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Shoot branching is one of the most variable determinants of crop yield, and the signaling pathways of plant branches have become a hot research topic. As an important transcription factor in the B3 family, NGATHA1 (NGA1), plays an important role in regulating plant lateral organ development and hormone synthesis and transport, but few studies of the role of this gene in the regulation of plant growth and stress tolerance have been reported. In this study, the NGA1 gene was isolated from Medicago truncatula (Mt) and its function was characterized. The cis-acting elements upstream of the 5′ end of MtNGA1 and the expression pattern of MtNGA1 were analyzed, and the results indicated that the gene may act as a regulator of stress resistance. A plant expression vector was constructed and transgenic Arabidopsis plants were obtained. Transgenic Arabidopsis showed delayed flowering time and reduced branching phenotypes. Genes involved in the regulation of branching and flowering were differentially expressed in transgenic plants compared with wild-type plants. Furthermore, transgenic plants demonstrated strong tolerances to salt- and mannitol-induced stresses, which may be due to the upregulated expression of NCED3 (NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3) by the MtNGA1 gene. These results provide useful information for the exploration and genetic modification use of MtNGA1 in the future.

Red clover ( L.) is an important cool-season legume plant, which is used as forage. Leaf senescence is a critical developmental process that negatively affects plant quality and yield. The regulatory mechanism of leaf senescence has been studied, and genes involved in leaf senescence have been cloned and characterized in many plants. However, those works mainly focused on model plants. Information about regulatory pathways and the genes involved in leaf senescence in red clover is very sparse. In this study, to better understand leaf senescence in red clover, transcriptome analysis of mature and senescent leaves was investigated using RNA-Seq. A total of about 35,067 genes were identified, and 481 genes were differentially expressed in mature and senescent leaves. Some identified differentially expressed genes showed similar expression patterns as those involved in leaf senescence in other species, such as Arabidopsis, and rice. Differentially expressed genes were confirmed by quantitative real-time PCR (qRT-PCR). Genes involved in signal transduction, transportation and metabolism of plant hormones, transcription factors and plant senescence were upregulated, while the downregulated genes were primarily involved in nutrient cycling, lipid/carbohydrate metabolism, hormone response and other processes. There were 64 differentially expressed transcription factor genes identified by RNA-Seq, including ERF, WRKY, bHLH, MYB and NAC. A total of 90 genes involved in biosynthesis, metabolism and transduction of plant hormones, including abscisic acid, jasmonic acid, cyokinin, brassinosteroid, salicylic acid and ethylene, were identified. Furthermore, 207 genes with direct roles in leaf senescence were demonstrated, such as senescence-associated genes. These genes were associated with senescence in other plants. Transcriptome analysis of mature and senescent leaves in red clover provides a large number of differentially expressed genes. Further analysis and identification of senescence-associated genes can provide new insight into the regulatory mechanisms of leaf development and senescence in legume plant and red clover.

Ryegrass (Lolium perenne L.), a high-quality forage grass, is a good nutrient source for herbivorous livestock. However, improving nitrogen use efficiency and avoiding nitrate toxicity caused by excessive nitrogen are continual challenges in ryegrass production. The molecular mechanism underlying the response of ryegrass to nitrogen, especially excessive nitrogen, remains unclear. In this study, the transcriptomic changes under different nitrogen levels were investigated in perennial ryegrass by high-throughput next-generation RNA sequencing. Phenotypic characterization showed that treatment with half of the standard N concentration (N0.5) led to a better growth state than the other three treatments. The treatments with the standard N concentration (N1) and treatments with ten times higher than the standard N concentration (N10) contained excessive nitrogen, which placed stress on plant growth. Analysis of differentially expressed genes indicated that 345 and 104 genes are involved in the regulation of nitrogen utilization and excessive nitrogen stress, respectively. KEGG enrichment analysis suggested that “photosynthesis-antenna proteins” may respond positively to appropriate nitrogen conditions, whereas “steroid biosynthesis”, “carotenoid biosynthesis” and “C5-branched dibasic acid metabolism” were identified as the top significantly enriched pathways in response to excessive nitrogen. Additionally, 21 transcription factors (TFs) related to nitrogen utilization were classified into 10 families, especially the AP2-EREBP and MYB TF families. Four TFs related to excessive nitrogen stress were identified, including LOBs, NACs, AP2-EREBPs and HBs. The expression patterns of these selected genes were also analyzed. These results provide new insight into the regulatory mechanism of ryegrass in response to nitrogen utilization and excessive nitrogen stress.

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