Temporal transcriptome profiling reveals candidate genes involved in cold acclimation of Camellia japonica (Naidong)

Integrative Transcriptomic and Small RNA Analysis Uncovers Key Genes for Cold Resistance in Rice

BACKGROUND/OBJECTIVES

Cold stress is the main environmental factor that affects the growth and development of rice, leading to a decrease in its yield and quality. However, the molecular mechanism of rice's low-temperature resistance remains incompletely understood.

METHODS

In this study, we conducted a joint analysis of miRNA and mRNA expression profiles in the cold-resistant material Yongning red rice and the cold-sensitive material B3 using high-throughput sequencing.

RESULTS

194 differentially expressed miRNAs (DEMIs) and 14,671 differentially expressed mRNAs (DEMs) were identified. Among them, 19 DEMIs, including miR1437, miR1156, miR166, miR1861, and miR396_2 family members, showed opposite expression during the early or late stages of low-temperature treatment in two varieties, while 13 DEMIs were specifically expressed in Yongning red rice, indicating that these miRNAs are involved in rice's resistance to low temperature. In the transcriptome analysis, 218 DEMs exhibited opposite expressions during the early or late stages of low-temperature treatment in two varieties. GO enrichment analysis indicated that these DEMs were enriched in biological processes such as a defense response to fungi, a defense response to bacteria, a plant-type cell wall modification, single-organism cellular processes, a response to chitin, and the regulation of a plant-type hypersensitive response, as well as in cellular components such as the apoplast, nucleus, vacuole, plasma membrane, and plasmodesma. Twenty-one genes were further selected as potential candidates for low-temperature resistance. The joint analysis of miRNA and mRNA expression profiles showed that 38 miRNAs corresponding to 39 target genes were candidate miRNA-mRNA pairs for low-temperature resistance.

CONCLUSIONS

This study provides valuable resources for determining the changes in miRNA and mRNA expression profiles induced by low temperatures and enables the provision of valuable information for further investigating the molecular mechanisms of plant resistance to low temperatures and for the genetic improvement of cold-resistant varieties.

Transcriptome Profiling of Two Camellia japonica Cultivars with Different Heat Tolerance Reveals Heat Stress Response Mechanisms

Camellia (Camellia japonica) is a semi-shaded plant that is highly vulnerable to heat stress. To investigate the mechanisms underlying heat stress in C. japonica, two C. japonica cultivars, "Xiaotaohong" and "Zhuapolian", which exhibit significant differences in heat tolerance, were selected from four common cultivars. The selection methods included phenotypic observations and physiological index detection, including relative electric conductivity (REC), malondialdehyde (MDA) content, superoxide dismutase (SOD) enzyme activity, relative water content (RWC), and chlorophyll content. RNA-seq analysis yielded 980 million reads and identified 68,455 differentially expressed genes (DEGs) in the two C. japonica cultivars during heat stress compared to the control samples. Totals of 12,565 and 16,046 DEGs were differentially expressed at 16 h and 32 h, respectively, in "Xiaotaohong" during heat stress. In "Zhuapolian", 40,280 and 37,539 DEGs were found at 16 h and 32 h, respectively. KEGG enrichment analysis revealed that both cultivars were enriched in the "plant hormone signal transduction" and "circadian rhythm" pathways at two stages, indicating the critical role these pathways play in the heat stress response. The differences in the tolerance between the two cultivars are likely linked to pathways such as "plant hormone signal transduction", "photosynthesis", and "circadian rhythm". Some members of heat shock proteins (HSPs) are associated with the heat stress response. It is speculated that transcription factor families contributing to the tolerance differences include AP2/ERF, C3H, bHLH, bZIP, and MYB-related with a small number of heat shock factors (HSFs) also induced by the stress. In conclusion, these results reveal the changes in the physiological indices and molecular networks of two C. japonica cultivars under heat stress. This study lays the foundation for the breeding of superior heat-resistant C. japonica cultivars and for further molecular research.

