Glycine betaine biosynthesis in saltbushes (Atriplex spp.) under salinity stress

Analysis of N6-methyladenosine reveals a new important mechanism regulating the salt tolerance of sugar beet (Beta vulgaris)

Salinity is an important environmental factor in crop growth and development. N6-methyladenosine (m6A) is an essential epigenetic modification that regulates plant-environment interaction. Sugar beet is a major sugar-yielding crop that has a certain tolerance to salt, but the dynamic response elicited by the m6A modification of transcripts under salt stress remains unknown. In this study, sugar beet was exposed to 300 mM NaCl to investigate its physiological response to high salinity and transcriptome-wide m6A modification profile. After the salt treatment, 7737 significantly modified m6A sites and 4981 differentially expressed genes (DEGs) were identified. Among the 312 m6A-modified DEGs, 113 hypomethylated DEGs were up-regulated and 99 hypermethylated DEGs were down-regulated, indicating a negative correlation between m6A modification and gene expression. Well-known salt tolerance genes (e.g., sodium/hydrogen exchanger 1, choline monooxygenase, and nucleoredoxin 2) and phospholipid signaling pathway genes (phosphoinositol-specific phospholipase C, phospholipase D, diacylglycerol kinase 1, etc.) were also among the m6A-modified genes. Further analysis showed that m6A modification may regulate salt-tolerant related gene expression by controlling mRNA stability. Therefore, changes in m6A modification may negatively regulate the expression of the salt-resistant genes in sugar beet, at least in part by modulating the stability of the mRNA via demethylase BvAlkbh10B. These findings could provide a better understanding of the epigenetic mechanisms of salt tolerance in sugar beets and uncover new candidate genes for improving the production of sugar beets planted in high-salinity soil.

Improved salt-tolerance of transgenic soybean by stable over-expression of AhBADH gene from Atriplex hortensis

KEY MESSAGE

The salt-tolerance of transgenic soybean cleared for environmental release was improved by stable over-expression of AhBADH gene from Atriplex hortensis, which was demonstrated through molecular analysis and field experiments. An effective strategy for increasing the productivity of major crops under salt stress conditions is the development of transgenics that harbor genes responsible for salinity tolerance. Betaine aldehyde dehydrogenase (BADH) is a key enzyme involved in the biosynthesis of the osmoprotectant, glycine betaine (GB), and osmotic balance in plants, and several plants transformed with BADH gene have shown significant improvements in salt tolerance. However, very few field-tested transgenic cultivars have been reported, as most of the transgenic studies are limited to laboratory or green house experiments. In this study, we demonstrated through field experiments that AhBADH from Atriplex hortensis confers salt tolerance when transformed into soybean (Glycine max L.). AhBADH was successfully introduced into soybean by Agrobacterium mediated transformation. A total of 256 transgenic plants were obtained, out of which 47 lines showed significant enhancement of salt tolerance compared to non-transgenic control plants. Molecular analyses of the transgenic line TL2 and TL7 with the highest salt tolerance exhibited stable inheritance and expression of AhBADH in progenies with a single copy insertion. TL1, TL2 and TL7 exhibited stable enhanced salt tolerance and improved agronomic traits when subjected to 300mM NaCl treatment. Currently, the transgenic line TL2 and TL7 with stable enhanced salt tolerance, which have been cleared for environmental release, are under biosafety assessment. TL 2 and TL7 stably expressing AhBADH could then be applied in commercial breeding experiments to genetically improve salt tolerance in soybean.

