Backgrounds: Paphiopedilum is an important genus of the orchid family Orchidaceae and has high horticultural value. The wild populations are under threat of extinction because of overcollection and habitat destruction. Mature seeds of most Paphiopedilum species are difficult to germinate, which severely restricts their germplasm conservation and commercial production. The factors inhibiting germination are largely unknown. Results: In this study, large amounts of non-methylated lignin accumulated during seed maturation of Paphiopedilum armeniacum (P. armeniacum), which negatively correlates with the germination rate. The transcriptome profiles of P. armeniacum seed at different development stages were compared to explore the molecular clues for non-methylated lignin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that a large number of genes associated with phenylpropanoid biosynthesis and phenylalanine metabolism during seed maturation were differentially expressed. Several key genes in the lignin biosynthetic pathway displayed different expression patterns during the lignification process. PAL, 4CL, HCT, and CSE upregulation was associated with C and H lignin accumulation. The expression of CCoAOMT, F5H, and COMT were maintained at a low level or down-regulated to inhibit the conversion to the typical G and S lignin. Quantitative real-time RT-PCR analysis confirmed the altered expression levels of these genes in seeds and vegetative tissues. Conclusions: This work demonstrated the plasticity of natural lignin polymer assembly in seed and provided a better understanding of the molecular mechanism of seed-specific lignification process.

WRKY proteins are a large superfamily of transcription factors that are involved in diverse biological processes including development, as well as biotic and abiotic stress responses in plants. WRKY family proteins have been extensively characterized and analyzed in many plant species, including Arabidopsis, rice, and poplar. However, knowledge on WRKY transcription factors in Santalum album is scarce. Based on S. album genome and transcriptome data, 64 SaWRKY genes were identified in this study. A phylogenetic analysis based on the structures of WRKY protein sequences divided these genes into three major groups (I, II, III) together with WRKY protein sequences from Arabidopsis. Tissue-specific expression patterns showed that 37 SaWRKY genes were expressed in at least one of five tissues (leaves, roots, heartwood, sapwood, or the transition zone), while the remaining four genes weakly expressed in all of these tissues. Analysis of the expression profiles of the 42 SaWRKY genes after callus was initiated by salicylic acid (SA) and methyl jasmonate (MeJA) revealed that 25 and 24 SaWRKY genes, respectively, were significantly induced. The function of SaWRKY1, which was significantly up-regulated by SA and MeJA, was analyzed. SaWRKY1 was localized in the nucleus and its overexpression improved salt tolerance in transgenic Arabidopsis. Our study provides important information to further identify the functions of SaWRKY genes and to understand the roles of SaWRKY family genes involved in the development and in SA- and MeJA-mediated stress responses.

The Asian giant soft-shelled turtle, Pelochelys cantorii (Trionychidae), is one of the largest aquatic turtles in China and was designated as a First-Grade Protected Animal in China in 1989. Previous investigation based on a combination of Illumina short-read, PacBio long-read and Hi-C scaffolding technologies acquired a high-quality chromosome-level genome of Pc. cantorii. In this study, comparative genomic analysis between Pc. cantorii and 16 other vertebrate genomes indicated that turtles separated from the ancestor of archosaurians approximately 256.6 (95% highest posterior density interval, 263.6–251.9) million years ago (Mya) (Upper Permian to Triassic) and that Pc. cantorii separated from the ancestor of Pd. sinensis and R. swinhoei approximately 59.3 (95% highest posterior density interval, 64.3–54.3) Mya. Moreover, several candidate genes, such as VWA5A, ABCG2, A2M and IGSF1, associated with tumor suppression, growth and age were expanded, implicating their potential roles in the exceptional longevity of turtles. This new chromosome-level assembly has important scientific value in the study of conservation of Pc. cantorii and also enriches the evolutionary investigation of turtle species.

Saposhnikovia divaricata, a well-known Chinese medicinal herb, is the sole species under the genus Saposhnikovia of the Apiaceae subfamily Apioideae Drude. However, information regarding its genetic diversity and evolution is still limited. In this study, the first complete chloroplast genome (cpDNA) of wild S. divaricata was generated using de novo sequencing technology. Similar to the characteristics of Ledebouriella seseloides, the 147,834 bp-long S. divaricata cpDNA contained a large single copy, a small single copy, and two inverted repeat regions. A total of 85 protein-coding, 8 ribosomal RNA, and 36 transfer RNA genes were identified. Compared with five other species, the non-coding regions in the S. divaricata cpDNA exhibited greater variation than the coding regions. Several repeat sequences were also discovered, namely, 33 forward, 14 reverse, 3 complement, and 49 microsatellite repeats. Furthermore, phylogenetic analysis using 47 cpDNA sequences of Apioideae members revealed that L. seseloides and S. divaricata clustered together with a 100% bootstrap value, thereby supporting the validity of renaming L. seseloides to S. divaricata at the genomic level. Notably, S. divaricata was most closely related to Libanotis buchtormensis, which contradicts previous reports. Therefore, these findings provide a valuable foundation for future studies on the genetic diversity and evolution of S. divaricata.