Lasy-Seq: a high-throughput library preparation method for RNA-Seq and its application in the analysis of plant responses to fluctuating temperatures.

RNA-Seq is a whole-transcriptome analysis method used to research biological mechanisms and functions but its use in large-scale experiments is limited by its high cost and labour requirements. In this study, we have established a high-throughput and cost-effective RNA-Seq library preparation method that does not require mRNA enrichment. The method adds unique index sequences to samples during reverse transcription (RT) that is conducted at a higher temperature (≥62 °C) to suppress RT of A-rich sequences in rRNA, and then pools all samples into a single tube. Both single-read and paired-end sequencing of libraries is enabled. We found that the pooled RT products contained large amounts of RNA, mainly rRNA, causing over-estimations of the quantity of DNA and unstable tagmentation results. Degradation of RNA before tagmentation was found to be necessary for the stable preparation of libraries. We named this protocol low-cost and easy RNA-Seq (Lasy-Seq) and used it to investigate temperature responses in Arabidopsis thaliana. We analysed how sub-ambient temperatures (10-30 °C) affected the plant transcriptomes using time-courses of RNA-Seq from plants grown in randomly fluctuating temperature conditions. Our results suggest that there are diverse mechanisms behind plant temperature responses at different time scales.