Climate change models predict increased drought frequency and severity, a threat to rain-fed crops like common bean (Phaseolus vulgaris L.). Drought adversely affects plant growth, reducing crop yield and quality by limiting carbon (C) and nitrogen (N) supply. While carbon partitioning and sink-source relationships under drought have been extensively studied, the role of nitrogen remobilisation in drought tolerance remains underexplored. This study compares C metabolism and N remobilisation in two common bean genotypes, S156 and R123, submitted to a terminal drought. In response to water limitation, S156 plants exhibited earlier leaf proteolysis notably via a stimulation of papain-like cysteine proteases activity and enhanced nitrogen remobilisation. Both processes were likely responsible for the absence of impact of the terminal drought on the N status of S156 seeds and were sustained by early N acquisition. In comparison, N acquisition and accumulation in R123 relied more on N uptake balanced between vegetative and reproductive stages. We speculated that late N acquisition in R123 was hindered by the terminal drought treatment, and that was not compensated for by drought-induced N remobilisation. These findings highlighted distinct carbon and nitrogen strategies and underscored the importance of N remobilisation for drought tolerance in common bean.

Summary Improving seed protein content without compromising carbon allocation or yield is a major challenge for enhancing nitrogen use efficiency. Here, we show that redirecting vacuolar nitrate transport through concurrent manipulation of tonoplast proteins controlling nitrate storage or export provides an effective lever to reprogram nitrogen allocation from leaves toward the seeds. Using Arabidopsis thaliana Ws lines disrupted for the vacuolar CLC-a nitrate importer and/or overexpressing the NRT2.7 tonoplast nitrate exporter, we show that plants combining the two modifications ( 35S::NRT2.7(clc-a)) integrate reduced nitrogen retention in vegetative tissues with increased nitrogen allocation to seeds. As a result, 35S::NRT2.7(clc-a) plants exhibit the strongest increase in seed protein content among all genotypes (approximately +25%) without affecting seed yield, carbon concentration, or lipid composition. Altered vacuolar nitrate fluxes in 35S::NRT2.7(clc-a) stimulate nitrate assimilation, enhance nitrate reductase activity and amino acid biosynthetic pathways, and drive coordinated reprogramming of nitrogen and carbon metabolisms. Through 15 N pulse–chase experiments, we confirmed that 35S::NRT2.7(clc-a) shows the highest nitrogen remobilization efficiency toward seeds. Overexpression of the barley NRT2.7 homolog HvNRT2.10 in Arabidopsis wild type and clc-a backgrounds reproduces the key features of 35S::NRT2.7 phenotype, demonstrating the conservation of NRT2.7 regulatory effects on plant metabolism across species. Together, these findings identify vacuolar nitrate transport as a promising target to modulate grain protein content in cereals through genetic strategies acting on nitrogen storage and remobilization. HIGHLIGHTS Vacuolar nitrate transport modifications ( clc-a, 35S::NRT2.7 , 35S::NRT2.7(clc-a) ) increase seed nitrogen and protein concentrations without altering seed yield or carbon levels, highlighting a selective enhancement in nitrogen storage. NRT2.7 overexpression (especially in the clc-a background) redirects nitrogen resources from vegetative tissues to the seeds, emphasizing the role of NRT2.7 in nitrogen remobilization. Proteomic analyses revealed distinct and contrasting profiles between clc-a and 35S::NRT2.7 , with 35S::NRT2.7(clc-a) , exhibiting unique effects in auxin transport and immunity pathways. Overexpression of barley homolog of AtNRT2.7, HvNRT2.10 , in Arabidopsis confirmed conserved role for NRT2.7 family in boosting seed nitrogen concentration and NUE in wild type and in a larger extent in the clc-a background.

