Multiple Regulatory Networks Are Activated during Cold Stress in Medicago sativa L

In silico analysis identified bZIP transcription factors genes responsive to abiotic stress in Alfalfa (Medicago sativa L.)

BACKGROUND

Alfalfa (Medicago sativa L.) is the most cultivated forage legume around the world. Under a variety of growing conditions, forage yield in alfalfa is stymied by biotic and abiotic stresses including heat, salt, drought, and disease. Given the sessile nature of plants, they use strategies including, but not limited to, differential gene expression to respond to environmental cues. Transcription factors control the expression of genes that contribute to or enable tolerance and survival during periods of stress. Basic-leucine zipper (bZIP) transcription factors have been demonstrated to play a critical role in regulating plant growth and development as well as mediate the responses to abiotic stress in several species, including Arabidopsis thaliana, Oryza sativa, Lotus japonicus and Medicago truncatula. However, there is little information about bZIP transcription factors in cultivated alfalfa.

RESULT

In the present study, 237 bZIP genes were identified in alfalfa from publicly available sequencing data. Multiple sequence alignments showed the presence of intact bZIP motifs in the identified sequences. Based on previous phylogenetic analyses in A. thaliana, alfalfa bZIPs were similarly divided and fell into 10 groups. The physico-chemical properties, motif analysis and phylogenetic study of the alfalfa bZIPs revealed high specificity within groups. The differential expression of alfalfa bZIPs in a suite of tissues indicates that bZIP genes are specifically expressed at different developmental stages in alfalfa. Similarly, expression analysis in response to ABA, cold, drought and salt stresses, indicates that a subset of bZIP genes are also differentially expressed and likely play a role in abiotic stress signaling and/or tolerance. RT-qPCR analysis on selected genes further verified these differential expression patterns.

CONCLUSIONS

Taken together, this work provides a framework for the future study of bZIPs in alfalfa and presents candidate bZIPs involved in stress-response signaling.

Antagonistic activity and mechanism of Bacillus subtilis CG-6 suppression of root rot and growth promotion in Alfalfa

Root rot is a common disease, that severely affects the yield and quality of alfalfa. Biocontrol is widely used to control plant diseases caused by pathogenic fungi, however, biocontrol strains for alfalfa root rot are very limited. In this study, a Bacillus subtilis CG-6 strain with a significant biocontrol effect on alfalfa root rot was isolated. CG-6 secretes antibacterial enzymes and siderophore, phosphate solubilization and indoleacetic acid (IAA). The inhibition rate of strain CG-6 against Fusarium oxysporum was 87.33%, and it showed broad-spectrum antifungal activity. Inoculation with CG-6 significantly reduced the incidence of alfalfa root rot, the control effect of greenhouse cultivation reached 58.12%, and CG-6 treatment significantly increased alfalfa plant height, root length, fresh weight, and dry weight. The treatment with CG-6 significantly increased the levels of antioxidant enzymes (catalase, peroxidase, superoxide dismutase, and lipoxygenase) in alfalfa leaves by 15.52%-34.03%. Defensive enzymes (chitinase and β-1,3-glucanase) increased by 24.37% and 28.08%, respectively. The expression levels of regulatory enzyme genes (MsCAT, MsPOD, MsCu, Zn-SOD1, MsCu, Zn-SOD2, MsCu, Zn-SOD3, and MsLOX2) and systemic resistance genes (MsPR1, MsPDF1.2, and MsVSP2) increased by 0.50-2.85 fold, which were higher than those in the pathogen treatment group. Therefore, CG-6 could be used as a potential strain to develop biopesticides against alfalfa root rot.

MODMS: a multi-omics database for facilitating biological studies on alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.) is a globally important forage crop. It also serves as a vegetable and medicinal herb because of its excellent nutritional quality and significant economic value. Multi-omics data on alfalfa continue to accumulate owing to recent advances in high-throughput techniques, and integrating this information holds great potential for expediting genetic research and facilitating advances in alfalfa agronomic traits. Therefore, we developed a comprehensive database named MODMS (multi-omics database of M. sativa) that incorporates multiple reference genomes, annotations, comparative genomics, transcriptomes, high-quality genomic variants, proteomics, and metabolomics. This report describes our continuously evolving database, which provides researchers with several convenient tools and extensive omics data resources, facilitating the expansion of alfalfa research. Further details regarding the MODMS database are available at https://modms.lzu.edu.cn/.

