Transcriptomic, Metabolomic and Ionomic Analyses Reveal Early Modulation of Leaf Mineral Content in Brassica napus under Mild or Severe Drought

Low Nitrogen Input Mitigates Quantitative but Not Qualitative Reconfiguration of Leaf Primary Metabolism in Brassica napus L. Subjected to Drought and Rehydration

In the context of climate change and the reduction of mineral nitrogen (N) inputs applied to the field, winter oilseed rape (WOSR) will have to cope with low-N conditions combined with water limitation periods. Since these stresses can significantly reduce seed yield and seed quality, maintaining WOSR productivity under a wide range of growth conditions represents a major goal for crop improvement. N metabolism plays a pivotal role during the metabolic acclimation to drought in Brassica species by supporting the accumulation of osmoprotective compounds and the source-to-sink remobilization of nutrients. Thus, N deficiency could have detrimental effects on the acclimation of WOSR to drought. Here, we took advantage of a previously established experiment to evaluate the metabolic acclimation of WOSR during 14 days of drought, followed by 8 days of rehydration under high- or low-N fertilization regimes. For this purpose, we selected three leaf ranks exhibiting contrasted sink/source status to perform absolute quantification of plant central metabolites. Besides the well-described accumulation of proline, we observed contrasted accumulations of some "respiratory" amino acids (branched-chain amino acids, lysineand tyrosine) in response to drought under high- and low-N conditions. Drought also induced an increase in sucrose content in sink leaves combined with a decrease in source leaves. N deficiency strongly decreased the levels of major amino acids and subsequently the metabolic response to drought. The drought-rehydration sequence identified proline, phenylalanine, and tryptophan as valuable metabolic indicators of WOSR water status for sink leaves. The results were discussed with respect to the metabolic origin of sucrose and some amino acids in sink leaves and the impact of drought on source-to-sink remobilization processes depending on N nutrition status. Overall, this study identified major metabolic signatures reflecting a similar response of oilseed rape to drought under low- and high-N conditions.

Comparative analysis of wild-type and chloroplast MCU-deficient plants reveals multiple consequences of chloroplast calcium handling under drought stress

Introduction

Chloroplast calcium homeostasis plays an important role in modulating the response of plants to abiotic and biotic stresses. One of the greatest challenges is to understand how chloroplast calcium-permeable pathways and sensors are regulated in a concerted manner to translate specific information into a calcium signature and to elucidate the downstream effects of specific chloroplast calcium dynamics. One of the six homologs of the mitochondrial calcium uniporter (MCU) was found to be located in chloroplasts in the leaves and to crucially contribute to drought- and oxidative stress-triggered uptake of calcium into this organelle.

Methods

In the present study we integrated comparative proteomic analysis with biochemical, genetic, cellular, ionomic and hormone analysis in order to gain an insight into how chloroplast calcium channels are integrated into signaling circuits under watered condition and under drought stress.

Results

Altogether, our results indicate for the first time a link between chloroplast calcium channels and hormone levels, showing an enhanced ABA level in the cmcu mutant already in well-watered condition. Furthermore, we show that the lack of cMCU results in an upregulation of the calcium sensor CAS and of enzymes of chlorophyll synthesis, which are also involved in retrograde signaling upon drought stress, in two independent KO lines generated in Col-0 and Col-4 ecotypes.

Conclusions

These observations point to chloroplasts as important signaling hubs linked to their calcium dynamics. Our results obtained in the model plant Arabidopsis thaliana are discussed also in light of our limited knowledge regarding organellar calcium signaling in crops and raise the possibility of an involvement of such signaling in response to drought stress also in crops.

Metabolomics and Transcriptomics Analyses Reveals the Molecular Regulatory Mechanisms of Walnut (Juglans regia L.) Embryos in Response to Shade Treatment

