Camellia is an economically, ecologically and phylogenetically valuable genus in the family Theaceae. The frequent interspecific hybridization and polyploidization makes this genus phylogenetically and taxonomically under controversial and require detailed investigation. Chloroplast (cp) genome sequences have been used for cpDNA marker development and genetic diversity evaluation. Our research newly sequenced the chloroplast genome of Camellia japonica using Illumina HiSeq X Ten platform, and retrieved five other chloroplast genomes of Camellia previously published for comparative analyses, thereby shedding lights on a deeper understanding of the applicability of chloroplast information. The chloroplast genome sizes ranged in length from 156,607 to 157,166 bp, and their gene structure resembled those of other higher plants. There were four categories of SSRs detected in six Camellia cpDNA sequences, with the lengths ranging from 10 to 17bp. The Camellia species exhibited different evolutionary routes that lhbA and orf188, followed by orf42 and psbZ, were readily lost during evolution. Obvious codon preferences were also shown in almost all protein-coding cpDNA and amino acid sequences. Selection pressure analysis revealed the influence of different environmental pressures on different Camellia chloroplast genomes during long-term evolution. All Camellia species, except C. crapnelliana, presented the identical rate of amplification in the IR region. The datasets obtained from the chloroplast genomes are highly supportive in inferring the phylogenetic relationships of the Camellia taxa, indicating that chloroplast genome can be used for classifying interspecific relationships in this genus.

Styrax japonicus sieb. et Zucc. is widely distributed in China with ornamental and medicinal values. However, the transcriptome of S. japonicus has not yet been reported. In this study, we carried out the first transcriptome analysis of S. japonicus and developed a set of expressed sequence tag–simple sequence repeats (EST–SSRs). We obtained 338,570,222 clean reads in total, of which the mean GC content was 41.58%. In total, 136,071 unigenes were obtained having an average length of 611 bp and 71,226 unigenes were favorably annotated in the database. In total, we identified 55,977 potential EST–SSRs from 38,611 unigenes, of which there was 1 SSR per 6.73 kb. The di-nucleotide repeats (40.40%) were the most identified SSRs. One set of 60 primer pairs was randomly selected, and the amplified products in S. japonicus were validated; 28 primer pairs successfully produced clear amplicons. A total of 21 (35%) polymorphic genic SSR markers were identified between two populations. In total, 15 alleles were detected and the average number was 6. The average of observed heterozygosity and expected heterozygosity was 0.614 and 0.552, respectively. The polymorphism information content (PIC) value fluctuated between 0.074 and 0.855, with a mean value of 0.504, which was also the middle level. This study provides useful information for diversity studies and resource assessments of S. japonicus.

NAC (NAM, ATAF1-2, and CUC2) transcription factors (TFs) play a vital role in plant growth and development, as well as in plant response to biotic and abiotic stressors (Duan et al., 2019; Guerin et al., 2019). Chrysanthemum is a plant with strong stress resistance and adaptability; therefore, a systematic study of NAC TFs in chrysanthemum is of great significance for plant breeding. In this study, 153 putative NAC TFs were identified based on the Chrysanthemum nankingense genome. According to the NAC family in Arabidopsis and rice, a rootless phylogenetic tree was constructed, in which the 153 CnNAC TFs were divided into two groups and 19 subfamilies. Moreover, the expression levels of 12 CnNAC TFs belonging to the OsNAC7 subfamily were analyzed in C. nankingense under osmotic and salt stresses, and different tissues were tested during different growth periods. The results showed that these 12 OsNAC7 subfamily members were involved in the regulation of root and stem growth, as well as in the regulation of drought and salt stresses. Finally, we investigated the function of the CHR00069684 gene, and the results showed that CHR00069684 could confer improved salt and low temperature resistance, enhance ABA sensitivity, and lead to early flowering in tobacco. It was proved that members of the OsNAC7 subfamily have dual functions including the regulation of resistance and the mediation of plant growth and development. This study provides comprehensive information on analyzing the function of CnNAC TFs, and also reveals the important role of OsNAC7 subfamily genes in response to abiotic stress and the regulation of plant growth. These results provide new ideas for plant breeding to control stress resistance and growth simultaneously.