Identification and evolution analysis of YUCCA genes of Medicago sativa and Medicago truncatula and their expression profiles under abiotic stress

The YUCCAs (YUC) are functionally identified flavin-containing monooxidases (FMOs) in plants that act as an important rate-limiting enzyme functioning in the auxin synthesis IPA (indole-3-pyruvic acid) pathway. In this study, 12 MsYUCs and 15 MtYUCs containing characteristic conserved motifs were identified in M. sativa (Medicago sativa L.) and M. truncatula (Medicago truncatula Gaertn.), respectively. Phylogenetic analysis revealed that YUC proteins underwent an evolutionary divergence. Both tandem and segmental duplication events were presented in MsYUC and MtYUC genes. Comparative syntenic maps of M. sativa with M. truncatula, Arabidopsis (Arabidopsis thaliana), or rice (Oryza sativa L.) were constructed to illustrate the evolution relationship of the YUC gene family. A large number of cis-acting elements related to stress response and hormone regulation were revealed in the promoter sequences of MsYUCs. Expression analysis showed that MsYUCs had a tissue-specific, genotype-differential expression and a differential abiotic stress response pattern based on transcriptome data analysis of M. sativa online. In addition, RT-qPCR confirmed that salt stress significantly induced the expression of MsYUC1/MsYUC10 but significantly inhibited MsYUC2/MsYUC3 expression and the expression of MsYUC10/MsYUC11/MsYUC12 was significantly induced by cold treatment. These results could provide valuable information for functional analysis of YUC genes via gene engineering of the auxin synthetic IPA pathway in Medicago.

Transcriptome Analysis Reveals Brassinolide Signaling Pathway Control of Foxtail Millet Seedling Starch and Sucrose Metabolism under Freezing Stress, with Implications for Growth and Development

Low-temperature stress limits the growth and development of foxtail millet. Freezing stress caused by sudden temperature drops, such as late-spring coldness, often occurs in the seedling stage of foxtail millet. However, the ability and coping strategies of foxtail millet to cope with such stress are not clear. In the present study, we analyzed the self-regulatory mechanisms of freezing stress in foxtail millet. We conducted a physiological study on foxtail millet leaves at -4 °C for seven different durations (0, 2, 4, 6, 8, 10, and 12 h). Longer freezing time increased cell-membrane damage, relative conductance, and malondialdehyde content. This led to osmotic stress in the leaves, which triggered an increase in free proline, soluble sugar, and soluble protein contents. The increases in these substances helped to reduce the damage caused by stress. The activities of superoxide dismutase, peroxidase, and catalase increased reactive oxygen species (ROS) content. The optimal time point for the response to freezing stress was 8 h after exposure. The transcriptome analysis of samples held for 8 h at -4 °C revealed 6862 differentially expressed genes (DEGs), among which the majority are implicated in various pathways, including the starch and sucrose metabolic pathways, antioxidant enzyme pathways, brassinolide (BR) signaling pathway, and transcription factors, according to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. We investigated possible crosstalk between BR signals and other pathways and found that BR signaling molecules were induced in response to freezing stress. The beta-amylase (BAM) starch hydrolase signal was enhanced by the BR signal, resulting in the accelerated degradation of starch and the formation of sugars, which served as emerging ROS scavengers and osmoregulators to resist freezing stress. In conclusion, crosstalk between BR signal transduction, and both starch and sucrose metabolism under freezing stress provides a new perspective for improving freezing resistance in foxtail millet.

Genome-wide identification and expression analysis of DREB genes in alfalfa (Medicago sativa) in response to cold stress

