Expression levels of maize miRNA genes assessed using Solexa sequencing.

Small RNA libraries were constructed for a variety of maize tissues and sequenced using Illumina's sequencing-by-synthesis technology [45]. The level of expression of miRNA gene families in each tissue was assessed by counting the number of 18–22 nt reads mapping to each family, normalized by the total number of 18–22 nt reads in the respective libraries. Counts are in Reads per Million (RPM).