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Abstract Background Paulownia, an ecologically and economically valuable plant species native to China, is notable for its excellent timber quality and strong adaptability. Among them, Paulownia catalpifolia displays the ability to survive in cold climate, a trait associated with northern China. Yet, the molecular information for its cold-tolerance has not been explored. This study was to investigate the changes in physiological indices and transcript levels of P. catalpifolia following cold exposure, which could provide evidence for revealing whether there were differences in the genetic basis of inducing physiological perturbations between moderate low temperature (MLT) and extreme low temperature (ELT). Results The detection of physiological indices under diverse degrees of chilling stress showed similar patterns of alteration. Enhanced accumulation of osmoregulatory substances, such as soluble sugar and soluble protein, were more conducive under ELT compared to MLT in P. catalpifolia. Moreover, we observed leaf wilting symptoms distinctly after exposure to ELT for 48 h, while this effect was not obvious after MLT exposure for 48 h. Comparative transcriptomic analysis between MLT and ELT demonstrated 13,688 differentially expressed genes (DEGs), most of them appeared after 12 h and 48 h of treatment. GO and KEGG analyses elucidated prominent enrichment in aromatic-L-amino-acid decarboxylase activity term and carbohydrate metabolism pathways. Therefore, it was speculated that the DEGs involved in the above processes might be related to the difference in the contents of soluble protein and soluble sugar between MLT and ELT. Time series clustering analyses further highlighted several key genes engaged in the ‘Glycosyltransferases’, ‘Galactose metabolism’ and ‘Starch and sucrose metabolism’ pathways as well as the ‘tyrosine decarboxylase activity’ term. For instance, cellulose synthase-like A (CLSA2/9), raffinose synthase (RafS2), β-amylase (BAM1) and tyrosine/DOPA decarboxylase (TYDC1/2/5) genes, diverging in their expression trends between MLT and ELT, might significantly affect the soluble sugar and soluble protein abundance within P. catalpifolia. Conclusion Between MLT and ELT treatments, partial overlaps in response pathways of P. catalpifolia were identified, while several genes regulating the accumulation of osmotic adjustment substances had disparate expression patterns. These findings could provide a novel physiological and molecular perspective for P. catalpifolia to adapt to complex low temperature habitats.

Terpene synthases (TPSs) are crucial for the diversification of terpenes, catalyzing the formation of a wide variety of terpenoid compounds. However, genome-wide systematic characterization of TPS genes in Cymbidium ensifolium has not been reported. Within the genomic database of C. ensifolium, we found 30 CeTPS genes for this investigation. CeTPS genes were irregularly distributed throughout the seven chromosomes and primarily expanded through tandem duplications. The CeTPS proteins were classified into three TPS subfamilies, including 17 TPS-b members, 8 TPS-a members, and 5 TPS-c members. Conserved motif analysis showed that most CeTPSs contained DDxxD and RRX8W motifs. Cis-element analysis of CeTPS gene promoters indicated regulation primarily by plant hormones and stress. Transcriptome analysis revealed that CeTPS1 and CeTPS18 had high expression in C. ensifolium flowers. qRT-PCR results showed that CeTPS1 and CeTPS18 were predominantly expressed during the flowering stage. Furthermore, CeTPS1 and CeTPS18 proteins were localized in the chloroplasts. These results lay the theoretical groundwork for future research on the functions of CeTPSs in terpenoid biosynthesis.

By choosing appropriate candidate reference genes (CRGs) and standardizing qPCR data, more accurate experimental data can be obtained. Herein, the expression stability of alpha-tubulin1 (TUA1), beta-tubulin (TUB), beta-tubulin 1 (TUB1), beta-tubulin 5 (TUB5), actin 1 (ACT1), actin 97 (ACT97), molecular chaperone dnaj (DNAJ), adenine phosphoribosyl transferase (APT), and histone H4 (HIS4) genes from Paulownia fortunei (Seem.) Hemsl. under different experimental conditions (different tissues, drought, salinity, Cd, and Cr treatments) was assessed with four statistical tools: RefFinder, BestKeeper, NormFinder, and geNorm. Notably, TUA1 and TUB5 were identified as CRGs for different tissues, ACT97 and TUB1 for drought treatment, ACT97 and APT for salinity treatment, TUB1 and ACT97 for Cd treatment, and DNAJ, TUB1 and TUB5 for Cr treatment. Furthermore, the results of "total" group, V4/V5 > 0.15 and V5/V6 < 0.15 revealed that the CRGs or gene combinations, which could meet all the test conditions, were not easy to identify. To further verify the reliability of CRGs, the expression levels of paulownia fortunei cellulose synthase A catalytic subunit2 (PfCesA2) and paulownia fortunei glutathione reductase (GR) genes were analysed. The expression patterns were different when the unstable CRGs were used for normalization compared to when the stable CRGs and combination were used for normalization. This study will lay a foundation for study on the expression levels of key genes from P. fortunei seedlings.

A method for in vitro culture and rapid propagation of Chirita ophiopogoides was developed using leaves as explants in this study. The results indicated that the medium MS+6-BA 0.1 mg/L+NAA 0.1 mg/L was suitable for bud induc- tion and seedling regeneration from leaves in primary culture. The media MS+0.5 mg/L 6-BA+0.1 mg/L NAA+10% banana+5% potato and MS+0.5 mg/L 6-BA+0.5 mg/L NAA+2% banana were very suitable for callus multiplication and seedling hardening in subculture, and the proliferation coefficients were 7.9 and 5.6 per 60 d respectively. The optimal rooting medium was MS and the rooting rate was 100% on day 30 of culture. The rooted plantlets of C. ophiopogoides were transplanted in greenhouse with humus soil and 92.5% survived. Theoretically, using the rapid propagation system, about 20 176 seedlings can be reproduced from a sterile plantlet in a year. [ABSTRACT FROM AUTHOR]