Dehydration-responsive element-binding proteins (DREBs) belong to members of the AP2/ERF transcription factor superfamily, which has been reported to involve various abiotic-stress responses and tolerance in plants. However, research on the DREB-family is still limited in alfalfa (Medicago sativa L.), a forage legume cultivated worldwide. The recent genome-sequence release of the alfalfa cultivar "XinJiangDaYe" allowed us to identify 172 DREBs by a multi-step homolog search. The phylogenetic analysis indicated that such MsDREBs could be classified into 5 groups, namely A-1 (56 members), A-2 (39), A-3 (3), A-4 (61) and 13 (A-5 (13), thus adding substantial new members to the DREB-family in alfalfa. Furthermore, a comprehensive survey in silico of conserved motif, gene structure, molecular weight, and isoelectric point (pI) as well as gene expression was conducted. The resulting data showed that, for cold-stress response, 33 differentially expressed MsDREBs were identified with a threshold of Log2-fold > 1, and most of which were transcriptionally upregulated within 48 h during a cold treatment(s). Moreover, the expression profiling of MsDREBs from two ecotypes of alfalfa subspecies i.e. M. sativa ssp. falcata (F56, from a colder region of Central Asia) and M. sativa ssp. sativa (B47, from Near East) revealed that most of the cold-stress responsive MsDREBs exhibited a significantly lower expression in F56, leading to a proposal of the existence of a distinct mechanism(s) for cold tolerance regulated by DREB-related action, which would have been evolved in alfalfa with a genotypic specificity. Additionally, by examining the transcriptome of a freezing-tolerance species (M. sativa cv. Zhaodong), eight DREBs were found to be implicated in a long-term freezing-stress adaptation with a great potential. Taken together, the current genome-wide identification in alfalfa points to the importance of some MsDREBs in the cold-stress response, providing some promising molecular targets to be functionally characterized for the improvement of cold tolerance in crops including alfalfa.

Genome-Wide Identification of bHLH Transcription Factor in Medicago sativa in Response to Cold Stress

Alfalfa represents one of the most important legume forages, and it is also applied as an organic fertilizer to improve soil quality. However, this perennial plant is native to warmer temperate regions, and its valuable cold-acclimation-related regulatory mechanisms are still less known. In higher plants, the bHLH transcription factors play pleiotropic regulatory roles in response to abiotic stresses. The recently released whole genome sequencing data of alfalfa allowed us to identify 469 MsbHLHs by multi-step homolog search. Herein, we primarily identified 65 MsbHLH genes that significantly upregulated under cold stress, and such bHLHs were classified into six clades according to their expression patterns. Interestingly, the phylogenetic analysis and conserved motif screening of the cold-induced MsbHLHs showed that the expression pattern is relatively varied in each bHLH subfamily, this result indicating that the 65 MsbHLHs may be involved in a complex cold-responsive regulatory network. Hence, we analyzed the TFBSs at promoter regions that unraveled a relatively conserved TFBS distribution with genes exhibiting similar expression patterns. Eventually, to verify the core components involved in long-term cold acclimation, we examined transcriptome data from a freezing-tolerant species (cv. Zhaodong) in the field and compared the expression of cold-sensitive/tolerant subspecies of alfalfa, giving 11 bHLH as candidates, which could be important for further cold-tolerance enhancement and molecular breeding through genetic engineering in alfalfa.

Combining QTL mapping and RNA-Seq Unravels candidate genes for Alfalfa (Medicago sativa L.) leaf development

BACKGROUND

Leaf size affects crop canopy morphology and photosynthetic efficiency, which can influence forage yield and quality. It is of great significance to mine the key genes controlling leaf development for breeding new alfalfa varieties. In this study, we mapped leaf length (LL), leaf width (LW), and leaf area (LA) in an F1 mapping population derived from a cultivar named ZhongmuNo.1 with larger leaf area and a landrace named Cangzhou with smaller leaf area.

RESULTS

This study showed that the larger LW was more conducive to increasing LA. A total of 24 significant quantitative trait loci (QTL) associated with leaf size were identified on both the paternal and maternal linkage maps. Among them, nine QTL explained about 11.50-22.45% phenotypic variation. RNA-seq analysis identified 2,443 leaf-specific genes and 3,770 differentially expressed genes. Combining QTL mapping, RNA-seq alalysis, and qRT-PCR, we identified seven candidate genes associated with leaf development in five major QTL regions.

CONCLUSION

Our study will provide a theoretical basis for marker-assisted breeding and lay a foundation for further revealing molecular mechanism of leaf development in alfalfa.

Transcriptome analysis and identification of abscisic acid and gibberellin-related genes during seed development of alfalfa (Medicago sativa L.)

BACKGROUND

Alfalfa (Medicago sativa) is a widely cultivated plant. Unlike many crops, the main goal of breeding alfalfa is to increase its aboveground biomass rather than the biomass of its seeds. However, the low yield of alfalfa seeds limits alfalfa production. Many studies have explored the factors affecting seed development, in which phytohormones, especially ABA and GAs, play an important role in seed development.

