Sequence variability of nine cytosolic ascorbate peroxidases in polyploid strawberry

Little is known about differential gene expression at the molecular level in polyploid plants. Here, we describe the molecular analysis of ApxSC (cytosolic ascorbate peroxidase from a polyploid strawberry) genes. Fifty-three cDNAs encoding ApxSC were isolated from a strawberry fruit cDNA library. These clones were categorized (i) into nine homologous (95 to 99%) gene groups on the basis of their nucleotide sequences and (ii) into four groups of similar (> 98%) polypeptides on the basis of their deduced amino acid sequences. Sequence variation among the gene groups was dispersed throughout the gene, while differences among the polypeptide groups were observed only at three amino acid positions (9, 63, and 233). These results imply that the ApxSC genes show co-dominant expression resulting from multiple alleles. This hypothesis is supported by genomic blots and primer extension analyses.