Shiqing Li

Orchid seed germination requires symbiotic association with mycorrhizal fungi that provide essential nutrients for germination and subsequent growth. Extensive research has elucidated the pivotal role of the mycorrhizal fungus Tulasnella sp. in the modulation of seed germination and growth processes in Bletilla striata (Thunb.) Reiehb.f. However, the molecular mechanisms underlying this symbiosis remain poorly characterized. Our integrated transcriptomic-metabolomic analysis of symbiotic germination revealed that co-cultivation of Tulasnella sp. bj1 with B. striata seeds significantly downregulates the expression of plant-derived flavonoid biosynthetic genes, with flavonoid degradation potentially alleviating germination and growth inhibition. The bj1 strain modulates indoleacetic acid (IAA) biosynthesis in B. striata by upregulating the expression of plant-derived tryptophan decarboxylase (TDC) in the tryptophan pathway and hydrolytic enzymes (NtAMI) in the indoleacetamide pathway, with elevated IAA potentially contributing to seed germination and growth. Moreover, bj1 suppresses the jasmonic acid (JA) biosynthetic pathway of B. striata by downregulating key plant-derived biosynthetic genes, concurrently promoting the accumulation of 12-hydroxyjasmonic acid—a metabolite associated with plant immune regulation that may favor colonization and symbiotic establishment with B. striata seeds. Additionally, bj1 induces the expression of polysaccharide-degrading enzymes, potentially improving carbon source utilization to support protocorm development. In conclusion, bj1 modulates the immune response of B. striata seeds, facilitating the establishment of a symbiotic relationship. Subsequently, the germination and growth of B. striata seeds are enhanced through reduced flavonoid accumulation, increased IAA synthesis, and improved carbon source utilization. Consequently, this investigation provides a crucial foundation for elucidating mechanisms governing symbiotic germination in B. striata.

Plagiomnium acutum T. Kop. (P. acutum) has been used as a traditional Chinese medicine for thousands of years to treat cancer but lacks evidence. The objective of this work was to reveal the chemical composition of P. acutum essential oil (PEO) and explore its potential antitumor activity and molecular mechanism. PEO was prepared by the simultaneous distillation–extraction method and characterized by gas chromatography/mass spectroscopy. CCK8 assay, flow cytometry, western blot, and immunofluorescence techniques were used to analyze the effects and mechanism of PEO against cancer cells. A total of 74 constituents of PEO were identified, with diterpenes (26.5%), sesquiterpenes (23.89%), and alcohols (21.81%) being the major constituents. Two terpenoids, selina-6-en-4-ol and dolabella-3,7-dien-18-ol, were detected in PEO for the first time. PEO showed significant cell growth inhibitory activity on HepG2 and A549 cells by blocking the G1 phase and inducing apoptosis, which may be attributed to its upregulation of p21^Cip1 and p27^Kip1 proteins and interference with mitochondrial membrane potential effect. Dolabella-3,7-dien-18-ol accounts for 25.5% of PEO and is one of the main active components of PEO, with IC₅₀ values in HepG2 and A549 cells of (25.820 ± 0.216) µg/mL and (23.597 ± 1.207) μg/mL, respectively. These results confirmed the antitumor medicinal value of P. acutum and showed great application potential in the pharmaceutical industry.