprising the 10 ASEAN countries, China, Japan, and the countries of the Korean peninsula, has achieved comparatively good outcomes during the ongoing Coronavirus Disease 2019 (COVID-19) pandemic.
• This can be explained by sociological imprinting of and learning from past outbreaks, as well as competent governance.
• Concomitantly, East Asian nations have also been expanding capacity in global health development and diplomatic outreach, although there is as yet no coherent regional bloc vision, shared strategy, or a common set of operating principles, thus limiting synergistic impact.
• We believe that concrete next steps to bolster cooperation and extend influence could include the establishment of an East Asian Center for Disease Control, joint work in health and human security by the Asian Development Bank (ADB) and Asian Infrastructure and Investment Bank, and a region-wide research funding programme.
• Much, however, depends on evolving geopolitics writ large, notably the instability and reorientation of global alliances, which have the potential to adversely affect relations between neighbouring East Asian member states.
• Health diplomacy for global human security has the potential to become a stabilising influence and can be a topic around which all actors can more comfortably rally.

While the constituent countries of East Asia share common elements of history and culture, there is great diversity and rapid transition in social systems, economic development, demography, and epidemiological profiles (S1 Table). These factors fundamentally lead to the full range of major global health challenges, including those concerning epidemics and pandemics of novel and reemerging pathogens.Here, in the light of Coronavirus Disease 2019 (COVID-19), we discuss East Asia’s experience in this and past major outbreaks, its capacity and willingness to share best practice and support global health development, and the regional bloc’s potential in reshaping the global architecture for human security.Geographically and ethnoculturally, East Asia has conventionally referred to the region comprising China, Japan, Republic of Korea (South Korea), Democratic People’s Republic of Korea (North Korea), and Mongolia. More recently, the term has been broadened to encompass Southeast Asia (viz the 10 member states of ASEAN, the Association of South East Asian Nations), largely due to expanded regional economic cooperation and latterly for geopolitical reasons.     

Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision

Ethylene biosynthesis in leaf discs of tobacco ( Nicotiana tabacum L. cv. Xanthi), as measured by the conversion of L-[3,4-¹⁴C]-methionine to ¹⁴C₂H₄, was markedly inhibited by exogenous ethylene. This inhibition was accompanied by a decrease in total (free + conjugated) content of 1-aminocyclopropane-1-carboxylic acid (ACC), most of which appeared in its conjugated inactive form. The autoinhibitory effect of ethylene was reversible and could be relieved by Ag⁺. The Ag⁺-treated leaf discs, with or without ethylene, contained only free ACC at an increased level. The results suggest that in tobacco leaves, the autoinhibition of ethylene production resulted from reduction in the availability of free ACC, through both suppression of ACC formation and increased ACC conjugation.     

Experimental analysis of co‐evolution within protein complexes: The yeast exosome as a model

Extensive bioinformatics analysis suggests that the stability and function of protein complexes are maintained throughout evolution by coordinated changes (co‐evolution) of complex subunits. Yet, relatively little is known regarding the actual dynamics of such processes and the functional implications of co‐evolution within protein complexes, since most of the bioinformatics predictions were not analyzed experimentally. Here, we describe a systematic experimental approach that allows a step‐by‐step observation of the co‐evolution process in protein complexes. The exosome complex, an essential complex exhibiting a 3′→5′ RNA degradation activity, served as a model system. In this study, we show that exosome subunits diverged very early during fungal evolution. Interestingly, we found that despite significant differences in conservation between Rrp41 and Mtr3 both subunits exhibit similar divergence pattern and co‐evolutionary behavior through fungi evolution. Activity analysis of mutated exosomes exposes another layer of co‐evolution between the core subunits and RNA substrates. Overall, our approach allows the experimental analysis of co‐evolution within protein complexes and together with bioinformatics analysis can significantly deepen our understanding of the evolution of these complexes. Proteins 2013; 81:1997–2006. © 2013 Wiley Periodicals, Inc.     

Extensive metabolic cross-talk in melon fruit revealed by spatial and developmental combinatorial metabolomics

? Variations in tissue development and spatial composition have a major impact on the nutritional and organoleptic qualities of ripe fleshy fruit, including melon (Cucumis melo). To gain a deeper insight into the mechanisms involved in these changes, we identified key metabolites for rational food quality design. ? The metabolome, volatiles and mineral elements were profiled employing an unprecedented range of complementary analytical technologies. Fruits were followed at a number of time points during the final ripening process and tissues were collected across the fruit flesh from rind to seed cavity. Approximately 2000 metabolite signatures and 15 mineral elements were determined in an assessment of temporal and spatial melon fruit development. ? This study design enabled the identification of: coregulated hubs (including aspartic acid, 2-isopropylmalic acid, β-carotene, phytoene and dihydropseudoionone) in metabolic association networks; global patterns of coordinated compositional changes; and links of primary and secondary metabolism to key mineral and volatile fruit complements. ? The results reveal the extent of metabolic interactions relevant to ripe fruit quality and thus have enabled the identification of essential candidate metabolites for the high-throughput screening of melon breeding populations for targeted breeding programmes aimed at nutrition and flavour improvement.     

Mesophyll CO2 conductance and leakiness are not responsive to short‐ and long‐term soil water limitations in the C4 plant Sorghum bicolor

Breeding economically important C₄ crops for enhanced whole‐plant water‐use efficiency (WUE_plant) is needed for sustainable agriculture. WUE_plant is a complex trait and an efficient phenotyping method that reports on components of WUE_plant, such as intrinsic water‐use efficiency (WUE_i, the rate of leaf CO₂ assimilation relative to water loss via stomatal conductance), is needed. In C₄ plants, theoretical models suggest that leaf carbon isotope composition (δ¹³C), when the efficiency of the CO₂‐concentrating mechanism (leakiness, ?) remains constant, can be used to screen for WUE_i. The limited information about how ? responds to water limitations confines the application of δ¹³C for WUE_i screening of C₄ crops. The current research aimed to test the response of ? to short‐ or long‐term moderate water limitations, and the relationship of δ¹³C with WUE_i and WUE_plant, by addressing potential mesophyll CO₂ conductance (g_m) and biochemical limitations in the C₄ plant Sorghum bicolor. We demonstrate that g_m and ? are not responsive to short‐ or long‐term water limitations. Additionally, δ¹³C was not correlated with gas‐exchange estimates of WUE_i under short‐ and long‐term water limitations, but showed a significant negative relationship with WUE_plant. The observed association between the δ¹³C and WUE_plant suggests an intrinsic link of δ¹³C with WUE_i in this C₄ plant, and can potentially be used as a screening tool for WUE_plant in sorghum.     

Multisensory Control of Multimodal Behavior: Do the Legs Know What the Tongue Is Doing?

Understanding of adaptive behavior requires the precisely controlled presentation of multisensory stimuli combined with simultaneous measurement of multiple behavioral modalities. Hence, we developed a virtual reality apparatus that allows for simultaneous measurement of reward checking, a commonly used measure in associative learning paradigms, and navigational behavior, along with precisely controlled presentation of visual, auditory and reward stimuli. Rats performed a virtual spatial navigation task analogous to the Morris maze where only distal visual or auditory cues provided spatial information. Spatial navigation and reward checking maps showed experience-dependent learning and were in register for distal visual cues. However, they showed a dissociation, whereby distal auditory cues failed to support spatial navigation but did support spatially localized reward checking. These findings indicate that rats can navigate in virtual space with only distal visual cues, without significant vestibular or other sensory inputs. Furthermore, they reveal the simultaneous dissociation between two reward-driven behaviors.