RESULTS

Here, we performed a transcriptome analysis of alfalfa seeds at five development stages. A total of 16,899 differentially expressed genes (DEGs) were identified and classified into 10 clusters, and the enriched Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were determined. The contents of ABA, GA₁, GA₃, GA₄ and GA₇ in alfalfa seeds at five development stages were determined. In addition, 14 ABA-related DEGs and 20 GA-related DEGs were identified and analysed. These DEGs are involved in plant hormone pathways and play an important role in seed development. Moreover, morphological and physiological analyses revealed the dynamic changes during the development of alfalfa seeds.

CONCLUSION

Overall, our study is the first to analyse the transcriptome across various stages of seed development in alfalfa. The results of our study could be used to improve alfalfa seed yield. The key ABA and GA related-genes are potential targets for improving alfalfa seed yield via genetic engineering in the future.

Combination of Medium- and High-Pressure Liquid Chromatography for Isolation of L-tryptophan (Q-marker) from Medicago sativa Extract

Medicago sativa (alfalfa) is a widely used animal feed. However, its quality has been difficult to control due to the lack of appropriate marker compounds. Therefore, it is very necessary to select an appropriate quality marker (Q-marker) to control its quality. In this study, medium-pressure liquid chromatography and high-pressure liquid chromatography were employed to effectively prepare the separation of the Q-marker (L-tryptophan) from Medicago sativa. Firstly, using MCI GEL® CHP20P as the stationary phase, 2.5 g of the target fraction Fr3 was enriched from crude Medicago sativa extract (2.9 kg) by medium-pressure liquid chromatography. Secondly, Sephadex LH-20 was used to further separate Fr3 fractions, and the Fr34 fraction (358.3 mg) was enriched after 14 repetitions. Lastly, using the ReproSil-Pur C18 AQ preparative column, 63.4 mg of L-tryptophan was obtained by high-pressure liquid chromatography, and the purity was above 95%. The results showed that medium-pressure liquid chromatography (MCI GEL® CHP20P and Sephadex LH-20) combined with high-pressure liquid chromatography (ReproSil-Pur C18 AQ) could be used to effectively prepare the Q-marker from natural products with satisfactory purity.

Identification and Characterization of Regulatory Pathways Controlling Dormancy Under Lower Temperature in Alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.), a kind of high-quality perennial legume forage, is widely distributed in the northern regions of China. In recent years, low temperatures have frequently occurred and limited alfalfa productivity and survival in early spring and late fall. However, the underlying molecular mechanisms of alfalfa response to cold tolerance are not well-documented. In this study, dormancy and non-dormancy alfalfa standard varieties were characterized under low-temperature stress. Our analysis revealed that plant height of the dormancy genotype was strongly inhibited by low temperature; flavonoids content, and higher expression of flavonoids biosynthesis genes (chalcone synthase, leucoanthocyanidin dioxygenase, and flavonoid 3'-monooxygenase) may play essential roles in response to low-temperature stress in dormancy genotype alfalfa. Further analyses revealed that receptor-like kinase family genes (such as cysteine-rich RLK10, lectin protein kinase, and S-locus glycoprotein like kinase), RNA and protein synthesis genes (RNA polymerases, ribosomal protein, and protein phosphatase 2C family protein), and proteasome degradation pathway genes (such as F-box family protein, RING/U-box superfamily protein, and zinc finger family protein) also highly upregulated and contributed to cold tolerance phenotype in dormancy genotype alfalfa. This will provide new insights into future studies for cold tolerance in alfalfa and offer new target genes for further functional characterization and genetic improvement of alfalfa.

Non-targeted Metabolomics Analysis Based on LC–MS to Assess the Effects of Different Cold Exposure Times on Piglets

Pigs are susceptible to low temperature conditions, and cold stress causes metabolic changes in the body to increase heat production as an adaption to adverse environments. To characterize and validate different metabolites in piglet livers at different cold exposure times, sixteen 30-day-old male weaned piglets with similar weights were randomly divided into four groups: the normal temperature group (24 ± 2°C, NT) and cold exposure (4 ± 2°C) 2-h group (CS2), 6-h group (CS6), and 12-h group (CS12). At the end of the experiment, the liver samples were analyzed using systemic non-targeted metabolomics. Eight known differentially abundant metabolites (farnesyl pyrophosphate, isocitrate, triethanolamine, phenylethylamine, deoxynosine, citric acid, maltotriose, and epinephrine) were observed between the CS groups and the control group in positive and negative ion modes. The eight main differentially abundant metabolites involved in seven metabolite classifications. Metabolic pathways and enrichment analyses revealed that the pathways involved three KEGG pathway classifications. Most of the pathways were related to amino acid or energy metabolism. Moreover, the metabolic pathways were not identical under different cold exposure times, with those following 2 and 6 h of cold exposure more related to carbohydrates and energy production and those following 12 h of cold exposure more related to the metabolism connected with epinephrine. Thus, under different cold exposure times, the metabolite profiles and metabolic pathways differed.

