An allele of the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene (Md-ACS1), the transcript and translated product of which have been identified in ripening apples (Malus domestica), was isolated from a genomic library of the apple cultivar, Golden Delicious. The predicted coding region of this allele (ACS1-2) showed that seven nucleotide substitutions in the corresponding region of ACS1-1 resulted in just one amino acid transition. A 162-bp sequence characterized as a short interspersed repetitive element retrotransposon was inserted in the 5 -flanking region of ACS1-2 corresponding to position ؊781 in ACS1-1. The XhoI site located near the 3 end of the predicted coding region of ACS1-2 was absent from the reverse transcriptase-polymerase chain reaction product, revealing that exclusive transcription from ACS1-1 occurs during ripening of cv Golden Delicious fruit. DNA gel-blot and polymerase chain reaction analyses of genomic DNAs showed clearly that apple cultivars were either heterozygous for ACS1-1 and ACS1-2 or homozygous for each type. RNA gel-blot analysis of the ACS1-2 homozygous Fuji apple, which produces little ethylene and has a long storage life, demonstrated that the level of transcription from ACS1-2 during the ripening stage was very low.

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Seed coat color in soybeans is determined by the I ( Inhibitor ) locus. The dominant I allele inhibits seed coat pigmentation, and it has been suggested that there is a correlation between the inhibition of pigmentation by the I allele and chalcone synthase ( CHS ) gene silencing in the seed coat. Analysis of spontaneous mutations from I to i has shown that these mutations are closely related to the deletion of one of the CHS genes (designated ICHS1 ). In soybeans with the I/I genotype (cv. Miyagi shirome), a truncated form of the CHS gene ( CHS3 ) is located in an inverse orientation 680 bp upstream of ICHS1 , and it was previously suggested that the truncated CHS3-ICHS1 cluster might be involved in CHS gene silencing in the seed coat. In the current study, the truncated CHS3-ICHS1 cluster was compared with the corresponding region of pigmented seed coat mutants in which I had changed to i in Miyagi shirome and in the strain Karikei 584. In the Karikei 584 mutant, the truncated CHS3-ICHS1 cluster was retained and the sequence diverged at a point immediately upstream (32 bp) of this cluster. The sequences upstream of the points of divergence in both mutants almost perfectly matched a part of the registered sequence in a soybean BAC clone containing the soybean cyst nematode resistance-associated gene, and inspection of the sequences suggested that the sequence divergence of the CHS gene in the Karikei 584 and Miyagi shirome mutants was due to an unequal crossing-over via 4-bp or 5-bp short repeats, respectively.

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