Annual ryegrass (Lolium multiflorum L.) is a commercially important, widely distributed forage crop that is used in the production of hay and silage worldwide. Drought has been a severe environmental constraint in its production. Nevertheless, only a handful of studies have examined the impact of short-term drought stress on annual ryegrass. The aim of this study was to explore how stress-induced core metabolic processes enhance drought tolerance, or adaptation to drought, in annual ryegrass. We profiled the transcriptomes, proteomes, and metabolomes of two annual ryegrass genotypes: the drought-resistant genotype “Abundant 10” and drought-susceptible genotype “Adrenalin 11.” We identified differentially expressed metabolites and their corresponding proteins and transcripts that are involved in 23 core metabolic processes, in response to short-term drought stress. Protein–gene–metabolite correlation networks were built to reveal the relationships between the expression of transcripts, proteins, and metabolites in drought-resistant annual ryegrass. Furthermore, integrated metabolic pathways were used to observe changes in enzymes corresponding with levels of amino acids, lipids, carbohydrate conjugates, nucleosides, alkaloids and their derivatives, and pyridines and their derivatives. The resulting omics data underscored the significance of 23 core metabolic processes on the enhancement of drought tolerance or adaptation to drought in annual ryegrass. The regulatory networks were inferred using MCoA and correlation analysis to reveal the relationships among the expression of transcripts, proteins, and metabolites that highlight the corresponding elements of these core metabolic pathways. Our results provide valuable insight into the molecular mechanisms of drought resistance, and represent a promising strategy toward the improvement of drought tolerance in annual ryegrass.

King grass, a hybrid grass between pearl millet and elephant grass, has many excellent characteristics such as high biomass yield, great stress tolerance, and enormous economic and ecological value, which makes it ideal for development of phytoremediation. At present, the physiological and molecular response of king grass to cadmium (Cd) stress is poorly understood. Transcriptome analysis of early response (3 h and 24 h) of king grass leaves and roots to high level Cd (100 µM) has been investigated and has shed light on the molecular mechanism underlying Cd stress response in this hybrid grass. Our comparative transcriptome analysis demonstrated that in combat with Cd stress, king grass roots have activated the glutathione metabolism pathway by up-regulating glutathione S-transferases (GSTs) which are a multifunctional family of phase II enzymes that detoxify a variety of environmental chemicals, reactive intermediates, and secondary products of oxidative damages. In roots, early inductions of phenylpropanoid biosynthesis and phenylalanine metabolism pathways were observed to be enriched in differentially expressed genes (DEGs). Meanwhile, oxidoreductase activities were significantly enriched in the first 3 h to bestow the plant cells with resistance to oxidative stress. We also found that transporter activities and jasmonic acid (JA)-signaling might be activated by Cd in king grass. Our study provided the first-hand information on genome-wide transcriptome profiling of king grass and novel insights on phytoremediation.

Vernalization and the transition from vegetative to reproductive growth involve multiple pathways, vital for controlling floral organ formation and flowering time. However, little transcription information is available about the mechanisms behind environmental adaption and growth regulation. Here, we used high-throughput sequencing to analyze the comprehensive transcriptome of Dactylis glomerata L. during six different growth periods. During vernalization, 4689 differentially expressed genes (DEGs) significantly increased in abundance, while 3841 decreased. Furthermore, 12,967 DEGs were identified during booting stage and flowering stage, including 7750 up-regulated and 5219 down-regulated DEGs. Pathway analysis indicated that transcripts related to circadian rhythm, photoperiod, photosynthesis, flavonoid biosynthesis, starch, and sucrose metabolism changed significantly at different stages. Coexpression and weighted correlation network analysis (WGCNA) analysis linked different stages to transcriptional changes and provided evidence of inner relation modules associated with signal transduction, stress responses, cell division, and hormonal transport. We found enrichment in transcription factors (TFs) related to WRKY, NAC, AP2/EREBP, AUX/IAA, MADS-BOX, ABI3/VP1, bHLH, and the CCAAT family during vernalization and floral bud development. TFs expression patterns revealed intricate temporal variations, suggesting relatively separate regulatory programs of TF modules. Further study will unlock insights into the ability of the circadian rhythm and photoperiod to regulate vernalization and flowering time in perennial grass.

