Salt stress is among the most severe abiotic stresses in plants worldwide. Medicago truncatula is a model plant for legumes and analysis of its response to salt stress is helpful for providing valuable insights into breeding. However, few studies have focused on illustrating the whole-transcriptome molecular mechanism underlying salt stress response in Medicago truncatula. Herein, we sampled the leaves of Medicago truncatula treated with water or NaCl and analyzed the characteristics of its coding and non-coding RNAs. We identified a total of 4,693 differentially expressed mRNAs (DEmRNAs), 505 DElncRNAs, 21 DEcircRNAs, and 55 DEmiRNAs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed that their functions were mostly associated with metabolic processes. We classified the lncRNAs and circRNAs into different types and analyzed their genomic distributions. Furthermore, we predicted the interactions between different RNAs based on the competing endogenous RNA (ceRNA) theory and identified multiple correlation networks, including 27 DEmiRNAs, 43 DEmRNAs, 19 lncRNAs, and 5 DEcircRNAs. In addition, we comprehensively analyzed the candidate DEmRNAs and ceRNAs and found that they were involved in Ca+ signaling, starch and sucrose biosynthesis, phenylpropanoid and lignin metabolism, auxin and jasmonate biosynthesis, and transduction pathways. Our integrated analyses in salt stress response in Medicago truncatula revealed multiple differentially expressed coding and non-coding RNAs, including mRNAs, lncRNAs, circRNAs, and miRNAs, and identified multiple DEmRNA and ceRNA interaction pairs that function in many pathways, providing insights into salt stress response in leguminous plants.

Gibberellins (GA) are important hormones in the regulation of plant growth and development, especially plant dwarfism. In the present study, the leaf length and active gibberellin content of a dwarf mutant were lower than that of Kentucky bluegrass (Poa pratensis L.) wild type, and the plant height of the dwarf mutant increased following the application of GA3. To gain insights into the GA metabolism pathway in turfgrass and the role of GA‐related genes in the dwarf phenotype, five GA‐related genes in P. pratensis, namely PpKS, PpKO, PpGA20ox1, PpGA3ox1, and PpGA2ox5, were isolated and identified. According to expression analysis, the expression levels of PpKS were lower in the dwarf mutant than in the wild type, whereas the transcript abundances of PpGA20ox1 and PpGA2ox5 were raised in dwarf mutant. Further evaluation of the expression profiles of these genes in response to GA3 showed that the studied genes were differentially regulated after exogenous treatment. Furthermore, it was found that PpGA2ox5‐overexpressing transgenic lines produced the phenotypes of dwarfism and dark green blades, whereas PpGA20ox1 overexpression in Arabidopsis had the opposite effect. Through the result of the diverse expression patterns of GA genes and functional study of PpGA2ox5 and PpGA20ox1, it is indicated that the genes involved in the metabolism of GA are important for regulating plant height and speculated that PpGA2ox5 could be the breeding target that used to cultivate dwarf varieties of Kentucky bluegrass.

In plant cells, the nucleus DNA is considered the primary site of injury by the space environment, which could generate genetic alteration. As the part of genomic mutation, genetic variation in the promoter region could regulate gene expression. In the study, it is observed that there is a deletion in the upstream regulatory region of the 1-deoxy-d-xylulose-5-phosphate synthase 1 gene (PpDXS1) of Poa pratensis dwarf mutant and the PpDXS1 transcript abundance is lower in the dwarf mutant. It is indicated that the deletion in the promoter region between wild type and dwarf mutant could be responsible for the regulation of PpDXS1 gene expression. The PpDXS1 promoter of dwarf mutant shows a lower activity as determined by dual luciferase assay in Poa pratensis protoplast, as well as the GUS activity is lower in transgenic Poa pratensis plant. To further investigate the effect of the deletion in the promoter region on PpDXS1 transcript accumulation, the transient assay and yeast one-hybrid experiment demonstrate that the deletion comprises a motif which is a target of G-box binding factor (GBF1), and the motif correlates with an increase in transactivation by GBF1 protein. Taken together, these results indicate that the deletion in the promoter of PpDXS1 isolated from dwarf mutant is sufficient to account for the decrease in PpDXS1 transcript level and GBF1 can regulate the PpDXS1 gene expression, and subsequently affect accumulation of various isoprenoids throughout the plant.