Phytosulfokine-α (PSK-α) is a newly discovered short peptide that acts as a phytohormone in various plants. Previous studies have shown that PSK-α is critical for many biological processes in plants, such as cell division and differentiation, somatic embryogenesis, pollen germination and plant resistance. In this study, we cloned two PSK homolog genes from Cunninghamia lanceolata (Lamb.) Hook (Chinese fir), ClPSK1 and ClPSK2, and characterized their function in root development. Quantitative RT-PCR analyses showed that both ClPSK1 and ClPSK2 were expressed in vegetative organs, mainly in roots. Transgenic Arabidopsis plants overexpressing ClPSK1 or ClPSK2 showed a higher frequency of adventitious root formation and increased root length. The expression of genes in Arabidopsis that are involved in stem cell activity (PLT1, PLT2 and WOX5), radial organization of the root (SHR and SCR) and cell cycle (CYCB1;1, CYCD4;1, CDKB1;1 and RBR) were significantly up-regulated, which may contribute to the elongation of the primary root and the formation of adventitious root in transgenic lines. Our results suggest that ClPSKs play an important role during root growth and development.

Larch is widely distributed throughout the world and is an important species for timber supply and the extraction of industrial raw materials. In recent years, the hybrid breeding of Larix kaempferi and Larix olgensis has shown obvious heterosis in quick-growth, stress resistance and wood properties. However, its growth and development cycle is too long to meet general production needs. In order to shorten the breeding cycle, we have for the first time successfully established and optimized a somatic embryogenesis system for Larix kaempferi × Larix olgensis. We found that the highest rate of embryonal-suspensor mass (ESM) induction was observed when late cotyledonary embryos were used as explants. The induced ESMs were subjected to stable proliferation, after which abscisic acid (ABA) and polyethylene glycol (PEG) were added to successfully induce somatic embryos. Treatment with PEG and ABA was of great importance to somatic embryo formation and complemented each other’s effect. ABA assisted embryo growth, whereas PEG facilitated the formation of proembryo-like structures. On top of this, we studied in more detail the relationship between redox homeostasis and the efficiency of somatic embryogenesis (frequency of ESM induction). During subculture, we observed the gradual formation of three distinct types of ESM. The Type I ESM is readily able to form somatic embryos. In contrast to type I, the type III ESM suffers from severe browning, contains a higher level of hydrogen peroxide (H₂O₂) and demonstrates a decreased ability to form somatic embryos. External treatment with H₂O₂ decreased the somatic embryogenesis efficiency of Type I and type III ESMs, or the higher the exogenous H₂O₂ content, the lower the resulting somatic embryogenesis efficiency. We found that treatment with the H₂O₂ scavenger DMTU (dimethylthiourea) could significantly increase the somatic embryogenesis efficiency of the type III ESM, as a result of a decline in endogenous H₂O₂ content. Overall, these findings have contributed to setting up a successful somatic embryogenesis system for larch production.

Superoxide dismutase (oxide dismutase) is an enzyme synthesized via the expression of SOD-related genes. It is the first line of defense against oxygen free radicals, and it widely exists in the cytoplasm, chloroplasts, and mitochondria. However, the SOD gene family of woody plant Liriodendron chinense has not been studied. To reveal the potential role of SOD genes, we systematically identified and analyzed the SOD gene family of L. chinense, and investigated the transcriptional responses of LcSOD genes to several abiotic stresses, including cold, heat, and drought. A total of eight SOD genes were identified, namely, five Cu/Zn-SODs, two Fe-SODs, and one Mn-SOD, and they were divided into two subgroups according to phylogenetic analysis, gene structure, and conserved motifs. Cis-acting element analysis reveals various hormones and stress respond as cis-acting elements in the promoters of LcSODs. Gene expression analysis shows that most LcSOD genes were in response to abiotic stresses at the transcriptional level. These results help in clarifying the function of LcSOD genes under abiotic stresses, and provide potential targets for the improvement in abiotic stress tolerance in the endangered L. chinense.

Cunninghamia lanceolata (Lamb.) Hook. (Chinese fir) is an important timber species that is widely cultivated in southern China. However, the shallow root system and weak drought resistance of Chinese fir are not enough to cope with high temperature and drought. In recent years, molecular biology has been used to modify plants to make them more resilient. Therefore, improving heat and drought resistance of Chinese fir by molecular biology technology is one of the best choices, whereas fewer genetic information resources for C. lanceolata limit more comprehensive molecular studies. In this study, single-molecule full-length transcriptome (SMRT) sequencing technology was used to obtain full-length transcriptome data on Chinese fir. A total of 21,331 transcripts were obtained via co-assembly, and 11,094 gene sets were obtained via further de-redundancy. In addition, gene function annotation and gene structure analysis were performed. We also used these data to identify nine heat shock transcription factors (Hsfs) in Chinese fir, and heat stress transcriptome and real-time quantitative polymerase chain reaction (PCR) analyses revealed expression changes in response to heat stress, indicating that these may play roles in heat resistance. These studies have enriched the genetic information resources of Chinese fir, which may be utilized for further species promotion, improvement, and application.