Minimal enhancer elements of the leghemoglobinlba andlbc3 gene promoters fromGlycine max L. have different properties

The characteristics of the soybean leghemoglobinlba gene promoter were analyzed and important promoter elements from thelba andlbc3 promoters were compared using transgenicLotus corniculatus plants. A 5′ deletion analysis of thelba promoter delimited twocis-acting elements controlling expression: a distal positive element (−1254, −884) required for expression and a proximal element (−285, −60) essential for full-level activity. In contrast to the corresponding region of thelbc3 promoter, thelba proximal element is unable to control expression from the heterologous CaMV 35S enhancer. The upstream positive element of thelba gene contains a position- and orientation-independent enhancer between positions (−1091, −788). The sequence of this enhancer region is conserved in thelbc3 gene upstream (−1333, −1132) of the previously assigned strong positive element (SPE; −1090, −947). The present analysis revealed some of the properties of this extendedlbc3 SPE element. The extended element (−1364, −947) functions in both orientations from 5′ locations whereas the SPE2 subcomponent (−1364, −1154) containing the conserved sequence is only active in the correct orientation. Removal of the SPE2 by internal deletion demonstrates that the SPE2 subcomponent is indispensable for the activity of thelbc3 upstream positive element. These results indicate that the upstream positive elements of thelba andlbc3 genes possess different properties although their conserved minimal enhancer sequence has similar function. This may reflect the differential expression of the twolb genes ofGlycine max L.