Transcriptome and Metabolome Analyses Revealed the Response Mechanism of Sugar Beet to Salt Stress of Different Durations

Salinity is one of the most serious threats to agriculture worldwide. Sugar beet is an important sugar-yielding crop and has a certain tolerance to salt; however, the genome-wide dynamic response to salt stress remains largely unknown in sugar beet. In the present study, physiological and transcriptome analyses of sugar beet leaves and roots were compared under salt stress at five time points. The results showed that different salt stresses influenced phenotypic characteristics, leaf relative water content and root activity in sugar beet. The contents of chlorophyll, malondialdehyde (MDA), the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were also affected by different salt stresses. Compared with control plants, there were 7391 and 8729 differentially expressed genes (DEGs) in leaves and roots under salt stress, respectively. A total of 41 hub genes related to salt stress were identified by weighted gene co-expression network analysis (WGCNA) from DEGs, and a transcriptional regulatory network based on these genes was constructed. The expression pattern of hub genes under salt stress was confirmed by qRT-PCR. In addition, the metabolite of sugar beet was compared under salt stress for 24 h. A total of 157 and 157 differentially accumulated metabolites (DAMs) were identified in leaves and roots, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further indicated that DEGs and DAMs act on the starch and sucrose metabolism, alpha-linolenic acid metabolism, phenylpropanoid biosynthesis and plant hormone signal transduction pathway. In this study, RNA-seq, WGCNA analysis and untargeted metabolomics were combined to investigate the transcriptional and metabolic changes of sugar beet during salt stress. The results provided new insights into the molecular mechanism of sugar beet response to salt stress, and also provided candidate genes for sugar beet improvement.

Whole-Transcriptome RNA Sequencing Reveals the Global Molecular Responses and CeRNA Regulatory Network of mRNAs, lncRNAs, miRNAs and circRNAs in Response to Salt Stress in Sugar Beet (Beta vulgaris)

Sugar beet is an important sugar-yielding crop with some tolerance to salt, but the mechanistic basis of this tolerance is not known. In the present study, we have used whole-transcriptome RNA-seq and degradome sequencing in response to salt stress to uncover differentially expressed (DE) mRNAs, microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) in both leaves and roots. A competitive endogenous RNA (ceRNA) network was constructed with the predicted DE pairs, which revealed regulatory roles under salt stress. A functional analysis suggests that ceRNAs are implicated in copper redistribution, plasma membrane permeability, glycometabolism and energy metabolism, NAC transcription factor and the phosphoinositol signaling system. Overall, we conducted for the first time a full transcriptomic analysis of sugar beet under salt stress that involves a potential ceRNA network, thus providing a basis to study the potential functions of lncRNAs/circRNAs.

Evaluation of Diverse Barley Cultivars and Landraces for Contents of Four Multifunctional Biomolecules with Nutraceutical Potential

Barley is long-identified as a functional food due to its content of micronutrients, β-glucans and vitamins. However, there is scant literature on a number of other nutritionally important biomolecules in the barley grain. This study determined the contents of four biomolecules, each with multiple known human and/or other animal health benefits, in the grains of 27 commercial barley cultivars and 7 landraces of barley from diverse countries of origin. These included the antioxidants, comprised of various vitamin E isomers and polyphenols, the osmoprotectant glycine betaine (GB) that protects cellular cytoplasm from osmotic shock, and the ‘plant stress hormone’ abscisic acid (ABA) which is endogenously expressed in humans and has multiple roles in physiology. All grains exhibited the presence of all biomolecules, suggesting they could potentially make some contribution to the health benefits of barley. The total vitamin E content varied between 19.20 - 54.56 μg/g DW, with α-tocotrienol being the major component (33.9 - 60.7%). The phenolics made up 3.21 - 9.73 mg gallic acid equivalent (GAE)/g DW, exceeding the amounts in the two major cereals, rice and wheat. GB ranged between 0.41-1.40 mg/g DW. The total vitamin E contents and GB typically exceeded those in corn. ABA ranged as 8.50 - 235.46 ng/g dry weight (DW), with the highest inter-variety variability. The data confirm barley to be an excellent source of these nutraceuticals, generally better than other major cereals. Our results thus offer more detailed insights into the potential of barley as a functional food and suggests the need to investigate in depth the health effects of this grain as well as the contribution of genetic and environmental factors.

iTRAQ protein profile analysis of sugar beet under salt stress: different coping mechanisms in leaves and roots

BACKGROUND

Salinity is one of the most serious threats to world agriculture. An important sugar-yielding crop sugar beet, which shows some tolerance to salt via a mechanism that is poorly understood. Proteomics data can provide important clues that can contribute to finally understand this mechanism.

