Symbiosis between Dendrobium catenatum protocorms and Serendipita indica involves the plant hypoxia response pathway.

Mycorrhizae are ubiquitous symbioses established between fungi and plant roots. Orchids, in particular, require compatible mycorrhizal fungi for seed germination and protocorm development. Unlike arbuscular mycorrhizal fungi, which have wide host ranges, orchid mycorrhizal fungi are often highly specific to their host orchids. However, the molecular mechanism of orchid mycorrhizal symbiosis is largely unknown compared to that of arbuscular mycorrhizal and rhizobial symbiosis. Here, we report that an endophytic Sebacinales fungus, Serendipita indica, promotes seed germination and the development of protocorms into plantlets in several epiphytic Epidendroideae orchid species (6 species in 2 genera), including Dendrobium catenatum, a critically endangered orchid with high medicinal value. Although plant-pathogen interaction and high meristematic activity can induce the hypoxic response in plants, it has been unclear whether interactions with beneficial fungi, especially mycorrhizal ones, also involve the hypoxic response. By studying the symbiotic relationship between D. catenatum and S. indica, we determined that hypoxia-responsive genes, such as those encoding alcohol dehydrogenase (ADH), are highly induced in symbiotic D. catenatum protocorms. In situ hybridization assay indicated that the ADH gene is predominantly expressed in the basal mycorrhizal region of symbiotic protocorms. Additionally, the ADH inhibitors puerarin and 4-methylpyrazole both decreased S. indica colonization in D. catenatum protocorms. Thus, our study reveals that S. indica is widely compatible with orchids and that ADH and its related hypoxia-responsive pathway are involved in establishing successful symbiotic relationships in germinating orchids.

High Ambient Temperature Regulated the Plant Systemic Response to the Beneficial Endophytic Fungus Serendipita indica.

Most plants in nature establish symbiotic associations with endophytic fungi in soil. Beneficial endophytic fungi induce a systemic response in the aboveground parts of the host plant, thus promoting the growth and fitness of host plants. Meanwhile, temperature elevation from climate change widely affects global plant biodiversity as well as crop quality and yield. Over the past decades, great progresses have been made in the response of plants to high ambient temperature and to symbiosis with endophytic fungi. However, little is known about their synergistic effect on host plants. The endophytic fungus Serendipita indica colonizes the roots of a wide range of plants, including Arabidopsis. Based on the Arabidopsis-S. indica symbiosis experimental system, we analyzed the synergistic effect of high ambient temperature and endophytic fungal symbiosis on host plants. By transcriptome analysis, we found that DNA replication-related genes were significantly upregulated during the systemic response of Arabidopsis aboveground parts to S. indica colonization. Plant hormones, such as jasmonic acid (JA) and ethylene (ET), play important roles in plant growth and systemic responses. We found that high ambient temperature repressed the JA and ET signaling pathways of Arabidopsis aboveground parts during the systemic response to S. indica colonization in roots. Meanwhile, PIF4 is the central hub transcription factor controlling plant thermosensory growth under high ambient temperature in Arabidopsis. PIF4 is also involving JA and/or ET signaling pathway. We found that PIF4 target genes overlapped with many differentially expressed genes (DEGs) during the systemic response, and further showed that the growth promotion efficiency of S. indica on the pif4 mutant was higher than that on the wild-type plants. In short, our data showed that high ambient temperature strengthened the growth promotion effect of S. indica fungi on the aboveground parts of the host plant Arabidopsis, and the growth promotion effect of the systemic response under high ambient temperature was regulated by PIF4.

[VOCs and Odors Control and Development in Pharmaceutical Fermentation Industry].

Volatile organic compounds (VOCs) and odors, which pose potential hazards to human health and the ecosystem, are two of the most important pollutants emitted from the pharmaceutical fermentation industry. Currently, basic research on the characteristics of the pollution and effective prevention technology for VOCs and odors emitted from the pharmaceutical fermentation industry are limited. Specifically, the pharmaceutical fermentation industry lacks adequate theoretical guidance on the supervision and control of VOCs and odors, and some companies even face relocations. Using the pharmaceutical fermentation industry as the study object, the pollution characteristics of VOCs and odors emitted from different production workshops, sewage treatment stations, and the disposal of pharmaceutical residues were assessed. Based on the studies above, the progress of research into representative control technologies were also reviewed systematically. For VOCs and odors control in the pharmaceutical fermentation industry, four suggestions for future research were proposed:① The production processes should be optimized, and the discharge of pollution should be reduced throughout the entire processes; ② Basic research should be carried out on the pollution characteristics of the VOCs and odors emitted from the pharmaceutical fermentation industry, and a rapid and effective method to trace the sources of VOCs and odors should be established; ③ A comprehensive evaluation of control technologies should be conducted, taking cost and efficiency into account; ④ Emission standards and technical orders for VOCs and odors in the pharmaceutical fermentation industry should be formulated and implemented immediately.