Water deficit adversely affects the growth and productivity of annual ryegrass (Lolium multiflorum Lam.). The exogenous application of chitosan (CTS) has gained extensive interests due to its effect on improving drought resistance. This research aimed to determine the role of exogenous CTS on annual ryegrass in response to water stress. Here, we investigated the impact of exogenous CTS on the physiological responses and transcriptome changes of annual ryegrass variety “Tetragold” under osmotic stress induced by exposing them to 20% polyethylene glycol (PEG)-6000. Our experimental results demonstrated that 50 mg/L exogenous CTS had the optimal effect on promoting seed germination under osmotic stress. Pre-treatment of annual ryegrass seedlings with 500 mg/L CTS solution reduced the level of electrolyte leakage (EL) as well as the contents of malondialdehyde (MDA) and proline and enhanced the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbic acid peroxidase (APX) under osmotic stress. In addition, CTS increased soluble sugars and chlorophyll (Chl) content, net photosynthetic rate (A), stomatal conductance (gs), water use efficiency (WUE), and transpiration rate (E) in annual ryegrass seedlings in response to three and six days of osmotic stress. Transcriptome analysis further provided a comprehensive understanding of underlying molecular mechanisms of CTS impact. To be more specific, in contrast of non-treated seedlings, the distinct changes of gene expressions of CTS-treated seedlings were shown to be tightly related to carbon metabolism, photosynthesis, and plant hormone. Altogether, exogenous CTS could elicit drought-related genes in annual ryegrass, leading to resistance to osmotic stress via producing antioxidant enzymes and maintaining intact cell membranes and photosynthetic rates. This robust evidence supports the potential of the application of exogenous CTS, which will be helpful for determining the suitability and productivity of agricultural crops.

In mammals, formation of the auditory sensory organ (the organ of Corti) is restricted to a specialized area of the cochlea. However, the molecular mechanisms limiting sensory formation to this discrete region in the ventral cochlear duct are not well understood, nor is it known whether other regions of the cochlea have the competence to form the organ of Corti. Here we identify LMO4, a LIM-domain-only nuclear protein, as a negative regulator of sensory organ formation in the cochlea. Inactivation of Lmo4 in mice leads to an ectopic organ of Corti (eOC) located in the lateral cochlea. The eOC retains the features of the native organ, including inner and outer hair cells, supporting cells, and other nonsensory specialized cell types. However, the eOC shows an orientation opposite to the native organ, such that the eOC appears as a mirror-image duplication to the native organ of Corti. These data demonstrate a novel sensory competent region in the lateral cochlear duct that is regulated by LMO4 and may be amenable to therapeutic manipulation.

Amino acid metabolism constitutes a major metabolic pathway in plants, playing an important role in the modulation of plant responses to stress. In this study, we investigated the amino acid metabolism responses of M. sativa (Medicago sativa L.) and M. truncatula (Medicago truncatula L.) plants under salt stress using transcriptomic and proteomic approaches to elucidate their salt stress tolerance mechanisms in relation to the regulation of amino acid homeostasis. Transcriptome and proteome sequencing followed by Kyoto Gene and Genome Encyclopedia enrichment analysis revealed 34 differentially expressed genes and 45 differentially expressed proteins involved in valine, leucine, and isoleucine degradation, tyrosine metabolism, and glutathione metabolism. Significant differences were observed in the expression of glutathione S-transferase (GST) within the glutathione metabolic pathway between M. sativa and M. truncatula. The induction of valine, leucine, and isoleucine metabolism, aldehyde dehydrogenases (ALDHs), and alanine-glyoxylate aminotransferases (AGXTs), involved in intracellular reactive oxygen species scavenging, also significantly differed under salt stress. Significant differences were identified in the expression of tyrosine decarboxylases (TDCs) involved in tyrosine metabolism, which are responsible for tyramine biosynthesis and can enhance plant tolerance to salt stress. This study delved into the effects of amino acid metabolism on the salt tolerance mechanisms of M. sativa and M. truncatula, which is crucial in guiding the future breeding of salt-tolerant alfalfa varieties.