Melatonin (N-acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule that plays important roles in plant growth, development and stress responses. Alfalfa (Medicago sativa L.) is an important and widely cultivated leguminous forage crop with high biomass yield and rich nutritional value. The effects of exogenous melatonin content regulation on alfalfa stress tolerance have been investigated in recent years. Here, we isolated and introduced the MsASMT1 (N-acetylserotonin methyltransferase) gene into alfalfa, which significantly improved the endogenous melatonin content. Compared with wildtype (WT) plants, MsASMT1 overexpression (OE-MsASMT1) plants exhibited a series of phenotypic changes, including vigorous growth, increased plant height, enlarged leaves and robust stems with increased cell sizes, cell numbers and vascular bundles, as well as more branches. We also found that the flavonoid content and lignin composition of syringyl to guaiacyl ratio (S/G) were decreased and the cellulose content was increased in OE-MsASMT1 transgenic alfalfa. Further transcriptomic and metabolomic exploration revealed that a large group of genes in phenylalanine pathway related to flavonoids and lignin biosynthesis were significantly altered, accompanied by significantly reduced concentrations of the glycosides of quercetin, kaempferol, formononetin and biochanin in OE-MsASMT1 transgenic alfalfa. Our study first uncovers the effects of endogenous melatonin on alfalfa growth and metabolism. This report provides insights into the regulation effects of melatonin on plant growth and phenylalanine metabolism, especially flavonoids and lignin biosynthesis.
Waxy cuticle plays an important role in the resistance to various biotic and abiotic stresses. Barley is generally covered with cuticular wax, but glossy mutants are shiny green without wax. The morphological structure of wax was found to be significantly different between the glossy mutant and the wild-type line when examined under a scanning electron microscope. Transcriptomic analysis was performed to identify genes related to waxy cuticle formation. A total of 243 differentially expressed genes (DEGs) were detected. Seven unigenes related to waxy cuticle biosynthesis were confirmed by quantitative realtime PCR. Results were highly consistent with the RNA-Seq results. Differential expressions of WAX2, WSD1, FAR1, and LACS could potentially explain the differences in the cuticular waxes of the two barley lines. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway-enrichment analyses were performed to better understand the functions of these DEGs. This study not only provides valuable information for understanding the molecular mechanisms of the synthesis of cuticular waxes and metabolism, but also establishes the foundations for further genomics research and waxy gene cloning in barley.
Cadmium (Cd) in soil inhibits plant growth and development and even harms human health through food chain transmission. Switchgrass (Panicum virgatum L.), a perennial C4 biofuel crop, is considered an ideal plant for phytoremediation due to its high efficiency in removing Cd and other heavy metals from contaminated soil. The key to understanding the mechanisms of switchgrass Cd tolerance is to identify the genes involved in Cd transport. Heavy-metal ATPases (HMAs) play pivotal roles in heavy metal transport, including Cd, in Arabidopsis thaliana and Oryza sativa, but little is known about the functions of their orthologs in switchgrass. Therefore, we identified 22 HMAs in switchgrass, which were distributed on 12 chromosomes and divided into 4 groups using a phylogenetic analysis. Then, we focused on PvHMA2.1, which is one of the orthologs of the rice Cd transporter OsHMA2. We found that PvHMA2.1 was widely expressed in roots, internodes, leaves, spikelets, and inflorescences, and was significantly induced in the shoots of switchgrass under Cd treatment. Moreover, PvHMA2.1 was found to have seven transmembrane domains and localized at the cell plasma membrane, indicating that it is a potential transporter. The ectopic expression of PvHMA2.1 alleviated the reduction in primary root length and the loss of fresh weight of Arabidopsis seedlings under Cd treatment, suggesting that PvHMA2.1 enhanced Cd tolerance in Arabidopsis. The higher levels of relative water content and chlorophyll content of the transgenic lines under Cd treatment reflected that PvHMA2.1 maintained water retention capacity and alleviated photosynthesis inhibition under Cd stress in Arabidopsis. The roots of the PvHMA2.1 ectopically expressed lines accumulated less Cd compared to the WT, while no significant differences were found in the Cd contents of the shoots between the transgenic lines and the WT under Cd treatment, suggesting that PvHMA2.1 reduced Cd absorption from the environment through the roots in Arabidopsis. Taken together, our results showed that PvHMA2.1 enhanced Cd tolerance in Arabidopsis, providing a promising target that could be engineered in switchgrass to repair Cd-contaminated soil.
Starch content is an important trait in barley. To evaluate the genetic diversity and identify molecular markers of starch content in barley, 40 cultivated barley genotypes collected from different regions, including genotypes whose starch content is at either the high or low end of the spectrum (15), were used in this study. All the genotypes were re-sequenced by the double-digest-restriction associated DNA sequencing method, and a total of 299,103 single-nucleotide polymorphism (SNP) markers were obtained. The genotypes were divided into four sub-populations based on FASTSTRUCTURE, principal component analysis and neighbour-joining tree analysis. All four sub-populations had a high linkage disequilibrium, especially group 3, whose members were recently bred for malting in the Jiangsu coastal area. The starch content of the barley lines was evaluated during three growing seasons (2014–2017), and the average values of starch content across the three growing seasons at the low and high ends were 51.5 and 55.0%, respectively. The starch content was affected by population structure, the barley in group 2 had a low starch content, while the barley in group 4 had a high starch content. Twenty-six SNP markers were identified as being significantly associated with starch content (P ⩽ 0.001) based on the average values across the three growing seasons using the mixed linear model method. These SNP markers were located on chromosomes 1H and 4H, and were considered loci of qSC1-1 and qSC4-1, respectively. The major identified QTLs for starch content are helpful for further research on carbohydrates and for barley breeding.
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