Root senescence remains largely unexplored. In this study, the time-course of the morphological, metabolic, and proteomic changes occurring with root aging were investigated, providing a comprehensive picture of the root senescence program. We found novel senescence-related markers for the characterization of the developmental stage of root tissues. The rapeseed root system is unique in that it consists of the taproot and lateral roots. Our study confirmed that the taproot, which transiently accumulates large quantities of starch and proteins, is specifically dedicated to nutrient storage and remobilization, while the lateral roots are mainly dedicated to nutrient uptake. Proteomic data from the taproot and lateral roots highlighted the different senescence-related events that control nutrient remobilization and nutrient uptake capacities. Both the proteome and enzyme activities revealed senescence-induced proteases and nucleotide catabolic enzymes that deserve attention as they may play important roles in nutrient remobilization efficiency in rapeseed roots. Taking advantage of publicly available transcriptomic and proteomic data on senescent Arabidopsis leaves, we provide a novel lists of senescence-related proteins specific or common to root organs and/ or leaves.

An efficient nitrate uptake system contributes to the improvement of crop nitrogen use efficiency under low nitrogen availability. The High Affinity nitrate Transport System (HATS) in plants is active in low range of external nitrate and is mediated by a two-component system (high affinity transporters NRT2 associated to a partner protein NRT3 (NAR2)). In Brachypodium, the model plant for C3 cereals, we investigated the role of BdNRT2A and BdNRT3.2 through various experimental approaches. Expression profile of BdNRT2.A and BdNRT3.2 genes in response to nitrate availability fits perfectly with the characteristics of the HATS components. 15Nitrate influx measurements decreased in bdnrt2a mutants (one NaN3 induced mutant with a truncated NRT2A protein and two amiRNA mutants). In addition, the N limited phenotype of the mutant with a truncated NRT2A protein confirmed that BdNRT2A is a major contributor of the HATS in Brachypodium. An effective nitrate transport in the heterologous expression system Xenopus oocytes required the coexpression of BdNRT2A and BdNRT3.2 that characterizes two-component system of the HATS. Functional interaction between BdNRT2A-GFP and BdNRT3.2-RFP fusion proteins was observed at the plasma membrane in Arabidopsis protoplasts in transient expression experiments with BdNRT3.2 being necessary for the plasma membrane localization of BdNRT2A. The role of a conserved Ser residue in BdNRT2A (S461) specific to monocotyledons was evaluated in the BdNRT2A and BdNRT3.2 interaction leading to plasma membrane targeting. Assuming that S461 could be regulated by phosphorylation, a directed mutagenesis was performed to mimic a nonphosphorylated (S461A) or a constitutively phosphorylated (S461D), However, the mimicking the phosphorylation status of S461 by mutagenesis did not modify the BdNRT2A and BdNRT3.2 interaction, suggesting a more complex regulating mechanism. In conclusion, our data show that BdNRT2A and BdNRT3.2 are the main components of the nitrate HATS activity in Brachypodium (Bd21-3) and allow an optimal growth in low N conditions.

During leaf senescence, autophagy plays a critical role by removing damaged cellular components and participating in nutrient remobilization to sink organs. However, how AUTOPHAGY (ATG) genes are regulated during natural leaf senescence remains largely unknown. In this study, we attempted to identify upstream transcriptional regulator(s) of ATG genes and their molecular basis during leaf senescence in Arabidopsis through the combined analyses of promoter binding, autophagy flux, and genetic interactions. We found that PHYTOCHROME-INTERACTING FACTOR4 (PIF4) and PIF5 directly bind to the promoters of ATG5, ATG12a, ATG12b, ATG8a, ATG8e, ATG8f, and ATG8g, inducing their transcription. These target ATG genes are down-regulated in pif4, pif5, and pif4pif5 mutants, resulting in decreased autophagic activity and slower degradation of chloroplast proteins and chlorophyll. Conversely, overexpression of ATG8 genes accelerated protein degradation with early leaf senescence. Moreover, our data suggested partial suppression of the pif4pif5 phenotype by ATG8a overexpression. PIF4/PIF5 also influence senescence induced by nutrient starvation, another hallmark of the autophagy pathway. Furthermore, we observed that the PIF4/PIF5-ATG regulatory module may contribute to seed maturation. Our study not only unveils transcriptional regulators of autophagy in natural leaf senescence but also underscores the potential role of PIF4/PIF5 as functional regulators in leaf senescence and nutrient remobilization.