Comparative Transcriptome Analysis Reveals New Insight of Alfalfa (Medicago sativa L.) Cultivars in Response to Abrupt Freezing Stress

Freezing stress is a major limiting environmental factor that affects the productivity and distribution of alfalfa (Medicago sativa L.). There is growing evidence that enhancing freezing tolerance through resistance-related genes is one of the most efficient methods for solving this problem, whereas little is known about the complex regulatory mechanism of freezing stress. Herein, we performed transcriptome profiling of the leaves from two genotypes of alfalfa, freezing tolerance "Gannong NO.3" and freezing-sensitive "WL326GZ" exposure to -10°C to investigate which resistance-related genes could improve the freezing tolerance. Our results showed that a total of 121,366 genes were identified, and there were 7,245 differentially expressed genes (DEGs) between the control and treated leaves. In particular, the DEGs in "Gannong NO.3" were mainly enriched in the metabolic pathways and biosynthesis of secondary metabolites, and most of the DEGs in "WL326GZ" were enriched in the metabolic pathways, the biosynthesis of secondary metabolites, and plant-pathogen interactions. Moreover, the weighted gene co-expression network analysis (WGCNA) showed that ATP-binding cassette (ABC) C subfamily genes were strongly impacted by freezing stress, indicating that ABCC8 and ABCC3 are critical to develop the freezing tolerance. Moreover, our data revealed that numerous Ca2+ signal transduction and CBF/DREB1 pathway-related genes were severely impacted by the freezing resistance, which is believed to alleviate the damage caused by freezing stress. Altogether, these findings contribute the comprehensive information to understand the molecular mechanism of alfalfa adaptation to freezing stress and further provide functional candidate genes that can adapt to abiotic stress.

Genome-Wide Identification of the Q-type C2H2 Transcription Factor Family in Alfalfa (Medicago sativa) and Expression Analysis under Different Abiotic Stresses

Q-type C2H2 zinc-finger protein (C2H2-ZFP) transcription factors are associated with many plant growth development and environmental stress responses. To date, there have been few analyses of the Q-type C2H2-ZFP gene family in alfalfa (Medicago sativa subsp. sativa). In this study, we identified 58 Q-type C2H2-ZFPs across the entire alfalfa genome, and the gene structure, motif composition, chromosomal mapping, and cis-regulatory elements were explored, as well as the expression profiles of specific tissues and the response under different abiotic stresses. According to their phylogenetic features, these 58 MsZFPs were divided into 12 subgroups. Synteny analysis showed that duplication events play a vital role in the expansion of the MsZFP gene family. The collinearity results showed that a total of 26 and 42 of the 58 MsZFP genes were homologous with Arabidopsis and M. truncatula, respectively. The expression profiles showed that C2H2-ZFP genes played various roles in different tissues and abiotic stresses. The results of subsequent quantitative real-time polymerase chain reaction (qRT-PCR) showed that the nine selected MsZFP genes were rapidly induced under different abiotic stresses, indicating that C2H2-ZFP genes are closely related to abiotic stress. This study provides results on MsZFP genes, their response to various abiotic stresses, and new information on the C2H2 family in alfalfa.

Changes in phenotype and gene expression under lead stress revealed key genetic responses to lead tolerance in Medicago sativa L

