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Despite its worldwide economic importance for food (oil, meal) and non-food (green energy and chemistry) uses, oilseed rape has a low nitrogen (N) use efficiency (NUE), mainly due to the low N remobilization efficiency (NRE) observed during the vegetative phase when sequential leaf senescence occurs. Assuming that improvement of NRE is the main lever for NUE optimization, unravelling the cellular mechanisms responsible for the recycling of proteins (the main N source in leaf) during sequential senescence is a prerequisite for identifying the physiological and molecular determinants that are associated with high NRE. The development of a relevant molecular indicator (SAG12/Cab) of leaf senescence progression in combination with a N-15-labelling method were used to decipher the N remobilization associated with sequential senescence and to determine modulation of this process by abiotic factors especially N deficiency. Interestingly, in young leaves, N starvation delayed senescence and induced BnD22, a water-soluble chlorophyll-binding protein that acts against oxidative alterations of chlorophylls and exhibits a protease inhibitor activity. Through its dual function, BnD22 may help to sustain sink growth of stressed plants and contribute to a better utilization of N recycled from senescent leaves, a physiological trait that could improve NUE. Proteomics approaches have revealed that proteolysis involves chloroplastic FtsH protease in the early stages of senescence, aspartic protease during the course of leaf senescence, and the proteasome beta 1 subunit, mitochondria processing protease and SAG12 (cysteine protease) during the later senescence phases. Overall, the results constitute interesting pathways for screening genotypes with high NRE and NUE.

Backgrounds and Aims Extreme climatic events such as severe droughts are expected to increase with climate change and to limit grassland perennity. The present study aimed to characterize the adaptive responses by which temperate herbaceous grassland species resist, survive and recover from a severe drought and to explore the relationships between plant resource use and drought resistance strategies. Methods Monocultures of six native perennial species from upland grasslands and one Mediterranean drought-resistant cultivar were compared under semi-controlled and non-limiting rooting depth conditions. Above- and below-ground traits were measured under irrigation in spring and during drought in summer (50 d of withholding water) in order to characterize resource use and drought resistance strategies. Plants were then rehydrated and assessed for survival (after 15 d) and recovery (after 1 year). Key Results Dehydration avoidance through water uptake was associated with species that had deep roots (>1·2 m) and high root mass (>4 kg m−3). Cell membrane stability ensuring dehydration tolerance of roots and meristems was positively correlated with fructan content and negatively correlated with sucrose content. Species that survived and recovered best combined high resource acquisition in spring (leaf elongation rate >9 mm d−1 and rooting depth >1·2 m) with both high dehydration avoidance and tolerance strategies. Conclusions Most of the native forage species, dominant in upland grassland, were able to survive and recover from extreme drought, but with various time lags. Overall the results suggest that the wide range of interspecific functional strategies for coping with drought may enhance the resilience of upland grassland plant communities under extreme drought events.

Livestock is a major driver in most rural landscapes and economics, but it also polarises debate over its environmental impacts, animal welfare and human health. Conversely, the various services that livestock farming systems provide to society are often overlooked and have rarely been quantified. The aim of analysing bundles of services is to chart the coexistence and interactions between the various services and impacts provided by livestock farming, and to identify sets of ecosystem services (ES) that appear together repeatedly across sites and through time. We review three types of approaches that analyse associations among impacts and services from local to global scales: (i) detecting ES associations at system or landscape scale, (ii) identifying and mapping bundles of ES and impacts and (iii) exploring potential drivers using prospective scenarios. At a local scale, farming practices interact with landscape heterogeneity in a multi-scale process to shape grassland biodiversity and ES. Production and various ES provided by grasslands to farmers, such as soil fertility, biological regulations and erosion control, benefit to some extent from the functional diversity of grassland species, and length of pasture phase in the crop rotation. Mapping ES from the landscape up to the EU-wide scale reveals a frequent trade-off between livestock production on one side and regulating and cultural services on the other. Maps allow the identification of target areas with higher ecological value or greater sensitivity to risks. Using two key factors (livestock density and the proportion of permanent grassland within utilised agricultural area), we identified six types of European livestock production areas characterised by contrasted bundles of services and impacts. Livestock management also appeared to be a key driver of bundles of services in prospective scenarios. These scenarios simulate a breakaway from current production, legislation (e.g. the use of food waste to fatten pigs) and consumption trends (e.g. halving animal protein consumption across Europe). Overall, strategies that combine a reduction of inputs, of the use of crops from arable land to feed livestock, of food waste and of meat consumption deliver a more sustainable food future. Livestock as part of this sustainable future requires further enhancement, quantification and communication of the services provided by livestock farming to society, which calls for the following: (i) a better targeting of public support, (ii) more precise quantification of bundles of services and (iii) better information to consumers and assessment of their willingness to pay for these services.

