Gene expression patterns of differentially expressed genes in SAM and the four stages of anther development (PMA, MA, SCP, TPA) categorized into 20 groups using the K-means clustering tool. Groups with similar expression patterns but different expression amplitudes have been grouped together to make 10 clusters. The normalized log transformed signal values were plotted for each of the five stages. The number of genes in the clusters is indicated along the side of the heatmap. The percentage of anther-specific genes in each cluster is specified at the lower left side of the heatmap.