Lead (Pb) is a serious heavy metal soil pollutant. It can be absorbed and accumulated by plant roots and impact plant growth. Medicago sativa L. (alfalfa) is a low-input forage and potential bioenergy crop, and improving its yield and quality has always been a focus of the alfalfa breeding industry. Little is known about the mechanism by which alfalfa responds to Pb stress at the molecular level. In this study, three alfalfa genotypes (a lead-resistant type (LR), a lead-sensitive type (LS) and an intermediate type (IN)) with contrasting abilities to resist lead were exposed to different durations of Pb treatment. Next-generation sequencing (NGS)-based RNA-seq technology was employed to characterize the root transcriptomes of three genotypes of alfalfa and identify differentially expressed genes (DEGs) during Pb stress. Genotypes LR and LS displayed different mechanisms of tolerance. In LR, the accumulation of more resistant substances was induced by the upregulation of sucrose synthase, glucan endo-1,3-beta-glucosidase, beta-amylase 3, probable trehalose-phosphate phosphatase J, 6-phosphofructo-2-kinase delta-1-pyrroline-5-carboxylate synthase (P5CS) and δ-ornithine aminotransferase (δ-OAT). In addition, flavin monooxygenase (YUCCA), 4-coumarate:CoA ligase-like protein (4CL), cinnamoyl-CoA reductase-like protein (CCR), ferulate 5-hydroxylase (F5H) and caffeic acid O-methyltransferase (COMT) were upregulated, leading to root development in a short time under Pb stress. Further study of the expression levels of metal transport-related genes, such as NRAMP (metal transporter), MATE (multidrug and toxin extrusion), HIPPs (heavy metal-associated isoprenylated plant proteins), MTP (metal tolerance protein), and ABC transporter, suggested that these genes were differentially expressed after lead treatment in the three alfalfa genotypes. Our research provides useful information for further studies on the molecular mechanism of Pb resistance in Medicago sativa L.

WRKY Transcription Factors in Medicago sativa L.: Genome-Wide Identification and Expression Analysis Under Abiotic Stress

Alfalfa (Medicago sativa L.) is the most widely cultivated leguminous herb in the world. Its agricultural development has been restricted by various adverse environmental conditions, including water deficiency, high salinity, and low temperature. WRKY transcription factors (TFs) serve important roles in the regulation of plant development and stress responses. Research on the WRKY gene family has been reported for several species, but minimal information is available for alfalfa. In the present study, a total of 107 WRKY genes were identified in alfalfa and divided into 3 main groups. The classification, evolution, conserved motifs, and tissue expression were comprehensively analyzed. Meanwhile, 27 MsWRKY candidate genes that may be involved in abiotic stress were isolated through an analysis of gene expression profiles under different stresses, including cold, abscisic acid, drought, and salt treatments. Additionally, investigation of the cis-elements and potential biological functions of these genes further revealed that MsWRKY TFs may serve important roles in multiple stress resistance in alfalfa. This study provides an important foundation for future cloning and functional studies of WRKY genes in alfalfa.

Comparative transcriptomic analysis of resistant and susceptible tea cultivars in response to Empoasca onukii (Matsuda) damage

Transcriptomic studies in resistant and susceptible tea cultivars have been performed to reveal the different defense molecular mechanisms of tea after E. onukii feeding. The molecular mechanism by which tea plants respond to small green leafhopper Empoasca onukii (Matsuda) damage is unclear. Using the resistant tea plant cultivar Juyan (JY) and the susceptible tea plant cultivar Enbiao (EB) as materials, this study performed RNA-seq on tea leaf samples collected at three time points (6 h, 12 h, 24 h) during exposure of the plants to leafhopper to reveal the molecular mechanisms that are activated in susceptible and resistant tea plant cultivars in response to leafhopper damage. The numbers of DEGs in the susceptible tea cultivar during early (6 h) and late (24 h) stages of leafhopper induction were higher than those in the resistant cultivar at the same time points. The stress responses to leafhopper were most intense at 12 h in both tea cultivars. Pathway enrichment analysis showed that most up-regulated DEGs and their related metabolic pathways were similar in the two tea cultivars. However, during the early stage of leafhopper induction (6 h), jasmonic acid (JA)-related genes were significantly up-regulated in the resistant cultivar. The terpenoid biosynthetic pathway and the α-linolenic acid metabolic pathway were activated earlier in the resistant cultivar and remained activated until the late stage of leafhopper damage. Our results confirmed that after leafhopper damage, the resistant tea cultivar activated its defense responses earlier than the susceptible cultivar, and these defense responses were mainly related to terpenoid metabolism and JA biosynthetic pathway. The results provide important clues for further studies on resistance strategy of tea plants to pest.

Changes in carbohydrate metabolism and endogenous hormone regulation during bulblet initiation and development in Lycoris radiata

BACKGROUND

Lycoris species have great ornamental and medicinal values; however, their low regeneration efficiency seriously restricts their commercial production. Understanding the mechanism of bulblet propagation in this genus, which has remained underexplored to date, could provide a theoretical basis for improving the reproductive efficiency. Therefore, we studied the bulblet initiation and developmental processes in Lycoris radiata.

