Species Diversity and Ecological Habitat of Absidia (Cunninghamellaceae, Mucorales) with Emphasis on Five New Species from Forest and Grassland Soil in China.

Although species of Absidia are known to be ubiquitous in soil, animal dung, and insect and plant debris, the species diversity of the genus and their ecological habitats have not been sufficiently investigated. In this study, we describe five new species of Absidia from forest and grassland soils in southwestern China, with support provided by phylogenetic, morphological, and physiological evidence. The species diversity and ecological habitat of Absidia are summarized. Currently, 22 species are recorded in China, which mainly occur in soil, especially in tropical and subtropical forests and mountains. An updated key to the species of Absidia in China is also provided herein. This is the first overview of the Absidia ecological habitat.

Taxonomy and Phylogeny of Four New Species in Absidia (Cunninghamellaceae, Mucorales) From China.

Four new species within the genus Absidia, A. globospora, A. medulla, A. turgida, and A. zonata, are proposed based on a combination of morphological traits, physiological features, and molecular evidences. A. globospora is characterized by globose sporangiospores, a 1.0- to 3.5-µm-long papillary projection on columellae, and sympodial sporangiophores. A. medulla is characterized by cylindrical to oval sporangiospores, a 1.0- to 4.5-µm-long bacilliform projection on columellae, and spine-like rhizoids. A. turgida is characterized by variable sporangiospores, up to 9.5-µm-long clavate projections on columellae, and swollen top of the projection and inflated hyphae. A. zonata is characterized by cylindrical to oval sporangiospores, a 2.0- to 3.5-µm-long spinous projection on columellae, and as many as eight whorled sporangiophores. Phylogenetic analyses based on sequences of internal transcribed spacer rDNA and D1-D2 domains of LSU rDNA support the novelty of these four species within the Absidia. All new species are illustrated, and an identification key to all the known species of Absidia in China is included.

Transcriptome Reveals Roles of Lignin-Modifying Enzymes and Abscisic Acid in the Symbiosis of Mycena and Gastrodia elata.

Gastrodia elata is a well-known medicinal and heterotrophic orchid. Its germination, limited by the impermeability of seed coat lignin and inhibition by abscisic acid (ABA), is triggered by symbiosis with fungi such as Mycena spp. However, the molecular mechanisms of lignin degradation by Mycena and ABA biosynthesis and signaling in G. elata remain unclear. In order to gain insights into these two processes, this study analyzed the transcriptomes of these organisms during their dynamic symbiosis. Among the 25 lignin-modifying enzyme genes in Mycena, two ligninolytic class II peroxidases and two laccases were significantly upregulated, most likely enabling Mycena hyphae to break through the lignin seed coats of G. elata. Genes related to reduced virulence and loss of pathogenicity in Mycena accounted for more than half of annotated genes, presumably contributing to symbiosis. After coculture, upregulated genes outnumbered downregulated genes in G. elata seeds, suggesting slightly increased biological activity, while Mycena hyphae had fewer upregulated than downregulated genes, indicating decreased biological activity. ABA biosynthesis in G. elata was reduced by the downregulated expression of 9-cis-epoxycarotenoid dioxygenase (NCED-2), and ABA signaling was blocked by the downregulated expression of a receptor protein (PYL12-like). This is the first report to describe the role of NCED-2 and PYL12-like in breaking G. elata seed dormancy by reducing the synthesis and blocking the signaling of the germination inhibitor ABA. This study provides a theoretical basis for screening germination fungi to identify effective symbionts and for reducing ABA inhibition of G. elata seed germination.

Two New Species in the Family Cunninghamellaceae from China.

The species within the family Cunninghamellaceae are widely distributed and produce important metabolites. Morphological studies along with a molecular phylogeny based on the internal transcribed spacer (ITS) and large subunit (LSU) of ribosomal DNA revealed two new species in this family from soils in China, that is, Absidia ovalispora sp. nov. and Cunninghamella globospora sp. nov. The former is phylogenetically closely related to Absidia koreana, but morphologically differs in sporangiospores, sporangia, sporangiophores, columellae, collars, and rhizoids. The latter is phylogenetically closely related to Cunninghamella intermedia, but morphologically differs in sporangiola and colonies. They were described and illustrated.