RESULTS

Differentially abundant proteins (DAPs) in sugar beet under salt stress treatment were identified in leaves (70 DAPs) and roots (76 DAPs). Functions of these DAPs were predicted, and included metabolism and cellular, environmental information and genetic information processing. We hypothesize that these processes work in concert to maintain cellular homeostasis. Some DAPs are closely related to salt resistance, such as choline monooxygenase, betaine aldehyde dehydrogenase, glutathione S-transferase (GST) and F-type H+-transporting ATPase. The expression pattern of ten DAPs encoding genes was consistent with the iTRAQ data.

CONCLUSIONS

During sugar beet adaptation to salt stress, leaves and roots cope using distinct mechanisms of molecular metabolism regulation. This study provides significant insights into the molecular mechanism underlying the response of higher plants to salt stress, and identified some candidate proteins involved in salt stress countermeasures.

Bona fide choline monoxygenases evolved in Amaranthaceae plants from oxygenases of unknown function: Evidence from phylogenetics, homology modeling and docking studies

Few land plants can synthesize and accumulate the osmoprotectant glycine betaine (GB) even though this metabolic trait has major adaptive importance given the prevalence of drought, hypersaline soils or cold. GB is synthesized from choline in two reactions catalyzed by choline monooxygenases (CMOs) and enzymes of the family 10 of aldehyde dehydrogenases (ALDH10s) that gained betaine aldehyde dehydrogenase activity (BADH). Homolog genes encoding CMO and ALDH10 enzymes are present in all known land plant genomes, but since GB-non-accumulators plants lack the BADH-type ALDH10 isozyme, they would be expected to also lack the CMO activity to avoid accumulation of the toxic betaine aldehyde. To explore CMOs substrate specificity, we performed amino acid sequence alignments, phylogenetic analysis, homology modeling and docking simulations. We found that plant CMOs form a monophyletic subfamily within the Rieske/mononuclear non-heme oxygenases family with two clades: CMO1 and CMO2, the latter diverging from CMO1 after gene duplication. CMO1 enzymes are present in all plants; CMO2s only in the Amaranthaceae high-GB-accumulators plants. CMO2s, and particularly their mononuclear non-heme iron domain where the active site is located, evolved at a faster rate than CMO1s, which suggests positive selection. The homology model and docking simulations of the spinach CMO2 enzyme showed at the active site three aromatic residues forming a box with which the trimethylammonium group of choline could interact through cation-π interactions, and a glutamate, which also may interact with the trimethylammonium group through a charge-charge interaction. The aromatic box and the carboxylate have been shown to be critical for choline binding in other proteins. Interestingly, these residues are conserved in CMO2 proteins but not in CMO1 proteins, where two of these aromatic residues are leucine and the glutamate is asparagine. These findings reinforce our proposal that the CMO1s physiological substrate is not choline but a still unknown metabolite.

Molecular cloning and expression analysis of two key genes, HDS and HDR, in the MEP pathway in Pyropia haitanensis

The 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase (HDS) gene and the 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase (HDR) gene are two important genes in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. In this study, we reported the isolation and characterization of full-length HDS (MF101802) and HDR (MF159558) from Pyropia haitanensis. Characteristics of 3-D structures of the PhHDS and PhHDR proteins were analysed respectively. The results showed that the full-length cDNA of PhHDS, which is 1801 bp long, contained a 1455 bp open reading frame (ORF) encoding a putative 484 amino acid residue protein with a predicted molecular mass of 51.60 kDa. Meanwhile, the full-length cDNA of PhHDR was 1668 bp and contained a 1434 bp ORF encoding a putative 477 amino acid 2 residue protein with a predicted molecular mass of 51.49 kDa. The expression levels of the two genes were higher in conchocelis than that in leafy thallus. Additionally, the expression levels could be influenced by light, temperature and salinity and induced by methyl jasmonate (MJ) and salicylic acid (SA). This study contributed to our in-depth understanding of the roles of PhHDS and PhHDR in terpenoid biosynthesis in Pyropia haitanensis and the regulation of the two genes by external environments.