RESULTS

We found that bulblets are formed on the junctions of the innermost layers of scales and the basal plate, and initially present as an axillary bud and gradually develop into a bulblet. We also determined the changes in carbohydrate and endogenous hormone contents during bulblet initiation and development, as well as the expression patterns of genes involved in carbohydrate metabolism and hormone biosynthesis and signaling through transcriptome analysis. Soluble sugars derived from starch degradation in the outer scales are transported to and promote bulblet initiation and development through starch synthesis in the inner scales. This process is mediated by several genes involved in carbohydrate metabolism, especially genes encoding ADP glucose pyrophosphorylase, a crucial starch synthesis enzyme. As for hormones, endogenous IAA, GA, and ABA content showed an increase and decrease during bulblet initiation and development, respectively, which were consistent with the expression patterns of genes involved in IAA, GA, and ABA synthesis and signal transduction. In addition, a decrease in ZR content may be down- and up-regulated by CK biosynthesis and degradation related genes, respectively, with increasing auxin content. Furthermore, expression levels of genes related to BR, JA, and SA biosynthesis were increased, while that of ethylene biosynthesis genes was decreased, which was also consistent with the expression patterns of their signal transduction genes.

CONCLUSIONS

The present study provides insights into the effect of carbohydrate metabolism and endogenous hormone regulation on control of L. radiata bulblet initiation and development. Based on the results, we propose several suggestions to improve L. radiata propagation efficiency in production, which will provide directions for future research.

The uptake, effects and biotransformation of monepantel in meadow plants used as a livestock feed

Drugs are potentially dangerous environmental contaminants, as they are designed to have biological effects at low concentrations. Monepantel (MOP), an amino-acetonitrile derivative, is frequently used veterinary anthelmintics, but information about MOP environmental circulation and impact is almost non-existent. We studied the phytotoxicity, uptake and biotransformation of MOP in two fodder plants, Plantago lanceolata and Medicago sativa. The seeds and whole plant regenerants were cultivated with MOP. The plant roots and the leaves were collected after 1, 2, 3, 4, 5 and 6 weeks of cultivation. The lengths of roots and proline concentrations in the roots and leaves were measured to evaluate MOP phytotoxicity. The UHPLC-MS/MS technique with a Q-TOF mass analyser was used for the identification and semi-quantification of MOP and its metabolites. Our results showed no phytotoxicity of MOP. However, both plants were able to uptake, transport and metabolize MOP. Comparing both plants, the uptake of MOP was much more extensive in Medicago sativa (almost 10-times) than in Plantago lanceolate. Moreover, 9 various metabolites of MOP were detected in Medicago sativa, while only 7 MOP metabolites were found in Plantago lanceolata. Based on metabolites structures, scheme of the metabolic pathways of MOP in both plants was proposed. MOP and its main metabolite (MOP sulfone), both anthelmintically active, were present not only in roots but also in leaves that can be consumed by animals. This indicates the potential for undesirable circulation of MOP in the environment, which could lead to many pharmacological and toxicological consequences.

Asperpyridone A: An Unusual Pyridone Alkaloid Exerts Hypoglycemic Activity through the Insulin Signaling Pathway

A pyridone alkaloid, asperpyridone A (1), which possesses an unusual pyrano[3,2-c]pyridine scaffold, was isolated from solid cultures of the endophytic fungus Aspergillus sp. TJ23. Its structure, including its absolute configuration, was determined using a combination of nuclear magnetic resonance, high-resolution electrospray ionization mass spectrometry, quantum chemical calculations (electronic circular dichroism), and X-ray crystallography. In vitro bioassays demonstrated that asperpyridone A (1) could function as a potential hypoglycemic agent, which exhibited pronounced glucose uptake effect in liver HepG2 cells, under both normal and insulin-resistant conditions, with higher efficacy than metformin. The underlying mechanism of asperpyridone A was elucidated by analyzing the genes expressed, the Gene Ontology (GO) function enrichment, the protein interaction network, and real-time quantitative reverse transcription polymerase chain reaction, which suggested that asperpyridone A exhibits hypoglycemic activity by activating the insulin signaling pathway. Moreover, on the basis of the hypoglycemic potency, fibroblast growth factor 21 (FGF21) was determined to be a potential target for asperpyridone A.

