Transcriptome-Based Elucidation of Molecular Mechanism Underlying Cold Tolerance of Trifoliate Orange (Poncirus trifoliata (L.) Raf.) and Exploration of Cold-Responsive Genes

Trifoliate orange (Poncirustrifoliata (L.) Raf.)is extremely cold hardy after a full acclimation; however the underlying molecular mechanisms underlying this plant remain poorly understood. In this study, we first generate a transcriptome of trifoliate orange and then perform global transcriptome profilesin response to cold (4^oC) by high-throughput sequencing. Sequences derived from cold-treated and control plants were mapped to the assembled transcriptome, resulting in the identification of 5,549 differentially expressed genes (DEGs). These comprised 600 (462 up-regulated, 138 down-regulated), 2,346 (1,631 up-regulated, 715 down-regulated), and 5,177 (2,702 up-regulated, 2,475 down-regulated) genes from the cold-treated samples at 6, 24 and 72 h, respectively, when compared with the control. Plant hormone signal transduction, plant-pathogen interaction, and secondary metabolism were the most significantly enriched GO categories amongstin the DEGs. A total of 60 transcription factors were shown to be cold responsive. In addition, a number of genes involved in the catabolism and signaling of hormones, such as abscisic acid and ethylene, were affected by the cold stress. Meanwhile, levels of polyamine were progressively increasedunder cold, consistent with up-regulation of an arginine decarboxylase gene. We further characterize the function of one of these cold-responsive transcription factors using transgenic approach.