Primer pairs were designed to amplify the genomic DNA sequence of the alpha-farnesene synthase (AFS) gene by PCR.The PCR products were sequenced,spliced and compared to Cdna sequences in the GenBank (accession No.AY182241).The genomic sequence and intron-exon organization of the AFS gene were thus obtained.The AFS genomic sequence has been registered in the GenBank (accession No.DQ901739).It has 6 introns and 7 exons,encoding a protein of 576 amino acids.The sizes of the 6 introns were 108 bp,113 bp,＞1000 bp,125 bp,220 bp and 88 bp,and their phases were 0,1,2,2,0,0,respectively.The sizes of the deduced amino acids of the 7 exons were 57,89,127,73,48,83 and 99,respectively.The AFS protein contained three motifs:the RR(X8)W motif encoded by a sequence in exon 1,and the RxR motif and DDxxD motif encoded by two sequences in exon 4.After comparing the AFS genomic sequence (accession No.DQ901739) to the Cdna sequence (accession No.AY523409) in the GenBank,it was found that there were 6 single-nucleotide polymorphisms between the two sequences,four of which caused mutations at the amino acid level.Interestingly,one amino acid mutation (291R→G) was found in the RxR motif,and further investigation is needed to determine whether the alpha-farnesene synthesis ability and superficial scald susceptibility of apples are influenced by this amino acid mutation and other mutations.
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