Maize (Zea mays) leaf transcriptome analysis under abiotic stress in wild type and RNA Polymerase IV mutant

Plants have developed complex mechanisms to respond and adapt to abiotic stresses, coupling elaborate modulation of gene expression together with the preservation of genome stability. Epigenetic mechanisms - DNA methylation, chromatin modifications and non coding RNAs - were shown to play a fundamental role in stress-induced gene regulation and may also result in genome destabilization, with the activation and/or the transcription of silenced transposons and retroelements, causing genome rearrangements and novel gene expression patterns. Maize leaf transcriptome was analyzed by total RNA-Seq in both B73 and rmr6 (PolIV mutant involved in siRNA biogenesis and in the RdDM pathway) after drought and salt stress application. Reference annotation based transcript assembly allowed the identification both of new expressed loci and splicing variants, improving the current maize transcriptome annotation. Many antisense transcripts matching on the opposite strand of annotated loci were also identified, while more than the 20% of transcripts represent non coding RNA belonging to four classes: siRNAs, shRNAs, lncRNAs and transposable elements (or their relics). Several lncRNAs are modulated by stress application while TE-related sequences are mainly expressed in rmr6 and up-regulated by the stress. Total RNA-Seq analysis of maize leaves from wt and rmr6-1 mutant plants grown under 1) control conditions, 2) drought stress, 3) salt stress, 4) salt+drought stress. Each condition was investigated in triplicate after 10 days of treatment and after 7 days of recovery. Samples derived from replicates 2 and 3 were pooled and sequenced together