To investigate genetic mechanisms acting on multigene family in plants, we analyzed sequence variation in the
rbcS gene of 13 species of Triticeae and one species each of related tribes (Bromeae and Aveneae). A total of 36
rbcS genes were analyzed. Based on dimorphism in the length of intron, the
rbcSs of investigated species were classified into two subfamilies A and B. The difference in intron length was caused by an indel of about 200 bp in the middle of the intron. The two subfamilies of
rbcS were present in the three tribes, indicating that the divergence of
rbcS subfamilies occurred before the split of these tribes. Generally, variation between the two subfamilies of
rbcS was larger than that within subfamily, but these two measures were about the same at the tribe level. This result suggested that divergence of the subfamilies of
rbcS occurred at about the same time of tribe diversification. The level of nucleotide variation in the exon region between subfamilies was reduced in the Triticeae, but clear change was not detected in the intron sequence. This result suggested that the exon sequences between subfamilies of
rbcS were homogenized without affecting the intron sequence in the Triticeae lineage.
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