A potato Sus3 sucrose synthase gene contains a context-dependent 3' element and a leader intron with both positive and negative tissue-specific effects.

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Abstract
To examine which sequences are involved in regulating the potato sucrose synthase gene Sus3-65, we examined a series of deletion and substitution constructs in transgenic potato and tobacco plants. In a construct containing 3.9 kb of 59 flanking region, substitution of the native 39 sequence with the nopaline synthase 39 sequence and deletion of the leader intron did not significantly affect expression in vegetative tissues. However, in a construct containing only 320 bp of 59 flanking region, these changes had marked effects. Replacing the native 39 sequences with nopaline synthase 39 sequences caused a six- to 20-fold increase in expression in vascular tissue, and removing the leader intron almost completely abolished expression in potato plants. Surprisingly, removal of the leader intron from either the full-length construct or a construct containing only 320 bp of 59 flanking sequence reduced expression in vascular tissue of tobacco anthers at later stages of development but increased expression in pollen by more than 100-fold.