JXB Advance Access originally published online on October 16, 2003
Journal of Experimental Botany, Vol. 54, No. 393, pp. 2655-2660,
December 1, 2003
© 2003 Oxford University Press
Mutation in the ap2-6 allele causes recognition of a cryptic splice site
Received 8 May 2003; Accepted 6 August 2003
Department of Biology, University of Western Ontario, 1151 Richmond Street North, London, Ontario N6A 5B7, Canada
* To whom correspondence should be addressed. Fax: +1 519 661 3935. E-mail: skohalmi{at}uwo.ca
Mutations in the homeotic gene APETALA2 of Arabidopsis thaliana cause severe developmental alterations, most prominently homeotic floral organ replacements from petals to carpels and petals to stamens in the outer two floral whorls. To date, ten different alleles have been identified conferring phenotypes of various degrees. Of these ten alleles, only three have been characterized at the sequence level. The identification of the sequence alteration in the ap2-6 allele is reported here. In ap2-6 a single G·C to A·T transition occurred at the 3' end of intron 6 (position 1342) which leads to a dinucleotide loss at the mRNA level. This change is consistent with the G·C to A·T transition destroying a conserved dinucleotide motif (AG) required for proper splice recognition and with the resulting recognition of the next available downstream AG dinucleotide which in AP2 is immediately adjacent to the authentic 3' splice site. The dinucleotide loss will cause a frameshift, the translation of three incorrect amino acids and a premature stop codon resulting in a truncation of the AP2 sequence within the AP2-R2 domain. Such a truncation is predicted to impact severely on the function of AP2 and is consistent with the observed phenotype.
Key words: ap2 mutant allele, ap2-6, APETALA2, Arabidopsis, developmental mutant, homeotic mutant, splicing.