Transcriptomic Analyses of Camellia oleifera ‘Huaxin’ Leaf Reveal Candidate Genes Related to Long-Term Cold Stress

Abstract

‘Huaxin’ is a new high-yielding timber cultivar of Camellia oleifera of high economic value, and has been widely cultivated in the red soil hilly region of Hunan Province of the People´s Republic of China in recent years. However, its quality and production are severely affected by low temperatures during flowering. To find genes related to cold tolerance and further explore new candidategenes for chilling-tolerance, Illumina NGS (Next Generation Sequencing) technology was used to perform transcriptomic analyses of C. oleifera ‘Huaxin’ leaves under long-term cold stress. Nine cDNA libraries were sequenced, and 58.31 Gb high-quality clean reads were obtained with an average of 5.92 Gb reads for each sample. A total of 191,150 transcripts were obtained after assembly. Among them, 100,703 unigenes were generated, and 44,610 unigenes were annotated. In total, 1564 differentially expressed genes (DEGs) were identified both in the A_B and A_C gene sets. In the current study, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed, andrevealed a group of cold-responsive genes related to hormone regulation, photosynthesis, membrane systems, and osmoregulation; these genes encoded many key proteins in plant biological processes, such as serine/threonine-protein kinase (STPK), transcription factors (TFs), fatty acid desaturase (FAD), lipid-transfer proteins (LTPs), soluble sugars synthetases, and flavonoid biosynthetic enzymes. Some physiological indicators of C. oleifera ‘Huaxin’ were determined under three temperature conditions, and the results were consistent with the molecular sequencing. In addition, the expression levels of 12 DEGs were verified using quantitative real-time polymerase chain reaction (qRT-PCR). In summary, the results of DEGs analysis together with qRT-PCR tests contribute to the understanding of cold tolerance and further exploring new candidate genes for chilling-tolerance in molecular breeding programs of C. oleifera ‘Huaxin’.

Transcriptome sequence and physiological analysis revealed the roles of carotenoids and photosynthesis under low temperature combined with low-light stress on pepper (Capsicum annuum L.)

“…5, 2S) and numerous DEGs of both varieties significantly enriched in photosynthesis (sly00195), photosynthesis-antenna proteins (sly00196), and porphyrin and chlorophyll metabolism (sly00860). Therefore, photosynthesis is likely to be a predominant process in response to LL stress of pepper seedlings, which agrees with the findings in Magnolia wufengensis, Camellia oleifera 'Huaxin', and pea (Lucau-Danila et al 2012, Deng et al 2019, Wu et al 2020. The light-harvesting oxygenic photosynthesis protein present in all eukaryotic organisms mainly includes the light-harvesting complex (Lhc) family members.…”

“…In KEGG pathway analysis, genes involved in LL stress response were predicted to function in photosynthesis, photosynthesis-antenna proteins, carbon metabolism, phenylpropanoid biosynthesis, carbon fixation in photosynthetic organisms, porphyrin and chlorophyll metabolism, glyoxylate and dicarboxylate metabolism, cysteine and methionine metabolism (Fig. 3); a similar result was observed in Camellia oleifera 'Huaxin' leaf under cold stress, which also identified the genes involved in photosynthesis (Wu et al 2020). Meanwhile, oxidative phosphorylation, steroid biosynthesis, glutathione metabolism, amino sugar and nucleotide sugar metabolism, glycolysis/gluconeogenesis, and phenylalanine metabo-lism were significantly enriched in X2 but not in H2, indicating that X2 is more tolerant to LL.…”

“…6). Wu et al (2020) also found a significant decrease in Chl, PN, and ETR as a result of photoinhibition and downregulation of Lhca and Lhcb under 6℃ in two-year-old C. oleifera plants. Also, four genes in the photosynthesis pathway were related to photosystem complex structure in maize treated under 4℃ for 24 h, showing cold stress impaired the photosystem structure and resulted in low values of Fv/Fm (Li et al 2019), which is consistent with our study.…”

Comparative study on fruit development and oil synthesis in two cultivars of Camellia oleifera

“…A total 24 samples were rapidly frozen in liquid nitrogen and stored at -80 °C. The purity, concentration, and integrity of the RNA samples were assessed using agarose gel electrophoreses and the Nanodrop 2500 instrument (Thermo Fisher Scientific, USA) to ensure that they were suitable for transcriptome sequencing [ 4 , 31 ].…”

“…From 1978 to 2009, our C. oleifera research team conducted a comparative regional assessment of 84 C. oleifera clones and selected two cultivars with the most favorable traits (big fruit, high yield, high seed oil content, etc. ), which were named the ‘Huashuo’ and ‘Huajin’ cultivars by the Forest Variety Committee of the State Forestry Administration [ 4 ]. Both cultivars are characterized by large fruits, high and stable yields and strong resistance (average fruit size of C. oleifera is 18.1 g in China) [ 14 , 15 ].…”