Societal Impact Statement Cereal‐legume intercropping is a promising strategy for sustainable agroecosystems, leveraging the biological complementarities between plant species to reduce the need for inputs while enhancing field biodiversity. Here, we focused on maize‐bean intercropping, which is experiencing a revival in conventional agricultural settings. In such settings, intercropping was characterized more by competition than synergy, primarily affecting yield and gene expression in beans, which, despite a reduced yield, produced larger seeds. Our findings highlight the importance of selecting suitable varieties and adjusting agricultural practices to take full advantage of the intercrop. Summary Cereal‐legume intercropping is a promising strategy for sustainable agroecosystems. The traditional intercropping of maize and bean is experiencing a revival in some modern agricultural settings, such as in southwestern France, where maize hybrids are intercropped with the commercialized Tarbais bean. We conducted on‐farm surveys and a field assay to address the following questions: How does the cropping system impact yield, nutrient uptake, and rhizosphere bacterial assemblages? Do positive or negative interactions between maize and beans dominate in intercropping? What is the effect of intercropping on plant transcriptomics? We recorded farming practices, conducted yield and nutrient measurements, and characterized soil bacterial assemblages to compare sole‐cropped maize and beans with intercropped plants. A controlled field assay was also established to extend this comparison to plant gene expression differences. Intercropping was associated with a trend toward increased bacterial diversity. The cropping system significantly influenced agronomic traits, with frequent farm‐by‐cropping system interactions underscoring the critical role of farming practices. Competition dominated maize‐bean intercropping, with 34 negative correlations among the 47 significant ones between maize and bean traits. This competition affected yield and nutrition, but primarily impacted beans, which produced fewer but bigger/heavier seeds. Transcriptomic results concurred with these findings, revealing no differentially expressed genes in maize but 5,070 in beans under competition. Overall, our findings suggest that beneficial interactions between the two crops are hindered under current field conditions, underscoring the importance of carefully considering partner varieties and farming practices to revive traditional agricultural systems.

Autophagy is essential for homeostasis and nutrient recycling. Its activity increases with aging and in response to deficiencies. The effects of defective autophagy on root metabolism have not yet been described. Addressing this question through root proteome analyses, we found that most V-ATPases were less abundant in the roots of autophagy mutants than in wild type. V-ATPases deficit, associated with lower root water contents and lower nitrate, magnesium, and potassium concentrations, indicated that the disturbance of cellular ion and water management in autophagy mutants was likely related to vacuole function. Isotopic δ13C analyses and leaf temperature measurements using thermography showed that water deficit in autophagy mutants was not due to excess transpiration, as the conductance of stomata was reduced in mutants compared to wild type. Many proteins related to the catabolism of amino acids and lipids and the tricarboxylic acid (TCA) cycle were over-abundant in atg mutants. The increase in several proteases that paralleled amino acid catabolism suggested that in the absence of autophagic flux, compensatory processes could be established to degrade proteins, recycle amino acids, and fuel TCA. Whether the V-ATPases defect affects energy metabolism and promotes lipid and amino acid catabolism to compensate and fuel TCA remains to be explored. In conclusion, this report establishes for the first time a correlation between autophagy and vacuole function through V-ATPases, particularly with regard to water and ion management. Additionally, this report shows the exacerbation of amino acid catabolism in relation to the stimulation of the TCA cycle in autophagy mutants.

A 2-years assessment of nitrogen (N) stocks, tree N safety nets (from a 15N labeling experiment), and biological N fixation was conducted in a Mediterranean agroforestry system in southern France. The study aimed to quantify N retention in agroforestry. The study area is characterized by a skeletic rhodic luvisol soil, a mean annual temperature of 15.5 degrees C, and an average annual precipitation of 556 mm. N and 15N were quantified across all system components, which are N-fixing black locust trees, crops, weed plants, understory vegetation strips (UVS), rhizospheric soil, and soil microbial biomass. A split-plot experimental design was used, with agroforestry (AF) and monoculture (MC) plots. 15N labeling was applied to track N fluxes and determine tree nutrient absorption over time. We hypothesized that tree root growth and nutrient leaching would enhance the safety-net effect, improving N retention. Results showed that crops in AF had lower N stocks (13-30% less than MC), but tree and UVS contributions compensated for the deficit, leading to a 62% increase in total plot-level N stock in 2022. The Relative Nitrogen Content was 0.97 in 2021 and 1.63 in 2022. While no 15N was detected in trees in the first year (70 days after labeling), 2% of applied 15N was recovered in trees 14 months post-labeling. % of N derived from atmospheric N2 (%Ndfa) ranged from 52 to 68%, with trees fixing 14-18 kg N ha-1. We confirmed that agroforestry enhances N retention, but further research is needed to quantify leaching and gaseous losses of nitrogen.

