Over-representation analysis of gene functional classes that are differentially expressed in ES and PES internodes of alfalfa genotypes 252 and 1283. Columns: A, Genes up-regulated in 252 ES; B, Genes up-regulated in 252 PES; C, Genes down-regulated in 252 ES; D, Genes down-regulated in 252 PES compared to 1283 ES or PES. Blue and red indicate over- and under-representation of the corresponding class, respectively. The MapMan gene functional classification system consists of 34 major classes and their sub-classes . The major classes (e.g., RNA) and their sub-classes (e.g., regulation of transcription) are separated by a "period" in the figure. The z-values for the functional class over- or under-represented in each group are provided in Additional file 2.