CORESTA Meeting, Agronomy/Phytopathology, 2015, Izmir, Turkey, APW 03

Transcriptomic and metabolomic studies reveal spatiotemporal switches of primary and secondary metabolism during leaf senescence of tobacco

LI Wei(1); ZHANG Hailiang(1); LIU Cheng(1); DU Yongmei(1); GAO Xiaoming(1); WANG Guodong(2); GUO Yongfeng(1)
(1) Tobacco Research Institute, Chinese Academy of Agricultural Sciences, Qingdao, P.R. China; (2) Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, P.R. China

Several features of tobacco (Nicotiana tabacum) make it a unique system in studying the metabolome of leaf senescence: 1) as topping being a routine agricultural practice, sequential senescence of leaves at different positions (leaves at lower positions senesce first) makes tobacco useful in studying nutrient remobilisation from old leaves to younger leaves at the top; 2) tobacco has a rich secondary metabolism. In this study the metabolome of tobacco leaf senescence was analysed through profiling of ~80 major metabolites of leaf samples from three representative positions at eight different time points. The metabolomic analysis was supplemented with RNA-seq data from the same leaf samples. Comprehensive analyses on metabolite accumulation and expression changes of enzyme-encoding genes in corresponding metabolic pathways indicated a significant up-regulation of the tricarboxylic acid cycle and related metabolism of sugars, amino acids and fatty acids, suggesting the importance of energy metabolism during leaf senescence. Taken together with an overall up-regulation of the gene expression machinery including ribosomal proteins and RNA polymerases, results from this study support leaf senescence being an exceedingly active process - with senescing leaves having higher activities of gene expression and energy metabolism than young leaves. Other changes of the metabolome during tobacco leaf senescence include increased biosynthesis of nicotine and chlorogenic acid. Our results also suggest that a number of compounds seem to be transported from senescing leaves at lower positions to younger leaves at upper positions. This includes glutamine, sucrose, 2-furoic acid, 4-hydroxy-3-methoxybenzoic acid, caffic acid, chlorogenic acid, phenylalanine, D-turanose, guanosine, hydroquinone, L-cysteine, L-mimosine, L-tyrosine, melibiose, m-hydroxybenzoic acid, nicotine, nicotinic acid, uracil, and 4-hydroxybenzoic acid, some of which could play a role in nutrient remobilisation.