De novo characterization of Platycladus orientalis transcriptome and analysis of its gene expression during aging

Platycladus orientalis in China has a lifespan of one to several thousands of years. The long lifespans of trees have attracted interest in aging at the molecular level. There is little information on how the global process is controlled. In this study, the MDA content, SOD and POD activities were higher in ancient P. orientalis than in 20-year-old Platycladus orientalis , and the content of protein showed the inverse trend. We obtained 48,044 unigenes having an average length of 896 bp from pooled samples of P. orientalis by transcriptome sequencing. Microarray analysis produced a high-resolution age-course profile of gene expression levels in different age of P. orientalis. In total, 418 differentially expressed genes were identified. The use of highly informative clustering revealed distinct time points at which oxidation reduction and photosynthesis pathways changed. Eight clusters with distinctive expression patterns were identified, the expression of metabolism, photosynthesis, oxidation reduction and transporters related genes were downregulated and protein synthesis, transcription, signal transduction and senescence related genes were upregulated with increasing age. Total chlorophyll, chlorophyll a, and chlorophyll b levels were decreased steadily with age. This study discovery of potential candidate genes affecting photosynthesis in different P. orientalis ages and at senescence, and for identification of the functions of genes involved in regulation of photosynthesis. This work also suggests that improving photosynthetic efficiency under field conditions will require the consideration of multiple factors, such as stress responses.