It has long been recognized that plant species and soil microorganisms are tightly linked, but understanding how different species vary in their effects on soil is currently limited. In this study, we identified those plant characteristics (identity, specific functional traits, or resource acquisition strategy) that were the best predictors of nitrification and denitrification processes. Ten plant populations representing eight species collected from three European grassland sites were chosen for their contrasting plant trait values and resource acquisition strategies. For each individual plant, leaf and root traits and the associated potential microbial activities (i.e., potential denitrification rate [DEA], maximal nitrification rate [NEA], and NH 4 + affinity of the microbial community [NHS com ]) were measured at two fertilization levels under controlled growth conditions. Plant traits were powerful predictors of plant-microbe interactions, but relevant plant traits differed in relation to the microbial function studied. Whereas denitrification was linked to the relative growth rate of plants, nitrification was strongly correlated to root trait characteristics (specific root length, root nitrogen concentration, and plant affinity for NH 4 + ) linked to plant N cycling. The leaf economics spectrum (LES) that commonly serves as an indicator of resource acquisition strategies was not correlated to microbial activity. These results suggest that the LES alone is not a good predictor of microbial activity, whereas root traits appeared critical in understanding plant-microbe interactions.

Autophagy is essential for protein degradation, nutrient recycling, and nitrogen remobilization. Autophagy is induced during leaf ageing and in response to nitrogen starvation, and is known to play a fundamental role in nutrient recycling for remobilization and seed filling. Accordingly, ageing leaves of Arabidopsis autophagy mutants (atg) have been shown to over-accumulate proteins and peptides, possibly because of a reduced protein degradation capacity. Surprisingly, atg leaves also displayed higher protease activities. The work reported here aimed at identifying the nature of the proteases and protease activities that accumulated differentially (higher or lower) in the atg mutants. Protease identification was performed using shotgun LC-MS/MS proteome analyses and activity-based protein profiling (ABPP). The results showed that the chloroplast FTSH (FILAMENTATION TEMPERATURE SENSITIVE H) and DEG (DEGRADATION OF PERIPLASMIC PROTEINS) proteases and several extracellular serine proteases [subtilases (SBTs) and serine carboxypeptidase-like (SCPL) proteases] were less abundant in atg5 mutants. By contrast, proteasome-related proteins and cytosolic or vacuole cysteine proteases were more abundant in atg5 mutants. Rubisco degradation assays and ABPP showed that the activities of proteasome and papain-like cysteine protease were increased in atg5 mutants. Whether these proteases play a back-up role in nutrient recycling and remobilization in atg mutants or act to promote cell death is discussed in relation to their accumulation patterns in the atg5 mutant compared with the salicylic acid-depleted atg5/sid2 double-mutant, and in low nitrate compared with high nitrate conditions. Several of the proteins identified are indeed known as senescence- and stress-related proteases or as spontaneous cell-death triggering factors.

Processes allowing the recycling of organic nitrogen and export to young leaves and seeds are important determinants of plant yield, especially when plants are nitrate-limited. Because autophagy is induced during leaf ageing and in response to nitrogen starvation, its role in nitrogen remobilization was suspected. It was recently shown that autophagy participates in the trafficking of Rubisco-containing bodies to the vacuole. To investigate the role of autophagy in nitrogen remobilization, several autophagy-defective (atg) Arabidopsis mutants were grown under low and high nitrate supplies and labeled with at the vegetative stage in order to determine 15N partitioning in seeds at harvest. Because atg mutants displayed earlier and more rapid leaf senescence than wild type, we investigated whether their defects in nitrogen remobilization were related to premature leaf cell death by studying the stay-green atg5.sid2 and atg5.NahG mutants. Results showed that nitrogen remobilization efficiency was significantly lower in all the atg mutants irrespective of biomass defects, harvest index reduction, leaf senescence phenotypes and nitrogen conditions. We conclude that autophagy core machinery is needed for nitrogen remobilization and seed filling.

