The basic helix-loop-helix transcription factor, PIB, was first identified as a potential regulator of lignification in the stem of Arabidopsis thaliana. The mutants of pib and of it’s closest homolog, pib-like, show altered cell wall composition. The expression of potential target genes were analyzed, however to fully reveal the role of these transcription factors, their target genes and the processes they regulate, a more high-throughput approach, RNA-seq, is being undertaken. Knowing the diurnal expression of PIB, we want to investigate whether the target genes change between day and night cycles, therefore the samples were collected at two time points, at the end of the night and in the middle of the day. RNA isolated from the stem of mature Arabidopsis plants (wild-type, pib and pib-like mutants, and the double mutant) are included in the study.