In plants, a large part of the nutrients used to generate seed lipid and protein reserves is derived from both the degradation of macromolecules in source leaves and the transfer of small catabolic molecules like amino acids from the senescing leaves to the seeds. Studies of autophagy mutants in Arabidopsis showed that autophagy is a master player controlling 60% of the remobilization of nitrogen from senescing leaf tissues to developing seeds, and strongly impacting reserve deposition, especially in the protein to lipid ratio. Since autophagy is largely enhanced in leaves during senescence and in the seeds during maturation, we investigated the roles of autophagy in these sources and sink tissues, to identify checkpoints controlling seed filling and quality. Through gene complementation using tissue-specific promoters, we demonstrated that while autophagy regulates nitrogen flux to the seeds in source leaves, the autophagy taking place in seeds during their maturation is essential to reach the appropriate seed quality in terms of C and N storage. Overall, these results highlight the multiple roles of autophagy in the optimal development of the plant throughout its entire lifespan

This preliminary study shows that Brassica napus WSCP1 delays chlorophyll degradation and inhibits serine proteases during dark-induced leaf senescence in Arabidopsis. In Brassica napus L., one of the levers for improving Nitrogen Remobilization Efficiency (NRE) consists to delay senescence onset, which prolongs leaf lifespan and reduces the asynchronism between the nitrogen emptying period in these source organs and the filling period of seeds. Water soluble chlorophyll binding proteins (WSCPs) may have a dual function in chlorophyll protection and protease inhibition. As such they are excellent candidates to propose a technical solution to delay leaf senescence. Several isoforms of WSCPs have been identified in the leaves of rapeseed. Among them, WSCP1 presents two motifs in its protein sequence that are associated to the putative dual function. To test if WSCP1 can actually delay leaf senescence, the overexpression of WSCP1 under the control of the SAG12 senescence promoter (pSAG12::WSCP1) was developed in an Arabidopsis thaliana accession that was previously described as early senescent (RIL232). During dark-induced senescence, our main results reveal a lower chlorophyll degradation and a reduction of the serine proteases (SPs) activity in leaves of pSAG12::WSCP1 lines compared to RIL232. Although SP inhibition was strong in pSAG12::WSCP1 leaves compared with RIL232, no difference in leaf protein content was observed. This result suggests either the recruitment of a compensatory proteolytic system in WSCP1-overexpressing lines or that SPs are not essential for protein nitrogen remobilization during dark-induced leaf senescence.

Biostimulant use is a promising agricultural strategy to maintain yield while decreasing mineral fertilisers and pesticides. Whereas the positive effect of protein hydrolysates (PH) on growth and yield has already been described, the underlying processes are not well understood. To better identify and characterise the physiological and molecular targets of PH, we first carried out in vitro experiments using the model species Arabidopsis thaliana. PH stimulated Arabidopsis root growth in a dose-dependent manner, with high concentrations inhibiting growth. After having determined a stimulating PH concentration, we performed metabolomic and transcriptomic analyses. We observed that PH application increased amino acid levels in the plants, including a high level of glutamine, although it was only present in trace amounts in PH. These results suggest that amino acids are taken up and metabolized in the plant. PH also had a profound impact on the Arabidopsis transcriptome, with genes involved in nitrate and amino acid transport and assimilation showing a clear up- and down-regulation, respectively. For example, the expression of the high-affinity nitrate transporter NRT2.1 (NITRATE TRANSPORTER 2) was decreased, and consistently high-affinity nitrate uptake and the development of lateral roots were diminished. The PH contained high levels of branched amino acids, which are known to induce the TOR kinase activity, a major driver of growth. Finally, high-throughput phenotyping also showed that PH supply increased shoot growth. In conclusion, our findings show that PH has a clear and robust effect on Arabidopsis growth, but also on the transcriptome, metabolite levels, and physiological processes like nitrogen metabolism.

