Abstract
Camellia (C.) oleifera Abel. is an evergreen small arbor with high economic value for producing edible oil that is well known for its high level of unsaturated fatty acids. The yield formation of tea oil extracted from fruit originates from the leaves, so leaf senescence, the final stage of leaf development, is an important agronomic trait affecting the production and quality of tea oil. However, the physiological characteristics and molecular mechanism underlying leaf senescence of C. oleifera are poorly understood. In this study, we performed physiological observation and de novo transcriptome assembly for annual leaves and biennial leaves of C. oleifera. The physiological assays showed that the content of chlorophyll (Chl), soluble protein, and antioxidant enzymes including superoxide dismutase, peroxide dismutase, and catalase in senescing leaves decreased significantly, while the proline and malondialdehyde concentration increased. By analyzing RNA-Seq data, we identified 4645 significantly differentially expressed unigenes (DEGs) in biennial leaves with most associated with flavonoid and phenylpropanoid biosynthesis and phenylalanine metabolism pathways. Among these DEGs, 77 senescence-associated genes (SAGs) including NOL, ATAF1, MDAR, and SAG12 were classified to be related to Chl degradation, plant hormone, and oxidation pathways. The further analysis of the 77 SAGs based on the Spearman correlation algorithm showed that there was a significant expression correlation between these SAGs, suggesting the potential connections between SAGs in jointly regulating leaf senescence. A total of 162 differentially expressed transcription factors (TFs) identified during leaf senescence were mostly distributed in MYB (myeloblastosis), ERF (Ethylene-responsive factor), WRKY, and NAC (NAM, ATAF1/2 and CUCU2) families. In addition, qRT-PCR analysis of 19 putative SAGs were in accordance with the RNA-Seq data, further confirming the reliability and accuracy of the RNA-Seq. Collectively, we provide the first report of the transcriptome analysis of C. oleifera leaves of two kinds of age and a basis for understanding the molecular mechanism of leaf senescence.
Highlights
Camellia (C.) oleifera Abel. is an evergreen small arbor within the genus Camellia of the familyTheaceae
In the present study, by using Quantitative Real-Time PCR (qRT-PCR), we found that the expression levels of key transcription factors such as CoMYBL-1 and CoNAC59 changed significantly, which was in good accordance with the transcriptome data, suggesting that TFs play important roles in C. oleifera leaf senescence based on the transcriptional level
Our results present a transcriptome analysis that combined physiological data and phenotypic observation, which contributes to the understanding of gene expression profiling underlying leaf senescence of C. oleifera
Summary
Camellia (C.) oleifera Abel. is an evergreen small arbor within the genus Camellia of the familyTheaceae. With the growing demand for high-quality edible oil, the low production of tea oil can no longer meet the market demand, so increasing the output of C. oleifera has always been one of the most urgent problems to be solved in the research of this species [6]. Many researches have shown that leaf senescence is crucial to limit the yield and quality of tree species [7]. This process is tightly regulated by both endogenous factors such as leaf age, the state of plant hormones, and the stages of growth and development as well as external factors mainly including diverse environmental conditions like drought and salinity [8]. Many advancements have been made in the research on leaf senescence at the molecular level, and a large number of SAGs have been identified including
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