Exon skipping of AGAMOUS homolog PrseAG in developing double flowers of Prunus lannesiana (Rosaceae)

Two transcript isoforms of AGAMOUS homologs, from single and double flower Prunus lannesiana, respectively, showed different functions. The Arabidopsis floral homeotic C function gene AGAMOUS (AG) confers stamen and carpel identity. Loss of AG function results in homeotic conversions of stamens into petals and formation of double flowers. In order to present a molecular dissection of a double-flower cultivar in Prunus lannesiana (Rosaceae), we isolated and identified a single-copy gene, AG homolog from two genetically cognate P. lannesiana bearing single and double flowers, respectively. Sequence analysis revealed that the AG homolog, prseag-1, from double flowers showed a 170-bp exon skipping as compared to PrseAG (Prunus serrulata AGAMOUS) from the single flowers. Genomic DNA sequence revealed that abnormal splicing resulted in mutant prseag-1 protein with the C-terminal AG motifs I and II deletions. In addition, protein sequence alignment and phylogenetic analyses revealed that the PrseAG was grouped into the euAG lineage. A semi-quantitative PCR analysis showed that the expression of PrseAG was restricted to reproductive organs of stamens and carpels in single flowers of P. lannesiana 'speciosa', while the prseag-1 mRNA was highly transcribed throughout the petals, stamens, and carpels in double flowers from 'Albo-rosea'. The transgenic Arabidopsis containing 35S::PrseAG displayed extremely early flowering, bigger stamens and carpels and homeotic conversion of petals into staminoid organs, but ectopic expression of prseag-1 could not mimic the phenotypic ectopic expression of PrseAG in Arabidopsis. In general, this study provides evidences to show that double flower 'Albo-rosea' is a putative C functional ag mutant in P. lannesiana.