REG-promoter clustering. For each Arabidopsis promoter, number of each octamer REG within a region from -400 to -40 bp was scored, and subjected to 2D hierarchical clustering. The vertical axis shows promoters and the horizontal axis does REGs. The matrix means number of REG sequences. Two small promoter clusters are shown in the figure together with the whole REGs. (A) A part of promoter cluster rich in GCCCA motif for meristematic expression. Ribosomal proteins are shown in blue. (B) A part of promoter cluster rich in ACGT motif for environmental response. Promoter names are expressed in color according to expression data from AtGenExpress. Red: abiotic stress-positive, orange: abiotic stress-negative, green: light-positive, black: no response to abiotic stress or light, grey: no expression data found. (C) An example of clustered REGs. A part of the ACGT cluster shown in the top of Panel A is enlarged. ACGT in the octamers are highlighted with orange.