A new SBP-box gene BpSPL1 in silver birch (Betula pendula).

The SBP-box gene family represents a group of plant-specific genes encoding putative transcription factors. Thus far, SBP-domain protein binding sites have been found in the promoters of Arabidopsis APETALA1 and Antirrhinum SQUAMOSA. A putative SBP-domain binding element has been observed in the promoter of BpMADS5, a close homologue of Arabidopsis FRUITFULL in silver birch (Betula pendula). A novel SBP-box gene from birch named BpSPL1 has been cloned and characterized. The nucleotide sequence of BpSPL1 is similar to Antirrhinum SBP2 and Arabidopsis SPL3, apart from the unique finding that BpSPL1 does not contain an intron typical to all other known SBP-box genes studied thus far. According to Northern blot analysis, BpSPL1 is expressed in birch inflorescences as well as in shoots and leaves. Studies using electrophoretic mobility shift assay demonstrate that there are nuclear proteins in birch inflorescences which specifically bind to the SBP binding element of the promoter of BpMADS5. BpSPL1 expressed in Escherichia coli also specifically binds to this element. According to Southern blot analysis, there are at least two SBP-box genes in birch. The results suggest that SBP-box genes are involved in the regulation of flower development in birch.