Molecular cloning, characterization and expression of WAG-2 alternative splicing transcripts in developing spikes of Aegilops tauschii

WAG-2 is a C-class MADS-box gene, which is orthologous to AGAMOUS (AG) in Arabidopsis. The AG group C-class MADS-box genes are involved in stamen and pistil identity. In this study, two WAG-2 transcripts, namely, WAG-2f and WAG-2g, were isolated and characterized from Aegilops tauschii. The open reading frames of WAG-2f and WAG-2g were 825 and 822 bp, respectively, encoding 275 and 274 amino acid residues. BLAST searches of partial WAG-2 genomic sequence against the draft sequence of Ae. tauschii genome database revealed the complex structure of WAG-2 gene, which consisted of seven exons and six introns. The WAG-2f and WAG-2g cDNAs were two alternative splicing transcripts. The alternative splicing events were produced by an alternative 5' splice site. The expression level of WAG-2f transcript, which was extremely weak in young spikes of floret primordium formation stage, increased as the spikes developed. The highest expression was observed in the spikes at the anther separation stage. Low expression levels of WAG-2f were also detected at the tetrad stage. The WAG-2g transcript was expressed at all four stages of spike development but at a relatively low level. The expression pattern of the two transcripts was distinctly different during floral development, thereby suggesting a functional divergence.