THE 22 BP W1 ELEMENT IN THE PEA LECTIN PROMOTER IS NECESSARY AND, AS A MULTIMER, SUFFICIENT FOR HIGH GENE-EXPRESSION IN TOBACCO SEEDS

The pea lectin (Psl) gene encodes an abundant seed protein. Its seed-s pecific expression pattern is conserved in transgenic tobacco plants. Progressive 5' promoter deletions resulted in a gradual decrease of tr anscriptional activity in tobacco seed. A fragment of 115 bp still con ferred seed-specific expression albeit at a low level. This fragment c ontains a 22 bp element (W1), which has been demonstrated to be import ant for seed-specific expression when coupled as a trimer to a heterol ogous TATA box (de Pater ct al., Plant Cell 5: 877-886, 1993). Here we show that deletion of WI in the natural promoter context resulted in a strongly decreased level of gene expression. A 4 bp mutation of WI r educed the expression of truncated derivatives of the Psl promoter. A single copy of WI coupled to the TATA box of the CaMV 35S promoter dir ected low gene expression in seeds and leaves. Multimerization enhance d the expression in seeds up to 100-fold, to levels found with the Psl promoter, whereas the expression level in leaves remained low. These results demonstrate that the W1 element is an essential control elemen t in the Psl promoter. When taken out of its natural context and multi merized, it is sufficient for high expression in seeds.