Soil salinization is a crucial factor that impacts plant distribution and growth. Apocynum venetum, an ornamental plant with medicinal value, has shown remarkable salt tolerance. However, the specific mechanisms through which A. venetum responds to salt stress are not yet fully understood. To address this gap, we conducted a study where 10-week-old A. venetum seedlings were subjected to salt stress by irrigating them with a nutrient solution containing varying concentrations of NaCl (0, 100, 200, and 350 mmol·L⁻¹). After the salt stress treatment, various growth indicators (such as plant height, root length, root fresh weight, root dry weight, leaf fresh weight, leaf dry weight, root water content, leaf water content, and root–leaf ratio) as well as physiological indicators (including SOD and CAT activities in both leaves and roots, soluble protein contents in leaves and roots, and chlorophyll and carotene contents in leaves) were determined. In addition, the gene expression profile of roots under salt stress was examined by transcriptome sequencing to explore the mechanism of salt response in A. venetum. Our results show that salt stress led to yellowing and wilting of A. venetum seedling leaves. Furthermore, the chlorophyll and carotenoid contents in the leaves of the 350 mmol·L⁻¹ NaCl-treated group were significantly reduced. Although the leaf and root biomass gradually decreased with an increase in the salt concentration, the root–leaf ratio exhibited a decreasing trend. NaCl stress also caused significant changes in physiological indices in the A. venntum leaves and roots. The activities of superoxide dismutase (SOD) and catalase (CAT) increased in both leaves and roots of the 100 mmol·L⁻¹ NaCl-treated group. The soluble protein content in both leaves and roots increased under the 200 mmol·L⁻¹ NaCl stress. To screen changes in root gene expression, transcriptome sequencing and qRT-PCR were performed. GO and KEGG enrichment analyses revealed that salt stress primarily affects carbohydrate metabolism, MAPK signaling transduction, phytohormone signaling pathways, glyoxylate and dicarboxylate metabolism, and other pathways. This study provides a novel understanding of the growth and physiological response of A. venetum leaf and root to NaCl stress, as well as the changes in the transcription levels in A. venetum root. The results serve as a reference for future research on salt-tolerant mechanisms and molecular breeding of A. venetum.

Rosa rugosa is a deciduous shrub of the rosa family having ecological, economical, and ornamental values. In this study, the cutting seedlings of wild R. rugosa and five cultivated varieties were treated with polyethylene glycol-6000 (PEG-6000) solution to mimic drought stress. The leaf transpiration rate (Tr), photosynthetic rate (Pn), stomatal conductance (Gs), and the relative water content (RWC) of all genotypes decreased under drought stress. Importantly, the Tr in wild R. rugosa (W) was decreased by 29.42% under 5% PEG treatment, whereas that in other varieties was decreased by 57.63%–74.54%. Similarly, the Pn and Gs of genotype W were significantly higher in W than in other genotypes under 5% PEG treatment. The malondialdehyde (MDA) contents in five cultivated varieties were significantly increased under 5%–10% PEG treatments, and that in W was increased under 15% PEG treatment. In summary, the drought resistance of wild R. rugosa was the strongest, followed by that of ZZ, S, and P, and the drought resistance of ZD and F was the poorest. To explore the adaptation characteristics of R. rugosa leaves to drought stress, the leaf surface and microstructure of six genotypes were observed. The characteristics of the wild leaves such as sunken stomata, developed palisade tissue, and low stomatal density may reduce the water loss, resulting in significantly higher drought tolerance than the other five cultivated varieties. This study elucidated the difference of drought resistance among the six R. rugosa genotypes, and enhanced the understanding of the regulatory mechanisms of drought tolerance.