Transcriptome differences between 20- and 3,000-year-old Platycladus orientalis   reveal that ROS are involved in senescence regulation

Background: Platycladus orientalis has an extremely long life span of several thousands of years, attracting great interests in the mechanisms involved in such successful senescence regulation and resistance at physiological and molecular levels.
Results: The levels of reactive oxygen species (ROS) were higher in 3,000-year-old than in 20-year-old P. orientalis, and the activities of GR and GSH demonstrated the same trend. We produced and analyzed massive sequence information from pooled samples of P. orientalis through transcriptome sequencing, which generated 51,664 unigenes with an average length of 475 bp. We then used RNA-seq analysis to obtain a high-resolution age–course profile of gene expression in 20- and 3,000-year-old P. orientalis individuals. Totally, 106 differentially expressed genes were obtained, of which 47 genes were downregulated and 59 upregulated in the old tree. These genes were involved in transcription factors, hormone-related responses, ROS scavengers, senescence-related responses, stress response, and defense and possibly play crucial roles in tackling various stresses in the 3,000-year-old P. orientalis during its life time. The expression patterns of genes related to ROS homeostasis further indicated that the high ability of ROS scavenging could be helpful for the 3,000-year-old P. orientalis to resist senescence.
Conclusions: This study provides a foundation for the elucidation of senescence resistance through molecular studies and the discovery of useful genes in P. orientalis.

Keywords
Digital gene expression; Downregulated genes; Old trees; qRT-PCR; ROS scavenging; Reactive oxygen species; RNA-seq analysis; ROS homeostasis; Senescence resistance; Transcriptome sequencing; Unigenes