MYB transcription factors in alfalfa (Medicago sativa): genome-wide identification and expression analysis under abiotic stresses

Background

Alfalfa is the most widely cultivated forage legume and one of the most economically valuable crops in the world. Its survival and production are often hampered by environmental changes. However, there are few studies on stress-resistance genes in alfalfa because of its incomplete genomic information and rare expression profile data. The MYB proteins are characterized by a highly conserved DNA-binding domain, which is large, functionally diverse, and represented in all eukaryotes. The role of MYB proteins in plant development is essential; they function in diverse biological processes, including stress and defense responses, and seed and floral development. Studies on the MYB gene family have been reported in several species, but they have not been comprehensively analyzed in alfalfa.

Methods

To identify more comprehensive MYB transcription factor family genes, the sequences of 168 Arabidopsis thaliana, 430 Glycine max, 185 Medicago truncatula, and 130 Oryza sativa MYB proteins were downloaded from the Plant Transcription Factor Database. These sequences were used as queries in a BLAST search against the M. sativa proteome sequences provided by the Noble Research Institute.

Results

In the present study, a total of 265 MsMYB proteins were obtained, including 50 R1-MYB, 186 R2R3-MYB, 26 R1R2R3-MYB, and three atypical-MYB proteins. These predicted MsMYB proteins were divided into 12 subgroups by phylogenetic analysis, and gene ontology (GO) analysis indicated that most of the MsMYB genes are involved in various biological processes. The expression profiles and quantitative real-time PCR analysis indicated that some MsMYB genes might play a crucial role in the response to abiotic stresses. Additionally, a total of 170 and 914 predicted protein–protein and protein-DNA interactions were obtained, respectively. The interactions between MsMYB043 and MSAD320162, MsMYB253 and MSAD320162, and MsMYB253 and MSAD308489 were confirmed by a yeast two-hybrid system. This work provides information on the MYB family in alfalfa that was previously lacking and might promote the cultivation of stress-resistant alfalfa.

Identification of Genes Differentially Expressed in Response to Cold in Pisum sativum Using RNA Sequencing Analyses

Low temperature stress affects growth and development in pea (Pisum sativum L.) and decreases yield. In this study, RNA sequencing time series analyses performed on lines, Champagne frost-tolerant and Térèse frost-sensitive, during a low temperature treatment versus a control condition, led us to identify 4981 differentially expressed genes. Thanks to our experimental design and statistical analyses, we were able to classify these genes into three sets. The first one was composed of 2487 genes that could be related to the constitutive differences between the two lines and were not regulated during cold treatment. The second gathered 1403 genes that could be related to the chilling response. The third set contained 1091 genes, including genes that could be related to freezing tolerance. The identification of differentially expressed genes related to cold, oxidative stress, and dehydration responses, including some transcription factors and kinases, confirmed the soundness of our analyses. In addition, we identified about one hundred genes, whose expression has not yet been linked to cold stress. Overall, our findings showed that both lines have different characteristics for their cold response (chilling response and/or freezing tolerance), as more than 90% of differentially expressed genes were specific to each of them.

Comparative Transcriptomic and Physiological Analyses of Medicago sativa L. Indicates that Multiple Regulatory Networks Are Activated during Continuous ABA Treatment

Alfalfa is the most extensively cultivated forage legume worldwide. However, the molecular mechanisms underlying alfalfa responses to exogenous abscisic acid (ABA) are still unknown. In this study, the first global transcriptome profiles of alfalfa roots under ABA treatments for 1, 3 and 12 h (three biological replicates for each time point, including the control group) were constructed using a BGISEQ-500 sequencing platform. A total of 50,742 isoforms with a mean length of 2541 bp were generated, and 4944 differentially expressed isoforms (DEIs) were identified after ABA deposition. Metabolic analyses revealed that these DEIs were involved in plant hormone signal transduction, transcriptional regulation, antioxidative defense and pathogen immunity. Notably, several well characterized hormone signaling pathways, for example, the core ABA signaling pathway, was activated, while salicylic acid, jasmonate and ethylene signaling pathways were mainly suppressed by exogenous ABA. Moreover, the physiological work showed that catalase and peroxidase activity and glutathione and proline content were increased after ABA deposition, which is in accordance with the dynamic transcript profiles of the relevant genes in antioxidative defense system. These results indicate that ABA has the potential to improve abiotic stress tolerance, but that it may negatively regulate pathogen resistance in alfalfa.