Complete chloroplast genomes of eight Artemisia species: Comparative analysis, molecular identification, and phylogenetic analysis

Artemisia L. is the largest genus in the Asteraceae, and well known for its high medicinal value. The morphological features of Artemisia species are similar, making taxonomic identification and evolutionary research difficult. We sequenced chloroplast genomes of eight Artemisia species, all of which are common adulterants of A. argyi. We used novel genetic data and compared these data to the published A. argyi chloroplast genome in to develop molecular markers for species identification and reconstructing phylogenetic relationships between Artemisia species. The eight chloroplast sequences were highly similar in gene order, content, and structure, encoding a total of 114 genes (82 protein-coding genes, 28 tRNAs, and four rRNAs). All species harboured similar repeat sequences and simple sequence repeats (SSRs), ranging from 47 to 49 and 38 to 40 repeats, respectively. In addition, we identified five hypervariable regions (rpl32-trnL, rps16-trnQ, petN-psbM, trnE-rpoB, and atpA-trnR) and ten variable coding genes (ycf1, psbG, rpl36, psaC, psaI, accD, psbT, ndhD, ndhE, and psbH), which can be used to develop chloroplast molecular markers. Finally, phylogenetic reconstructions based on six datasets produced similar topologies, revealing A. argyi is closely related to species often found as adulterants, as expected. Our research provides valuable new information on the evolution and phylogenetic relationships between Artemisia chloroplast genomes and identifies valuable molecular makers to distinguish it from closely related species.

Effects of phosphorus stress on the growth and secondary metabolism of Artemisia argyi

Phosphorus is essential in critical plant processes such as signaling, photosynthesis, energy metabolism, and enzyme activity during respiration. Phosphorus stress therefore has a significant impact on plant growth and metabolism. Here, we characterized the biochemical responses of Artemisia argyi Level. et Vant to low phosphorus (LP) and high phosphorus (HP) stress. Plants were treated with 0 g (LP), 1.5 g (control), or 3 g (HP) P per 10 kg of soil. The results demonstrated that CK encouraged the most plant growth, as quantified by leaf size and plant biomass. We also found that the total amounts of phenolic and flavonoid compounds (such as chlorogenic acid, isochlorogenic acid A, isochlorogenic acid B, isochlorogenic acid C, cryptochlorogenic acid, neochlorogenic acid, hispidulin, jaceosidin, eupatilin, and casticin) were increased in the leaves of A. argyi plants exposed to LP stress compared to those raised under CK conditions. The levels of these compounds were inversely related to the amount of phosphorus added, and therefore peaked in plants treated with LP stress. Levels of terpenoids were also found to fluctuate under LP and HP stress compared to CK conditions. Furthermore, transcriptomic analyses showed up-regulation of several genes encoding key enzymes in the flavonoid and phenolic acid metabolic pathways under LP stress. There were also alterations in the expression levels of genes in the methylerythritol 4-phosphate and mevalonate pathways of terpene synthesis. This study contributes to a deeper understanding of the physiological and molecular mechanisms underlying phosphorus stress responses and their impacts on the growth and quality of the economically important species A. argyi.

Mechanisms governing the impact of nitrogen stress on the formation of secondary metabolites in Artemisia argyi leaves

Nitrogen is a key factor in various physiological and metabolic processes in plants. Providing an adequate supply of nitrogen is essential for improving the total yield and quality of the medicinal plant Artemisia argyi (A. argyi), but the underlying mechanisms of how this nutrient alters the crop remains unclear. In this study, we conducted a series of pot experiments to investigate the agronomic traits and active components in the leaves of A. argyi plants under low and high nitrogen stress. Additionally, we used transcriptome analysis and RT-qPCR to explore the molecular pathways associated with nitrogen stress. Our results demonstrate a dramatic increase in the accumulation of phenolic acids and flavonoids in the low nitrogen (LN) stress group compared to the control (CK), with increases of 40.00% and 79.49%, respectively. Interestingly, plants in the high nitrogen (HN) stress group exhibited enhanced plant growth with larger leaves, thicker stems, and a 3% increase in volatile oil content compared to the CK. Moreover, A. argyi in the HN group displayed a 66% increase in volatile oil concentration compared to the LN group. Our combined transcriptome and q-PCR results indicate that LN stress promotes the expression of genes involved in flavonoid synthesis, while HN stress promotes the expression of genes related to terpene skeleton production and photosynthesis. Taken together, these findings suggest that different gene expression levels under LN and HN stress contribute to the photosynthesis capacity and the accumulation of active ingredients in A. argyi leaves. Our results elucidate the physiological and molecular mechanisms of nitrogen stress on A. argyi secondary metabolites and guide fertilization strategies for plant cultivation.