The walnut is an important nut that has numerous uses worldwide. However, due to dwarf and close plantation methods as well as continuous cloudy or rainy days that occur during periods of walnut oil accumulation, the walnut fruit exhibits varying degrees of stress under low-light conditions. However, the effects of shade on metabolites and genes in walnut embryos remain unclear in the literature. The purpose of this study is to investigate the lipid biosynthesis process that occurs in walnut embryos under shade treatment via the use of metabolomics and transcriptomics analyses. The results indicate that the oil content decreases significantly under shaded conditions, while the protein content increases significantly. The expression levels of fatty acid desaturase 2 (FAD2) and stearoyl-ACP-desaturase (SAD) involved in the lipid biosynthesis mechanism were significantly reduced in the shaded group, which resulted in reductions in oleic (C18:1), linoleic (C18:2), and α-linolenic (C18:3) acids. The reduced oil content was consistent with the downregulation of genes associated with the lipid biosynthesis mechanism. In the amino acid biosynthesis process, the upregulated cysteine synthase (cscK) and anthranilate synthase beta subunit 2 (trpG) genes promoted the accumulation of L-aspartic acid and L-citrulline. The increase in protein content was consistent with the upregulation of genes related to amino acid biosynthesis. Thus, our study provides new insights into the regulatory mechanisms of shade underlying overall walnut fruit quality.

Transcriptomic and Metabolomic Analyses Reveal That Fullerol Improves Drought Tolerance in Brassica napus L

Carbon nanoparticles have potential threats to plant growth and stress tolerance. The polyhydroxy fullerene-fullerol (one of the carbon nanoparticles) could increase biomass accumulation in several plants subjected to drought; however, the underlying molecular and metabolic mechanisms governed by fullerol in improving drought tolerance in Brassica napus remain unclear. In the present study, exogenous fullerol was applied to the leaves of B. napus seedlings under drought conditions. The results of transcriptomic and metabolomic analyses revealed changes in the molecular and metabolic profiles of B. napus. The differentially expressed genes and the differentially accumulated metabolites, induced by drought or fullerol treatment, were mainly enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to carbohydrate metabolism (e.g., "carbon metabolism" and "galactose metabolism"), amino acid metabolism (e.g., "biosynthesis of amino acids" and "arginine and proline metabolism"), and secondary metabolite metabolism (e.g., "biosynthesis of secondary metabolites"). For carbohydrate metabolism, the accumulation of oligosaccharides (e.g., sucrose) was decreased, whereas that of monosaccharides (e.g., mannose and myo-inositol) was increased by drought. With regard to amino acid metabolism, under drought stress, the accumulation of amino acids such as phenylalanine and tryptophan decreased, whereas that of glutamate and proline increased. Further, for secondary metabolite metabolism, B. napus subjected to soil drying showed a reduction in phenolics and flavonoids, such as hyperoside and trans-3-coumaric acid. However, the accumulation of carbohydrates was almost unchanged in fullerol-treated B. napus subjected to drought. When exposed to water shortage, the accumulation of amino acids, such as proline, was decreased upon fullerol treatment. However, that of phenolics and flavonoids, such as luteolin and trans-3-coumaric acid, was enhanced. Our findings suggest that fullerol can alleviate the inhibitory effects of drought on phenolics and flavonoids to enhance drought tolerance in B. napus.

The Transcriptome and Metabolome Reveal the Potential Mechanism of Lodging Resistance in Intergeneric Hybrids between Brassica napus and Capsella bursa-pastoris

Lodging is one of the main reasons for the reduction in seed yield and is the limitation of mechanized harvesting in B. napus. The dissection of the regulatory mechanism of lodging resistance is an important goal in B. napus. In this study, the lodging resistant B. napus line, YG689, derived from the hybridization between B. napus cv. Zhongyou 821 (ZY821) and Capsella bursa-pastoris, was used to dissect the regulation mechanism of hard stem formation by integrating anatomical structure, transcriptome and metabolome analyses. It was shown that the lignocellulose content of YG689 is higher than that of ZY821, and some differentially expressed genes (DEGs) involved in the lignocellulose synthesis pathway were revealed by transcriptome analyses. Meanwhile, GC–TOF–MS and UPLC–QTOF–MS identified 40, 54, and 31 differential metabolites in the bolting stage, first flower stage, and the final flower stage. The differential accumulation of these metabolites might be associated with the lignocellulose biosynthesis in B. napus. Finally, some important genes that regulate the metabolic pathway of lignocellulose biosynthesis, such as BnaA02g18920D, BnaA10g15590D, BnaC05g48040D, and NewGene_216 were identified in B. napus through the combination of transcriptomics and metabolomics data. The present results explored the potential regulatory mechanism of lignocellulose biosynthesis, which provided a new clue for the breeding of B. napus with lodging resistance in the future.