An Intestinal Symbiotic Bacterial Strain of Oscheius chongmingensis Modulates Host Viability at Both Global and Post-Transcriptional Levels.

A rhabditid entomopathogenic nematode (EPN), Oscheius chongmingensis, has a stable symbiotic relationship with the bacterial strain Serratia nematodiphila S1 harbored in its intestines and drastically reduced viability when associated with a non-native strain (186) of the same bacterial species. This nematode is thus a good model for understanding the molecular mechanisms and interactions involved between a nematode host and a member of its intestinal microbiome. Transcriptome analysis and RNA-seq data indicated that expression levels of the majority (8797, 87.59%) of mRNAs in the non-native combination of O. chongmingensis and S. nematodiphila 186 were downregulated compared with the native combination, including strain S1. Accordingly, 88.84% of the total uniq-sRNAs mapped in the O. chongmingensis transcriptome were specific between the two combinations. Six DEGs, including two transcription factors (oc-daf-16 and oc-goa-1) and four kinases (oc-pdk-1, oc-akt-1, oc-rtk, and oc-fak), as well as an up-regulated micro-RNA, oc-miR-71, were found to demonstrate the regulatory mechanisms underlying diminished host viability induced by a non-native bacterial strain. Oc-rtk and oc-fak play key roles in the viability regulation of O. chongmingensis by positively mediating the expression of oc-daf-16 to indirectly impact its longevity and stress tolerances and by negatively regulating the expression of oc-goa-1 to affect the olfactory chemotaxis and fecundity. In response to the stress of invasion by the non-native strain, the expression of oc-miR-71 in the non-native combination was upregulated to downregulate the expression of its targeting oc-pdk-1, which might improve the localization and activation of the transcription factor DAF-16 in the nucleus to induce longevity extension and stress resistance enhancement to some extent. Our findings provide novel insight into comprehension of how nematodes deal with the stress of encountering novel potential bacterial symbionts at the physiological and molecular genetic levels and contribute to improved understanding of host-symbiont relationships generally.

Oscheius microvilli n. sp. (Nematoda: Rhabditidae): A Facultatively Pathogenic Nematode from Chongming Island, China.

A new species, Oscheius microvilli n. sp., was found on Chongming Island (Shanghai, China). The new species is morphologically similar to the type strain of Oscheius myriophilus, but can be distinguished from it and other species of Oscheius on the basis of unique morphological characteristics of the bursa as well as male papillae. In this new species, the male bursal papillar formula is 2, 1, 3, 3 with everted tips in the first, fifth, and seventh pairs. The bursal rim is jagged, joins together anterior to the spicules, and is partially extended and decorated with microvilli. The spicules are incompletely separated, and the tail does not extend beyond the bursa. Phylogenetic trees of 18S rDNA and internal transcribed spacer indicate that the new species belongs to the insectivora group of the genus Oscheius; it is most closely related to O. myriophilus, and the two species can be distinguished on the basis of their different body length, morphological features of the bursa, and molecular data. The new species is facultatively associated with a bacterial strain of Serratia. The LC50 of this novel nematode against Galleria mellonella was 69.1 dauer juveniles per milliliter after 48 hr of infection.

A New Species of Pristionchus (Rhabditida: Diplogastridae) and Its Bacterial Symbiont from Yixing, China.

A new nematode species, Pristionchus entomophilus n. sp., was collected during a soil sample survey in Yixing of Jiangsu province, eastern China. P. entomophilus n. sp. is distinguished by its unique characteristics. This new species is mainly hermaphroditic, with males seldom found. The new nematode has a similar body length but has much narrower body width compared with P. pacificus. Its body is covered with longitudinal ridges: 12 ridges on head, 13 or 14 ridges in the middle, 11 and 7 ridges in front and rear of the anus, respectively. The eurystomatous form mouth includes a triangular dorsal tooth, a large claw-like right subventral tooth, and a row of five ventral denticles placed opposite the dorsal tooth. Only eight pairs of genital papillae and a pair of phasmids are present in the tail of the male as the sixth pair of papillae having seemingly been degenerated and lost. Molecular phylogenetic trees based on 18S rDNA confirmed that the new species belongs to the genus Pristionchus and is most closely related to P. pacificus. Moreover, the new species was found to be occasionally associated with the entomopathogenic bacterial strain 09FLYB1 of Serratia nematodophila and be able to stably transfer the bacterial strain for several generations.

Identification and transcriptome analysis of a photosynthesis deficient mutant of Populus davidiana Dode.

Photosynthesis is the main source of energy for plants to sustain growth and development. Abnormalities in photosynthesis may cause defects in plant development. The elaborate regulatory mechanism underlying photosynthesis remains unclear. In this study, we identified a natural mutant from the Greater Khingan Mountains and named it as "1-T". This mutant had variegated leaf with irregular distribution of yellow and green. Chlorophyll contents and photosynthetic capacity of 1-T were significantly reduced compared to other poplar genotypes. Furthermore, a transcriptome analysis revealed 3269 differentially expressed genes (DEGs) in 1-T. The products of the DEGs were enriched in photosystem I and photosystem II. Three motifs were significantly enriched in the promoters of these DEGs. Yeast one-hybrid, Electrophoretic mobility shift assays and tobacco transient transformation experiments indicated that PdGLKs may bind to the three motifs. Further analysis indicated that these photosystem related genes were also significantly down-regulated in PdGLK-RNAi poplars. Therefore, we preliminarily concluded that the down-regulation of PdGLKs in 1-T may affect the expression of photosystem-related genes, resulting in abnormal photosystem development and thus affecting the growth and development. Our results provide new insights into the molecular mechanism of photosynthesis regulating plant growth.