BACKGROUND AND AIMS:Macroautophagy is essential for the degradation and recycling of various macromolecules in eukaryote cells. In plants, autophagy is involved in the degradation of damaged chloroplasts in response to stress. Autophagy is a key player in nitrogen management at the whole-plant level, and autophagy mutants display strong defects in nitrogen remobilization and early leaf senescence phenotypes especially under nitrogen source limitation. It is known that leaf senescence is associated to nutrient remobilization processes and is induced by nitrate limitation. However, it remains to be determined which actors are involved in this interplay and whether nutrient remobilization acts as a signal that enhances leaf senescence or whether senescence-associated chloroplast degradation promotes nutrient remobilization. In this context, our aim is to demine whether the level of autophagy activity controls leaf longevity and influences the progress of leaf senescence balancing resources and waste management. METHODS:In this study, we used Arabidopsis autophagy knock-out mutants (atg) and plants overexpressing autophagy associated genes (ATG8-OE) to compare their phenotypes to wild type under both sufficient nitrate condition and nitrate starvation. KEY RESULTS:The transfer from nitrate-sufficient conditions to nitrate starvation accelerated leaf senescence in all the genotypes. Unexpectedly, under both sufficient and nitrate-starved conditions, both atg mutants and ATG8 over-expressors exhibited earlier leaf senescence phenotypes compared to wild type. Given that autophagy is a longevity factor, the more severe leaf senescence phenotype of over-expressors was puzzling. This study highlights a relationship between autophagy, nitrogen remobilization and leaf senescence and shows how the fine tuning of nutrient management can influence senescence onset. CONCLUSIONS:The fine-tuning of autophagy is necessary to control leaf senescence.

Plant responses to nutrient availability are critical for plant development and yield. Nitrate, the major form of nitrogen in most soils, serves as both a nutrient and signaling molecule. Nitrate itself triggers rapid, major changes in gene expression, especially via nodule inception (NIN)-like protein (NLP) transcription factors, and stimulates protein phosphorylation. Mitogen-activated protein kinase (MAPK)-related genes are among the early nitrate-responsive genes; however, little is known about their roles in nitrate signaling pathways. Here, we show that nitrate resupply to nitrogen-depleted Arabidopsis (Arabidopsis thaliana) plants triggers, within minutes, an MAPK cascade that requires NLP-dependent transcriptional induction of mitogen-activated protein kinase kinase kinase 13 (MAP3K13) and MAP3K14 and that the MAPK cascade is composed of MKK3 and likely C-clade MAPKs (MPK1/2/7/14). Importantly, nitrate reductase-deficient mutants exhibited nitrate-induced MPK7 activities comparable to those observed in wild-type plants, indicating that nitrate itself is the signal that stimulates the cascade. We show that the modified expression of MAP3K13 and MAP3K14 affects nitrate-stimulated BT2 expression and modulates plant responses to nitrogen availability, such as nitrate uptake and senescence. Our finding that an MAPK cascade involving MAP3K13 and MAP3K14 functions in the complex regulatory network governing responses to nitrate availability will guide future strategies to optimize plant responses to nitrogen fertilization and nitrogen use efficiency.

Cereal-legume intercropping is emerging as a promising strategy for fostering more sustainable agroecosystems. The traditional farming system of maize-bean intercropping, originating from Central America, where both crops were domesticated, is experiencing a revival in modern agricultural settings. This is exemplified in southwestern France, where maize hybrids are intercropped with the recently commercialized Tarbais bean variety. Here, we combined on-farm investigations of agronomic practices, plant yield and nutrition measurements, characterization of soil and bacterial assemblages by metabarcoding, along with transcriptomic assays to compare the performance of sole cropped maize and beans to intercropped plants. Agronomic practices and soil-related variables differed among farms, with results suggesting that farmers adjust the former according to soil mineralization level. Despite this farm-specific effect, we detected a notable increase in bacterial diversity in intercropping, both in bulk and rhizosphere soil. Multivariate analyses unveiled a significant impact of cropping systems on agronomic traits in maize and beans, with frequent farm-by-cropping system interactions (11 of 22 traits in maize and 12 of 24 traits in bean). Competition dominated maize-bean intercropping, with 54 of 89 significant correlations between maize and bean traits being negative. Beans were notably impacted by this competition, yielding fewer seeds in intercropped conditions, albeit exhibiting higher seed size and weight, as well as nitrogen and carbon percentages. We set up a controlled field assay to quantify differentially expressed (DE) genes between cropping conditions for the two species. While competition between the two crops was much more severe than on-farm, we found that it primarily affected the bean and its transcriptome, with nearly 30% of DE genes vs none in maize. Overall, our findings suggest that synergies between the two crops are likely hindered, underscoring the importance of carefully considering partner varieties and agronomic practices in the revival of traditional agricultural systems.### Competing Interest StatementThe authors have declared no competing interest.