Phloem-derived amino acids are the major source of nitrogen supplied to developing seeds. Amino acid transfer from the maternal to the filial tissue requires at least one cellular export step from the maternal tissue prior to the import into the symplasmically isolated embryo. Some members of UMAMIT (usually multiple acids move in an out transporter) family (UMAMIT11, 14, 18, 28, and 29) have previously been implicated in this process. Here we show that additional members of the UMAMIT family, UMAMIT24 and UMAMIT25, also function in amino acid transfer in developing seeds. Using a recently published yeast-based assay allowing detection of amino acid secretion, we showed that UMAMIT24 and UMAMIT25 promote export of a broad range of amino acids in yeast. In plants, UMAMIT24 and UMAMIT25 are expressed in distinct tissues within developing seeds; UMAMIT24 is mainly expressed in the chalazal seed coat and localized on the tonoplast, whereas the plasma membrane-localized UMAMIT25 is expressed in endosperm cells. Seed amino acid contents of umamit24 and umamit25 knockout lines were both decreased during embryogenesis compared with the wild type, but recovered in the mature seeds without any deleterious effect on yield. The results suggest that UMAMIT24 and 25 play different roles in amino acid translocation from the maternal to filial tissue; UMAMIT24 could have a role in temporary storage of amino acids in the chalaza, while UMAMIT25 would mediate amino acid export from the endosperm, the last step before amino acids are taken up by the developing embryo.

Glutamine synthetase (GS) is central for ammonium assimilation and consists of cytosolic (GS1) and chloroplastic (GS2) isoenzymes. During plant ageing, GS2 protein decreases due to chloroplast degradation, and GS1 activity increases to support glutamine biosynthesis and N remobilization from senescing leaves. The role of the different Arabidopsis GS1 isoforms in nitrogen remobilization was examined using 15N tracing experiments. Only the gln1;1-gln1; 2-gln1; 3 triple-mutation affecting the three GLN1;1, GLN1;2, and GLN1; 3 genes significantly reduced N remobilization, total seed yield, individual seed weight, harvest index, and vegetative biomass. The triple-mutant accumulated a large amount of ammonium that could not be assimilated by GS1. Alternative ammonium assimilation through asparagine biosynthesis was increased and was related to higher ASN2 asparagine synthetase transcript levels. The GS2 transcript, protein, and activity levels were also increased to compensate for the lack of GS1-related glutamine biosynthesis. Localization of the different GLN1 genes showed that they were all expressed in the phloem companion cells but in veins of different order. Our results demonstrate that glutamine biosynthesis for N-remobilization occurs in veins of all orders (major and minor) in leaves, it is mainly catalysed by the three major GS1 isoforms (GLN1; 1, GLN1; 2, and GLN1; 3), and it is alternatively supported by AS2 in the veins and GS2 in the mesophyll cells.

Despite its high capacity to take up nitrate from soil, winter rapeseed (Brassica napus) is characterized by a low N recovery in seeds. Thus, to maintain yield, rapeseed requires a high fertilization rate. Increasing nutrient use efficiency in rapeseed by addition of a biostimulant could help improve its agroenvironmental balance. The effects of marine brown seaweed Ascophyllum nodosum on plant growth have been well described physiologically. However, to our knowledge, no study has focused on transcriptomic analyses to determine metabolic targets of these extracts. A preliminary screening of different extracts revealed a significant effect of one of them (AZAL5) on rapeseed root (+102 %) and shoot ( 23 %) growth. Microarray analysis was then used on AZAL5-treated or nontreated plants to characterize changes in gene expression that were further supported by physiological evidence. Stimulation of nitrogen uptake (+21 and +115 % in shoots and roots, respectively) and assimilation was increased in a similar manner to growth, whereas sulfate content (+63 and +133 % in shoots and roots, respectively) was more strongly stimulated leading to sulfate accumulation. Among the identified genes whose expression was affected by AZAL5, MinE, a plastid division regulator, was the most strongly affected. Its effect was supported by microscopic analysis showing an enhancement of chloroplast number per cell and starch content but without a significant difference in net photosynthetic rate. In conclusion, it is suggested that AZAL5, which promotes plant growth and nutrient uptake, could be used as a supplementary tool to improve rapeseed agroenvironmental balance.

Epigenetics has emerged as an important research field for crop improvement under the on-going climatic changes. Heritable epigenetic changes can arise independently of DNA sequence alterations and have been associated with altered gene expression and transmitted phenotypic variation. By modulating plant development and physiological responses to environmental conditions, epigenetic diversity—naturally, genetically, chemically, or environmentally induced—can help optimise crop traits in an era challenged by global climate change. Beyond DNA sequence variation, the epigenetic modifications may contribute to breeding by providing useful markers and allowing the use of epigenome diversity to predict plant performance and increase final crop production. Given the difficulties in transferring the knowledge of the epigenetic mechanisms from model plants to crops, various strategies have emerged. Among those strategies are modelling frameworks dedicated to predicting epigenetically controlled-adaptive traits, the use of epigenetics for in vitro regeneration to accelerate crop breeding, and changes of specific epigenetic marks that modulate gene expression of traits of interest. The key challenge that agriculture faces in the 21st century is to increase crop production by speeding up the breeding of resilient crop species. Therefore, epigenetics provides fundamental molecular information with potential direct applications in crop enhancement, tolerance, and adaptation within the context of climate change.