Kb. Ramlov et al., SITE-DIRECTED MUTAGENESIS OF THE ORGAN-SPECIFIC ELEMENT IN THE SOYBEAN LEGHEMOGLOBIN IBC3 GENE PROMOTER, Plant journal, 4(3), 1993, pp. 577-580
The expression of a soybean leghemoglobin 5'lbc3-GUS-3'nos chimeric ge
ne was analyzed in Lotus corniculatus after site-specific mutagenesis
of the nodulin consensus sequences, AAAGAT and CTCTT, present in the o
rgan-specific element (OSE) (-139 to -102). Full-length promoters (-19
56,+46) carrying clustered point mutations in the CTCTT sequence or in
both the AAAGAT and the CTCTT sequences were inactive. Point mutation
s in the AAAGAT sequence had only minor effects on the expression leve
l. Substitution of the ATTG sequence between the AAAGAT and the CTCTT
sequences in the OSE reduced the activity in nodules to 10%. This, tog
ether with the conservation of the ATTGT sequence in the same position
of leg-hemoglobin genes from other legumes, indicates that these sequ
ences, in addition to the nodulin consensus sequences of the OSE, are
important for high-level nodule-specific expression. Substitution of t
he CTCTT sequences outside the OSE (-44, -40 and -79, -75) results in
promoter activities of approximately 50%.