This study aimed to assess crop yield and soil nitrogen removal by trees from a potential nitrogen leaching pool in Mediterranean agroforestry, in a 15N-labeled fertilizer field experiment. We hypothesized that the applied 15N would be taken up by the trees, understorey vegetation strip (UVS), and soil microbial biomass, and that crop yield would be reduced in agroforestry systems. In a two-block agroforestry design, 15N-labeled urea was applied to the crop-soil surface in agroforestry and monocrop plots. We analyzed the 15N, nitrogen, and carbon contents of the aboveground and belowground compartments of the trees, crops, and UVS, as well as that of the soil microbial biomass. No labelled 15N was found in the trees, UVS and microbial biomass. Additionally, agroforestry-crop yielded a -20

Autophagy is a vesicular mechanism that plays a fundamental role in nitrogen remobilization from senescing leaves to seeds. The Arabidopsis (Arabidopsis thaliana) autophagy (atg) mutants exhibit early senescence, reduced biomass, and low seed yield. The atg seeds also exhibit major changes in N and C concentrations. During plant development, autophagy genes are expressed in the source leaves and in the sink seeds during maturation. We thus addressed the question of whether the seed composition defects in atg mutants are caused by defective N remobilization from source leaves or whether they are due to the absence of autophagy in seeds during maturation. To answer this question, we restored autophagy activity in the atg5 mutant by expressing the wild-type (WT) ATG5 allele specifically in source leaves using the senescence-associated gene 12 (SAG12) promoter or specifically in seeds using the Glycinin-1 promoter, or in both organs using both constructs. In atg5, N remobilization from the rosettes to seeds was almost completely reestablished when transformed with the pSAG12::ATG5 construct. However, transformation with the pSAG12::ATG5 construct only partially restored seed composition. In contrast, seed N and C composition was largely restored by transformation with the pGly::ATG5 construct, even though the early leaf senescence phenotype was maintained in the atg5 background. Cotransformation with pSAG12::ATG5 and pGly::ATG5 completely restored the WT remobilization and seed composition phenotypes. Our results highlight the essential role of autophagy in leaves for nitrogen supply and in seeds for the establishment of carbon and nitrogen reserves.

Understanding plant responses to individual stresses does not mean that we understand real-world situations, where stresses usually combine and interact. These interactions arise at different levels, from stress exposure to the molecular networks of the stress response. Here, we built an in-depth multiomic description of plant responses to mild water (W) and nitrogen (N) limitations, either individually or combined, among 5 genetically different Arabidopsis (Arabidopsis thaliana) accessions. We highlight the different dynamics in stress response through integrative traits such as rosette growth and the physiological status of the plants. We also used transcriptomic and metabolomic profiling during a stage when the plant response was stabilized to determine the wide diversity in stress-induced changes among accessions, highlighting the limited reality of a "universal" stress response. The main effect of the W x N interaction was an attenuation of the N-deficiency syndrome when combined with mild drought, but to a variable extent depending on the accession. Other traits subject to W x N interactions are often accession specific. Multiomic analyses identified a subset of transcript-metabolite clusters that are critical to stress responses but essentially variable according to the genotype factor. Including intraspecific diversity in our descriptions of plant stress response places our findings in perspective. A multiomic analysis describes the response to mild water and nitrogen limitations, individually or combined, in 5 Arabidopsis thaliana accessions from different origins.