Exploring the evolutionary route of the acquisition of betaine aldehyde dehydrogenase activity by plant ALDH10 enzymes: implications for the synthesis of the osmoprotectant glycine betaine

BACKGROUND

Plant ALDH10 enzymes are aminoaldehyde dehydrogenases (AMADHs) that oxidize different ω-amino or trimethylammonium aldehydes, but only some of them have betaine aldehyde dehydrogenase (BADH) activity and produce the osmoprotectant glycine betaine (GB). The latter enzymes possess alanine or cysteine at position 441 (numbering of the spinach enzyme, SoBADH), while those ALDH10s that cannot oxidize betaine aldehyde (BAL) have isoleucine at this position. Only the plants that contain A441- or C441-type ALDH10 isoenzymes accumulate GB in response to osmotic stress. In this work we explored the evolutionary history of the acquisition of BAL specificity by plant ALDH10s.

RESULTS

We performed extensive phylogenetic analyses and constructed and characterized, kinetically and structurally, four SoBADH variants that simulate the parsimonious intermediates in the evolutionary pathway from I441-type to A441- or C441-type enzymes. All mutants had a correct folding, average thermal stabilities and similar activity with aminopropionaldehyde, but whereas A441S and A441T exhibited significant activity with BAL, A441V and A441F did not. The kinetics of the mutants were consistent with their predicted structural features obtained by modeling, and confirmed the importance of position 441 for BAL specificity. The acquisition of BADH activity could have happened through any of these intermediates without detriment of the original function or protein stability. Phylogenetic studies showed that this event occurred independently several times during angiosperms evolution when an ALDH10 gene duplicate changed the critical Ile residue for Ala or Cys in two consecutive single mutations. ALDH10 isoenzymes frequently group in two clades within a plant family: one includes peroxisomal I441-type, the other peroxisomal and non-peroxisomal I441-, A441- or C441-type. Interestingly, high GB-accumulators plants have non-peroxisomal A441- or C441-type isoenzymes, while low-GB accumulators have the peroxisomal C441-type, suggesting some limitations in the peroxisomal GB synthesis.

CONCLUSION

Our findings shed light on the evolution of the synthesis of GB in plants, a metabolic trait of most ecological and physiological relevance for their tolerance to drought, hypersaline soils and cold. Together, our results are consistent with smooth evolutionary pathways for the acquisition of the BADH function from ancestral I441-type AMADHs, thus explaining the relatively high occurrence of this event.

Rendimentos de carcaça, cortes comerciais e não-componentes da carcaça de cordeiros Santa Inês alimentados com feno de erva-sal e concentrado

Objetivou-se com este trabalho avaliar os rendimentos de carcaça, cortes comerciais e não-componentes da carcaça de cordeiros Santa Inês alimentados com 30, 40, 50 e 60% de feno de erva-sal associado a concentrado. Foram utilizados 32 ovinos machos castrados, com 8 meses de idade e peso inicial de 22 + 1,97kg, confinados individualmente e abatidos após 60 dias de confinamento. Os pesos de carcaça quente e fria decresceram linearmente com o aumento de feno de erva-sal na dieta, no entanto, não houve efeito para o rendimento verdadeiro de carcaça (59,42%) e dos cortes: paleta (19,26%), pescoço (8,52%), costelas (26,57%) e perna (33,88%). Houve efeito linear decrescente para área de olho de lombo e espessura de gordura à medida que o nível de feno de erva-sal aumentou na dieta. Os pesos e os rendimentos de pele, fígado, coração, rins com gordura perirrenal e gorduras omental e mesentérica decresceram linearmente com a inclusão de feno de erva-sal na dieta, enquanto o conteúdo (%) do trato gastrintestinal aumentou. O aumento da proporção de feno de erva-sal na dieta de cordeiros proporciona adequados rendimentos verdadeiros de carcaça e dos cortes comerciais, no entanto, reduz a área de olho de lombo e a espessura de gordura subcutânea, medidas importantes na avaliação qualitativa da carcaça ovina.