Plants in their natural environment frequently face various abiotic stresses, such as drought, high salinity, and chilling. Plant mitochondria contain an alternative oxidase (AOX), which is encoded by a small family of nuclear genes. AOX genes have been shown to be highly responsive to abiotic stresses. Using transgenic plants with varying levels of AOX expression, it has been confirmed that AOX genes are important for abiotic stress tolerance. Although the roles of AOX under abiotic stresses have been extensively studied and there are several excellent reviews on this topic, the differential expression patterns of the AOX gene family members and the signal regulation of AOX gene(s) under abiotic stresses have not been extensively summarized. Here, we review and discuss the current progress of these two important issues.

Trichoderma spp., which widely exist in nature, are always used as plant growth-promoting stimulants. However, there is little reporting about the combined use of Trichoderma strains to promote growth of plants. We explored two different Trichoderma strains (Trichoderma atroviride LX-7 and Trichoderma citrinoviride HT-1) and a mixture of the two on the growth-promoting effects of pakchoi. In this study, in vitro-promoting traits of two Trichoderma strains were determined, and six treatments were used: T. atroviride LX-7, T. citrinoviride HT-1, different mixtures of these two (1:1, 1:2 and 2:1) and no inoculation in the seed germination and pot experiment. The results showed that T.atroviride LX-7 and T. citrinoviride HT-1 had the ability of siderophore and indol acetic acid (IAA) production, and LX-7 had the capacity for potassium solubilization. The highest seed germination percentage (GP), germination energy (GE), germination index (GI), vitality index (VI) and growth of radicles and plumules was observed in the LX-7 + HT-1 (1:1) combination, the highest biomass and quality of plants was observed in the LX-7 + HT-1 (1:2) inoculation (followed by a single LX-7 or HT-1 strain inoculation), while the lowest values were obtained in the untreated seeds or plants. On the basis of this study, combined use of two Trichoderma strains had greater benefits for growth and quality of pakchoi, making this formulation attractive for future field applications.

Investigations of the differences in the metabolites of medicinal plants have typically focused on the effects of external environmental factors. However, little is known about the relationship between endophytes diversity and host metabolites. We used high-throughput sequencing methods to compare the endophyte diversity of Rheum palmatum from eight different production areas in Gansu Province of China and to analyze the association between those areas and five secondary metabolites (aloe-emodin, rhein, emodin, chrysophanol, and physcion). The results show that the diversity and OTUs (Operational taxonomic units) abundance of endophytic fungi and bacteria of R. palmatum differed according to production area. Spearman analysis showed that the five secondary metabolites of R. palmatum were positively correlated with the diversity and abundance of endophytic fungi. Comparing both space and environmental differences to determine influences on community structure, VPA analysis revealed that geographic factors explained more difference in community composition of fungal and bacterial endophytes than climate factors. PICRUSt and FUNGuild predictive analysis indicated that metabolites were the primary components of endophytic bacteria in all samples, while the function of endophytic fungi was composed of dominant trophic modes (saprotroph and pathotroph), and relative abundances were different. Our results help elucidate the correlation of plant–microbe interactions and offer pivotal information to reveal the role of endophytes in the production of R. palmatum and its important secondary metabolite.

Isorhamnetin (ISO), a naturally occurring plant flavonoid, is widely used as a phytomedicine. The major treatment modality for non-small-cell lung carcinoma (NSCLC) is radiotherapy. However, radiotherapy can induce radioresistance in cancer cells, thereby resulting in a poor response rate. Our results demonstrated that pretreatment with ISO induced radiosensitizing effect in A549 cells using colony formation, micronucleus, and γH2AX foci assays. In addition, ISO pretreatment significantly enhanced the radiation-induced incidence of apoptosis, the collapse of mitochondrial membrane potential, and the expressions of proteins associated with cellular apoptosis and suppressed the upregulation of NF-κBp65 induced by irradiation in A549 cells. Interestingly, the expression of interleukin-13 (IL-13), an anti-inflammatory cytokine, was positively correlated with the ISO-mediated radiosensitization of A549 cells. The knockdown of IL-13 expression by RNA interference decreased the IL-13 level and thus reduced ISO-mediated radiosensitivity in cells. We also found that the IR-induced NF-κB signaling activation was inhibited by ISO pretreatment, and it was abrogated in IL-13 silenced cells. We speculated that ISO may confer radiosensitivity on A549 cells via increasing the expression of IL-13 and inhibiting the activation of NF-κB. To our knowledge, this is the first report demonstrating the effects of ISO treatment on the responsiveness of lung cancer cells to irradiation through IL-13 and the NF-κB signaling pathway. In summary, ISO is a naturally occurring radiosensitizer with a potential application in adjuvant radiotherapy.

Derivates of natural products have been wildly utilized in the treatment of malignant tumors. Isorhamnetin (ISO), a most important active ingredient derived from flavonoids, shows great potential in tumor therapy. However, the therapeutic effects of ISO on gastric cancer (GC) remain unclear. Here, we demonstrate that ISO treatment dramatically inhibited the proliferation of two types of GC cells (AGS-1 and HGC-27) both in vitro and in vivo in time- and dose-dependent manners. These results are consistent with the transcriptomic analysis of ISO-treated GC cells, which yielded hundreds of differentially expressed genes that were enriched with cell growth and apoptosis. Mechanically, ISO treatment initiated the activation of caspase-3 cascade and elevated the expression of mitochondria-associated Bax/Bcl-2, cytosolic cytochrome c, followed by the activation of the cleavage of caspase-3 as well as poly ADP-ribose polymerase (PARP), resulting in the severe reduction of the mitochondrial potential and the accumulation of reactive oxygen species (ROS), while pre-treatment of the caspase-3 inhibitor could block the anti-tumor effect. Therefore, these results indicate that ISO treatment induces the apoptosis of GC cells through the mitochondria-dependent apoptotic pathway, providing a potential strategy for clinical GC therapy.

Background: The influence of external environmental factors on secondary metabolites of medicinal plants has always been studied. However, little is known about the relationships between endophytes and host metabolites, especially the relationship differences between different plant species. Thus, we used high-throughput sequencing methods to compare endophyte diversity from roots of two closely related species, Gentiana officinalis and G. siphonantha, from the same production area, and analyze the association with four secondary metabolites (Gentiopicroside, Loganic acid, Swertiamarine and Sweroside). Results: The fungal and bacteria communities’ richness and diversity of G. siphonantha was higher than G. officinalis. Ascomycota and Proteobacteria were dominant fungal and bacterial phylum of the two closely related species. At the genus level, Tetracladium and Cadophora were dominant fungal genus in G. officinalis and G. siphonantha samples, respectively. While Pseudomonas was dominant bacterial genus in two closely related species, with relative abundances were 8.29 and 8.05%, respectively. Spearman analysis showed that the content of loganic acid was significantly positively correlated with endophytic fungi, the content of gentiopicroside, swertiamarine and sweroside were significantly positively correlated with endophytic bacteria in the two related species. PICRUSt and FUNGuild predictive analysis indicated that metabolism and saprotroph was primary function of endophytic bacteria and fungi in the two related species. Conclusion: Our results will expand the knowledge on relationships of plant-microbe interactions and offer pivotal information to reveal the role of endophytes in the production of Gentiana plant and its important secondary metabolite.