Genome-wide identification of HMT gene family explores BpHMT2 enhancing selenium accumulation and tolerance in Broussonetia papyrifera.

Broussonetia papyrifera, a valuable feed resource, is known for its fast growth, wide adaptability, high protein content and strong selenium enrichment capacity. Selenomethionine (SeMet), the main selenium form in selenium fortification B. papyrifera, is safe for animals and this enhances its nutritional value as a feed resource. However, the molecular mechanisms underlying SeMet synthesis remain unclear. This study identified three homocysteine S-methyltransferase genes from the B. papyrifera genome. The phylogenetic tree demonstrated that BpHMTs were divided into two classes, and BpHMT2 in the Class 2-D subfamily evolved earlier and possesses more fundamental functions. On the basis of the correlation between gene expression levels and selenium content, BpHMT2 was identified as a key candidate gene associated with selenium tolerance. Subcellular localization experiments confirmed the targeting of BpHMT2 in nucleus, cell membrane and chloroplasts. Moreover, three BpHMT2 overexpression Arabidopsis thaliana lines were confirmed to enhance plant selenium tolerance and SeMet accumulation. Overall, our finding provides insights into the molecular mechanisms of selenium metabolism in B. papyrifera, highlighting the potential role of BpHMT2 in SeMet synthesis. This research contributes to our understanding of selenium-enriched feed resources, with increased SeMet content contributing to the improved nutritional value of B. papyrifera as a feed resource.

Advances in Research on the Involvement of Selenium in Regulating Plant Ecosystems.

Selenium is an essential trace element which plays an important role in human immune regulation and disease prevention. Plants absorb inorganic selenium (selenite or selenate) from the soil and convert it into various organic selenides (such as seleno amino acids, selenoproteins, and volatile selenides) via the sulfur metabolic pathway. These organic selenides are important sources of dietary selenium supplementation for humans. Organoselenides can promote plant growth, improve nutritional quality, and play an important regulatory function in plant ecosystems. The release of selenium-containing compounds into the soil by Se hyperaccumulators can promote the growth of Se accumulators but inhibit the growth and distribution of non-Se accumulators. Volatile selenides with specific odors have a deterrent effect on herbivores, reducing their feeding on plants. Soil microorganisms can effectively promote the uptake and transformation of selenium in plants, and organic selenides in plants can improve the tolerance of plants to pathogenic bacteria. Although selenium is not an essential trace element for plants, the right amount of selenium has important physiological and ecological benefits for them. This review summarizes recent research related to the functions of selenium in plant ecosystems to provide a deeper understanding of the significance of this element in plant physiology and ecosystems and to serve as a theoretical basis and technical support for the full exploitation and rational application of the ecological functions of selenium-accumulating plants.

Comparative physiological and transcriptome analysis reveals the potential mechanism of selenium accumulation and tolerance to selenate toxicity of Broussonetia papyrifera.

Broussonetia papyrifera is an important fodder tree that is widely distributed in China. Enhancing the selenium (Se) content in B. papyrifera may help to improve the nutritional value of the feed. In this study, sodium selenite and selenate were foliar applied to investigate the mechanisms of Se tolerance and accumulation in B. papyrifera. The results showed that both Se forms significantly increased the total Se content, and the proportion of organic Se was significantly higher in the sodium selenite treatment than in the control. In addition, the soluble sugar, phenolic acid and flavonoid contents and antioxidant enzyme activities were increased by exogenous Se. The de novo RNA sequencing results showed that 644 and 1804 differentially expressed genes were identified in the selenite and selenate comparison groups, respectively. Pathway enrichment analysis demonstrated that 24 of the 108 pathways were significantly enriched, of which sulfur assimilation genes in the sodium selenite-treated groups were upregulated, whereas Se conjugation and transporter genes, such as SBP1, PCS, GSTs, ABCs and GPX, were significantly induced under selenate treatment. The hub genes identified by weighted-gene co-expression network analysis further confirmed that sulfur assimilation, conjugation and transporter genes might play a vital role in Se assimilation and tolerance. From this, a model of Se metabolism in B. papyrifera was proposed based on the above physiological and RNA sequencing data. This study is the first study to report that B. papyrifera has a strong ability to accumulate and tolerate exogenous Se, thereby providing a foundation for further characterization of the accumulation and tolerance mechanism of B. papyrifera. Our findings can provide technical support for producing Se-enriched fodder.

Cloning, Expression Profiling and Functional Analysis of CnHMGS, a Gene Encoding 3-hydroxy-3-Methylglutaryl Coenzyme A Synthase from Chamaemelum nobile.

Roman chamomile (Chamaemelum nobile L.) is renowned for its production of essential oils, which major components are sesquiterpenoids. As the important enzyme in the sesquiterpenoid biosynthesis pathway, 3-hydroxy-3-methylglutaryl coenzyme A synthase (HMGS) catalyze the crucial step in the mevalonate pathway in plants. To isolate and identify the functional genes involved in the sesquiterpene biosynthesis of C. nobile L., a HMGS gene designated as CnHMGS (GenBank Accession No. KU529969) was cloned from C. nobile. The cDNA sequence of CnHMGS contained a 1377 bp open reading frame encoding a 458-amino-acid protein. The sequence of the CnHMGS protein was highly homologous to those of HMGS proteins from other plant species. Phylogenetic tree analysis revealed that CnHMGS clustered with the HMGS of Asteraceae in the dicotyledon clade. Further functional complementation of CnHMGS in the mutant yeast strain YSC6274 lacking HMGS activity demonstrated that the cloned CnHMGS cDNA encodes a functional HMGS. Transcript profile analysis indicated that CnHMGS was preferentially expressed in flowers and roots of C. nobile. The expression of CnHMGS could be upregulated by exogenous elicitors, including methyl jasmonate and salicylic acid, suggesting that CnHMGS was elicitor-responsive. The characterization and expression analysis of CnHMGS is helpful to understand the biosynthesis of sesquiterpenoid in C. nobile at the molecular level and also provides molecular wealth for the biotechnological improvement of this important medicinal plant.