Background: Olfactory receptors (ORs) can bind odor molecules and play a crucial role in odor sensation. Due to the frequent gains and losses of genes during evolution, the number of OR members varies greatly among different species. However, whether the extent of gene gains/losses varies between marine mammals and related terrestrial mammals has not been clarified, and the factors that might underlie these variations are unknown.Results: To address these questions, we identified more than 10,000 members of the OR family in 23 mammals and classified them into 830 orthologous gene groups (OGGs) and 281 singletons. Significant differences occurred in the number of OR repertoires and OGGs among different species. We found that all marine mammals had fewer OR genes than their related terrestrial lineages, with the fewest OR genes found in cetaceans, which may be closely related to olfactory degradation. ORs with more gene duplications or loss events tended to be under weaker purifying selection. The average gain and loss rates of OR genes in terrestrial mammals were higher than those of mammalian gene families, while the average gain and loss rates of OR genes in marine mammals were significantly lower and much higher than those of mammalian gene families, respectively. Additionally, we failed to detect any one-to-one orthologous genes in the focal species, suggesting that OR genes are not well conserved among marine mammals.Conclusions: Marine mammals have experienced large numbers of OR gene losses compared with their related terrestrial lineages, which may result from the frequent birth-and-death evolution under varied functional constrains. Due to their independent degeneration, OR genes present in each lineage are not well conserved among marine mammals. Our study provides a basis for future research on the olfactory receptor function in mammals from the perspective of evolutionary trajectories.

Salvia castanea, a wild plant species is adapted to extreme Qinghai-Tibetan plateau (QTP) environments. It is also used for medicinal purposes due to high ingredient of tanshinone IIA (T-IIA). Despite its importance to Chinese medicinal industry, the mechanisms associated with secondary metabolites accumulation (i.e. T-IIA and rosmarinic acid (RA)) in this species have not been characterized. Also, the role of special underground tissues in QTP adaptation of S. castanea is still unknown. We explored the phenomenon of periderm-like structure in underground stem center of S. castanea with an aim to unravel the molecular evolutionary mechanisms of QTP adaptation in this species. Morphologic observation and full-length transcriptome of S. castanea plants were conducted. Comparative genomic analyses of S. castanea with other 14 representative species were used to reveal its phylogenetic position and molecular evolutionary mechanisms. RNA-seq and WGCNA analyses were applied to understand the mechanisms of high accumulations of T-IIA and RA in S. castanea tissues. Based on anatomical observations, we proposed a “trunk-branches” developmental model to explain periderm-like structure in the center of underground stem of S. castanea. Our study suggested that S. castanea branched off from cultivated Danshen around 16 million years ago. During the evolutionary process, significantly expanded orthologous gene groups, 24 species-specific and 64 positively selected genes contributed to morphogenesis and QTP adaptation in S. castanea. RNA-seq and WGCNA analyses unraveled underlying mechanisms of high accumulations of T-IIA and RA in S. castanea and identified NAC29 and TGA22 as key transcription factors. We proposed a “trunk-branches” developmental model for the underground stem in S. castanea. Adaptations to extreme QTP environment in S. castanea are associated with accumulations of high secondary metabolites in this species.

Background: Continuous monocropping can affect the physicochemical and biological characteristics of cultivated soil. Sophora flavescens is a valuable herbal medicine and sensitive to continuous monocropping. Currently, diversity patterns of soil microbial communities in soil continuous monocropping with S. flavescens have not been extensively elucidated. Results: In this study, comparative 16S rDNA and internal transcribed spacer (ITS) MiSeq sequencing analyses were used to examine the taxonomic community structure and microbial diversity in nonrhizosphere soil (CK) and rhizosphere soils (SCC, TCC, and FCC) sampled from fields that had undergone two, three, and five years of continuous monocropping, respectively. Among the microbial communities, a decreased abundance of Acidobacteria and increased abundances of Proteobacteria and Bacteroidetes were found with the increase in monocropping years of S. flavescens. As the continuous monocropping time increased, the diversity of the bacterial community decreased, but that of fungi increased. Redundancy analysis also showed that among the properties of the rhizosphere soil, the available phosphorus, organic matter, total nitrogen, and sucrase had the greatest impacts on the diversity of the rhizosphere microbial community. Moreover, a biomarker for S. flavescens soil was also identified using the most differentially abundant bacteria and fungi in soil samples. Conclusions: Our study indicates that long-term monocropping exerted great impacts on microbial community distributions and soil physicochemical properties. The relationship between microbial community and physicochemical properties of rhizosphere soil would help clarify the side effects of continuous S. flavescens monocropping. Our study may aid in uncovering the theoretical basis underlying obstacles to continuous monocropping and provide better guidance for crop production.

Volatile organic compounds (VOCs) play important roles in the regulation of plant growth and pathogen resistance. However, little is known about the influence of VOCs released from endophytic strains (Burkholderia pyrrocinia strain JK-SH007) on controlling pathogens or inducing systemic resistance in poplar. In this study, we found that VOCs produced by strain JK-SH007 inhibit three poplar canker pathogens (Cytospora chrysosperma, Phomopsis macrospora, and Fusicoccum aesculi) and promote defense enzyme activity and malondialdehyde (MDA) and total phenol (TP) accumulation. Thirteen kinds of VOC components were identified using the solid-phase microextraction combined with gas chromatography-mass spectrometry method. Dimethyl disulfide (DMDS) accounted for the largest proportion of these VOCs. Treatments of poplar seedlings with different volumes of VOC standards (DMDS, benzothiazole, dimethylthiomethane, and phenylacetone) showed that DMDS had the greatest effects on various defense enzyme activities and MDA and TP accumulation. We also found that the inhibitory effect of the VOCs on the three pathogens was gradually enhanced with increasing standard volume. Moreover, the treatment of samples with DMDS significantly reduced the severity and development of the disease caused by three poplar canker pathogens. Comparative transcriptomics analysis of poplar seedlings treated with DMDS showed that there were 1,586 differentially expressed genes in the leaves and stems, and quantitative PCR showed that the gene expression trends were highly consistent with the transcriptome sequencing results. The most significant transcriptomic changes induced by VOCs were related to hormone signal transduction, transcriptional regulation of plant–pathogen interactions, and energy metabolism. Moreover, 137 transcription factors, including members of the ethylene response factor, NAC, WRKY, G2-like, and basic helix-loop-helix protein families, were identified to be involved in the VOC-induced process. This study elucidates the resistance induced by Burkholderia pyrrocinia strain JK-SH007 to poplar canker at the molecular level and can make possible a new method for the comprehensive prevention and control of poplar disease.