Maize is currently the most productive cereal crop in the world ([www.faostat.org][1]). Maize can form a symbiotic relationship with the Arbuscular Mycorrhizal Fungus MF, Rhizophagus irregularis . In this relationship, the fungus provides the plant with additional water and mineral nutrients, while the plant supplies carbon compounds to the fungus. Two maize lines were studied, and they exhibited contrasting responses to AMF inoculation based on their physiological and molecular characteristics. Interestingly, the beneficial effects of the AMF were observed mainly under conditions of limited N fertilization. Under such conditions, the AMF helped maintain plant biomass production even when there was a significant reduction in N supply. The availability of nitrogen was found to be a crucial factor influencing all the traits studied. This suggests that the level of N supply plays a pivotal role in determining how the maize plants interact with the AMF. Despite the two maize lines showing different transcriptomic and metabolomic responses to R. irregularis , their agro-physiological traits remained similar. This indicates that while there may be genetic differences in how the plants respond at the molecular level, the overall growth and productivity outcomes are comparable. Both the plant and fungal transcriptomes were more significantly influenced by the level of N nutrition rather than the specific maize genotype. This suggests that N availability has a more profound impact on gene expression in both organisms than the genetic makeup of the maize plant. To understand the metabolic implications of this symbiotic relationship, we integrated transcriptomic data into a multi-organ Genome-scale metabolic model (GSM) called iZMA6517 based on a stoichiometric approach. This modelling approach highlighted nucleotide and ureides metabolism as previously unrecognized factors contributing to the symbiotic N nutrition facilitated by R. irregularis , thereby enhancing maize growth.### Competing Interest StatementThe authors have declared no competing interest. [1]: http://www.faostat.org

ABSTRACTSenescence related markers have been widely studied in leaves in many plant species. Root senescence is more difficult to characterize. The existence of two different root organs inB. napus,with a taproot that appear to be specifically dedicated to the storage and remobilization of nutrients, offered the possibility of analysing the temporality of the changes linked to aging, based on the degradation of the taproot reserves. Microscopic and biochemical analyses showed that taproot plays an important role in carbon and nitrogen storage as reflected by the large quantities of starch and proteins present at early development stages. The proteomic study associated to the description of biochemical, morphological and anatomic changes provides a comprehensive picture of the main events occurring in the taproot and in the lateral roots with aging. Master modifications as protein and cell wall degradation, amino acid catabolism versus synthesis, nucleic acid degradation are presented and senescence related markers specific or not of the root types were identified. Comparison with Arabidopsis public data facilitated the identification of markers common to root and leaf senescence. The analysis of protease changes provides a list of candidates that may play a role in nitrogen and carbohydrate remobilization from taproot to the shoot and flowering organs and that would deserve attention for further functional analyses.

P4B (2-phenyl-1-[4-(6-(piperidin-1-yl) pyridazin-3-yl) piperazin-1-yl] butan-1-one) is a novel cellulose biosynthesis inhibitor (CBI) discovered in a screen for molecules to identify inhibitors of Arabidopsis (Arabidopsis thaliana) seedling growth. Growth and cellulose synthesis inhibition by P4B were greatly reduced in a novel mutant for the cellulose synthase catalytic subunit gene CESA3 (cesa3pbr1). Cross-tolerance to P4B was also observed for isoxaben-resistant (ixr) cesa3 mutants ixr1-1 and ixr1-2. P4B has an original mode of action as compared with most other CBIs. Indeed, short-term treatments with P4B did not affect the velocity of cellulose synthase complexes (CSCs) but led to a decrease in CSC density in the plasma membrane without affecting their accumulation in microtubule-associated compartments. This was observed in the wild type but not in a cesa3pbr1 background. This reduced density correlated with a reduced delivery rate of CSCs to the plasma membrane but also with changes in cortical microtubule dynamics and orientation. At longer timescales, however, the responses to P4B treatments resembled those to other CBIs, including the inhibition of CSC motility, reduced growth anisotropy, interference with the assembly of an extensible wall, pectin demethylesterification, and ectopic lignin and callose accumulation. Together, the data suggest that P4B either directly targets CESA3 or affects another cellular function related to CSC plasma membrane delivery and/or microtubule dynamics that is bypassed specifically by mutations in CESA3.