Exon/Intron structural organization of plant Sus genes. (A) Exon/intron structures of the seven sucrose synthase genes, GaSus1 to 7, from diploid fiber cotton (G. Arboreum, A2). Black boxes denote exons within coding regions, and the lines connecting them represent introns. Numbers in boxes or above lines represent the sizes (bp) of corresponding exons or introns, respectively. The 5' and 3' untranslated regions (UTRs) are represented by blank boxes. For highlighting the conservation of exon structures, the sizes of exons, introns and non-coding UTRs are not actually presented. (B) Exon/intron structures of the sucrose synthase genes, AtSus1-6 and OsSus1-6, from Arabidopsis and rice, respectively.