Elongator is a histone acetyltransferase (HAT) complex associated with RNA polymerase II (RNAPII) to facilitate transcription elongation. It consists of subunits Elp1-6, with Elp3 conferring HAT activity. Elongator is conserved in yeast, plants and humans. In humans, mutations in Elp genes cause neuronal diseases. In plants, Elongator is a positive regulator of cell proliferation during leaf and root growth. Consequently, Arabidopsis Elongator mutants (elo) have narrow leaves and short roots; additionally, germination, vegetative growth and reproductive development are also affected. Mutants have altered auxin signaling, and a number of auxin-related genes are among those differentially expressed in the mutant. Only two genes have been confirmed as targeted by Elongator during RNAPII transcription elongation, including the light-regulated auxin response regulator IAA3/SHY2. Overall design: Four-day-old darkness-grown Arabidopsis seedlings of the elo3-6 mutant and wild-type (reference sample) were illuminated for 1 hour with red or far-red light or kept in darkness (light treatment control). Each experiment consisted of six samples: two genotypes x three light conditions. Four biological replicates were performed resulting in 24 samples in total. Seedlings were grown on half-strength MS medium without sucrose. Total RNA was isolated using the Qiagen RNeasy Plant Mini Kit with on-column DNase digestion. The manufacturer protocol was followed, except four instead of two RPE washes were performed to improve the A260/A230 ratio in the resulting RNA samples. For microarrays, the Agilent-021169 Arabidopsis platform was used and the analysis was performed according to a loop design. Gene expression levels were compared between the mutant and wild-type seedlings exposed to the same light conditions or between seedlings of the same genotype non-illuminated and illuminated with red or far-red light.