Abstract
Leaf senescence is an important process of growth and development in plant, and it is a programmed decline controlled by a series of genes. In this study, the biochemical properties and transcriptome at five maturity stages (M1∼M5) of tobacco leaves were analyzed to reveal the dynamic changes in leaf senescence of tobacco. A total of 722, 1,534, 3,723, and 6,933 genes were differentially expressed (DEG) between M1 and M2, M1 and M3, M1 and M4, and M1 and M5, respectively. Significant changes of nitrogen, sugars, and the DEGs related to metabolite accumulation were identified, suggesting the importance of energy metabolism during leaf senescence. Gene Ontology (GO) analysis found that DEGs were enriched in biosynthetic, metabolic, photosynthesis, and redox processes, and especially, the nitrogen metabolic pathways were closely related to the whole leaf senescence process (M1∼M5). All the DEGs were grouped into 12 expression profiles according to their distinct expression patterns based on Short Time-series Expression Miner (STEM) software analysis. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis found that these DEGs were enriched in pathways of carbon metabolism, starch and sucrose metabolism, nitrogen metabolism, and photosynthesis among these expression profiles. A total of 30 core genes were examined by Weight Gene Co-expression Network Analysis (WGCNA), and they appeared to play a crucial role in the regulatory of tobacco senescence. Our results provided valuable information for further functional investigation of leaf senescence in plants.
Highlights
Leaf senescence is an important trait that affects the biomass accumulation and nutritional value of agricultural crops
Chlorophyll concentration was used to measure the photosynthetic capacity of leaves at five stages, and the significant declining tendency of the chlorophyll content was observed from M1 to M5 (Figure 1B)
It was reported that leaf senescence is driven by a series of genes senescenceassociated genes (SAGs) (Gan and Amasino, 1997), and sugar accumulation could induce the expression of senescenceassociated genes (SAGs) in the early stage of senescence, whereas the expression of SAGs would be inhibited by the sugar in the later stage of senescence (Paul and Pellny, 2003)
Summary
Leaf senescence is an important trait that affects the biomass accumulation and nutritional value of agricultural crops. Common tobacco (Nicotiana tabacum L.) is regarded as an ideal model organism to investigate leaf senescence. The study of tobacco leaf senescence and its internal material transport provides an important platform for understanding tobacco plant growth and development. Leaf senescence is a complicated developmental process, which is regulated by internal genetic program and other environmental signals (Uzelac et al, 2016). Leaf senescence of tobacco is a complex process involving many molecular events along with physiological and biochemical changes, and these changes are driven by differential expression of thousands of genes under the control of highly regulated genetic procedures (Masclaux et al, 2000; Gregersen and Holm, 2007). To improve leaf quality and yield, a common cultivation practice of topping is used to regulate the nutrient distribution by changing the sink-to-source transition of the leaves and increase the dry matter accumulation in leaves (Weeks and Seltmann, 1986)
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