Novel insight into anthocyanin metabolism and molecular characterization of its key regulators in Camellia sasanqua

Flower color is a trait that affects the ornamental value of a plant. Camellia sasanqua is a horticultural plant with rich flower color, but little is known about the regulatory mechanism of color diversity in this plant. Here, the anthocyanin profile of 20 C. sasanqua cultivars revealed and quantified 11 anthocyanin derivatives (five delphinidin-based and six cyanidin-based anthocyanins) for the first time. Cyanidin-3-O-(6-O-(E)-p-coumaroyl)-glucoside was the main contributor to flower base color, and the accumulation of cyanidin and delphinidin derivatives differed in the petals. To further explore the molecular mechanism of color divergence, a transcriptome analysis was performed using C. sasanqua cultivars 'YingYueYe', 'WanXia', 'XueYueHua', and'XiaoMeiGui'. The co-expression network related to differences in delphinidin and cyanidin derivatives accumulation was identified. Eleven candidate genes encoding key enzymes (e.g., F3H, F3'H, and ANS) were involved in anthocyanin biosynthesis. Moreover, 27 transcription factors were screened as regulators of the two types of accumulating anthocyanins. The association was suggested by correlation analysis between the expression levels of the candidate genes and the different camellia cultivars. We concluded that cyanidin and delphinidin derivatives are the major drivers of color diversity in C. sasanqua. This finding provides valuable resources for the study of flower color in C. sasanqua and lays a foundation for genetic modification of anthocyanin biosynthesis.

Discovery of New Triterpenoids Extracted from Camellia oleifera Seed Cake and the Molecular Mechanism Underlying Their Antitumor Activity

Theasaponin derivatives, which are reported to exert antitumor activity, have been widely reported to exist in edible plants, including in the seed cake of Camellia oleifera (C.), which is extensively grown in south of China. The purpose of this study was to isolate new theasaponin derivatives from C. seed cake and explore their potential antitumor activity and their underlying molecular mechanism. In the present study, we first isolated and identified four theasaponin derivatives (compounds 1, 2, 3, and 4) from the total aglycone extract of the seed cake of Camellia oleifera by utilizing a combination of pre-acid-hydrolysis treatment and activity-guided isolation. Among them, compound 1 (C1) and compound 4 (C4) are newly discovered theasaponins that have not been reported before. The structures of these two new compounds were characterized based on comprehensive 1D and 2D NMR spectroscopy and high-resolution mass spectrometry, as well as data reported in the literature. Secondly, the cytotoxicity and antitumor property of the above four purified compounds were evaluated in selected typical tumor cell lines, Huh-7, HepG2, Hela, A549, and SGC7901, and the results showed that the ED₅₀ value of C4 ranges from 1.5 to 11.3 µM, which is comparable to that of cisplatinum (CDDP) in these five cell lines, indicating that C4 has the most powerful antitumor activity among them. Finally, a preliminary mechanistic investigation was performed to uncover the molecular mechanism underlying the antitumor property of C4, and the results suggested that C4 may trigger apoptosis through the Bcl-2/Caspase-3 and JAK2/STAT3 pathways, and stimulate cell proliferation via the NF-κB/iNOS/COX-2 pathway. Moreover, it was surprising to find that C4 can inhibit the Nrf2/HO-1 pathway, which indicates that C4 has the potency to overcome the resistance to cancer drugs. Therefore, C1 and C4 are two newly identified theasaponin derivatives with antitumor activity from the seed cake of Camellia oleifera, and C4 is a promising antitumor candidate not only for its powerful antitumor activity, but also for its ability to function as an Nrf2 inhibitor to enhance the anticancer drug sensitivity.

Floral organ transcriptome in Camellia sasanqua provided insight into stamen petaloid

BACKGROUND

The cultivated Camellia sasanqua forms a divergent double flower pattern, and the stamen petaloid is a vital factor in the phenomenon. However, the regulation mechanism remains largely unclear.

RESULTS

Here, a comprehensive comparative transcriptome analysis of the wild-type, "semi-double", "peony double", and "rose double" was performed. The cluster analysis of global gene expression level showed petal and stamen difficulty separable in double flower. The crucial pathway and genes related to double flower patterns regulation were identified by pairwise comparisons and weighted gene coexpression network (WGCNA). Divergent genes expression, such as AUX1 and AHP, are involved in plant hormone signaling and photosynthesis, and secondary metabolites play an important role. Notably, the diversity of a petal-specific model exhibits a similar molecular signature to the stamen, containing extensin protein and PSBO1, supporting the stamen petaloid point. Moreover, the expansion of class A gene activity influenced the double flower formation, showing that the key function of gene expression was probably demolished.

CONCLUSIONS

Overall, this work confirmed the ABCE model and provided new insights for elucidating the molecular signature of double formation.

Multi-Approach Analysis Reveals Pathways of Cold Tolerance Divergence in Camellia japonica

Understanding the molecular mechanism of the cold response is critical to improve horticultural plant cold tolerance. Here, we documented the physiological, transcriptome, proteome, and hormonal dynamics to cold stress in temperate genotype (Tg) and subtropical genotype (Sg) populations of Camellia japonica. Tg C. japonica suffered minimal osmotic and oxidative damage compared to Sg C. japonica under the same cold treatment. Transcriptional and translational differences increased under the cold treatment, indicating that Tg C. japonica was affected by the environment and displayed both conserved and divergent mechanisms. About 60% of the genes responding to cold had similar dynamics in the two populations, but 1,896 transcripts and 455 proteins differentially accumulated in response to the cold between Tg and Sg C. japonica. Co-expression analysis showed that the ribosomal protein and genes related to photosynthesis were upregulated in Tg C. japonica, and tryptophan, phenylpropanoid, and flavonoid metabolism were regulated differently between the two populations under cold stress. The divergence of these genes reflected a difference in cold responsiveness. In addition, the decrease in the abscisic acid (ABA)/gibberellic acid (GA) ratio regulated by biosynthetic signal transduction pathway enhanced cold resistance in Tg C. japonica, suggesting that hormones may regulate the difference in cold responsiveness. These results provide a new understanding of the molecular mechanism of cold stress and will improve cold tolerance in horticultural plants.

Population Genetic Structure Analysis Reveals Significant Genetic Differentiation of the Endemic Species Camellia chekiangoleosa Hu. with a Narrow Geographic Range

In order to protect and utilize the germplasm resource better, it is highly necessary to carry out a study on the genetic diversity of Camellia chekiangoleosa Hu. However, systematic research on population genetics analysis of the species is comparatively rare. Herein, 16 highly variable simple sequence repeat (SSR) markers were used for genetic structure assessment in 12 natural C. chekiangoleosa populations. The genetic diversity of C. chekiangoleosa was low (h = 0.596), within which, central populations (such as Damaoshan (DMS), Sanqingshan (SQS), and Gutianshan (GTS)) at the junction of four main mountain ranges presented high diversity and represented the center of the C. chekiangoleosa diversity distribution; the Hengshan (HS) population in the west showed the lowest diversity, and the diversity of the eastern and coastal populations was intermediate. C. chekiangoleosa exhibited a high level of genetic differentiation, and the variation among populations accounted for approximately 24% of the total variation. The major reasons for this situation are the small population scale and bottleneck effects in some populations (HS and Lingshan (LS)), coupled with inbreeding within the population and low gene flow among populations (Nm = 0.796). To scientifically protect the genetic diversity of C. chekiangoleosa, in situ conservation measures should be implemented for high-diversity populations, while low-diversity populations should be restored by reintroduction.

Transcriptomic and Chemical Analyses Reveal the Hub Regulators of Flower Color Variation from Camellia japonica Bud Sport

Camellia japonica is a woody ornamental plant with multiple flower color variations caused by bud sport; however, the molecular mechanism remains unclear. Here, chemical and transcriptomic analyses of C. japonica were performed with white, pink, red, and dark red flowers caused by bud sport. Seven anthocyanins were detected in these samples, except in C. japonica ’YuDan’ (white petals). The total anthocyanin content of C. japonica ’JinBiHuiHuang’ was the highest, and cyanidin 3-O-β-glucoside (Cy3G) was the main anthocyanin affecting the redness of petals. Furthermore, the ratio of Cy3G and cyanidin-3-O-(6-O-(E)-p-coumaroyl)-B-glucoside) was significantly correlated with the red petal phenotype. In total, 5673 genes were identified as differentially expressed genes (DEGs). The potential co-expression modules related to anthocyanin accumulation were established, which featured transcription factors, anthocyanin biosynthesis, and plant hormone signal transduction. Thirteen structural genes in the anthocyanin biosynthetic pathway were identified as DEGs, most of them were upregulated with deepening of flower redness. An integrated promoter and cluster analysis suggested that CjMYB62, CjMYB52, and CjGATA may play important roles in anthocyanin accumulation. These results provide insight and candidate genes for the transcriptional mechanism responsible for the bud sport phenotype.