Two glutamine synthetase genes from Phaseolus vulgaris L. display contrasting developmental and spatial patterns of expression in transgenic Lotus corniculatus plants.

Abstract

The gln-.gamma. gene, which specifies the .gamma. subunit of glutamine synthetase in Phaseolus vulgaris L., has been isolated and the regulatory properties of its promoter region analyzed in transgenic Lotus corniculatus plants. A 2-kolobase fragment form the 5''-flanking region of gln-.gamma. conferred a strongly nodule-enhanced patter of expression on the .beta.-glucuronidase reporter gene. Parallel studies on the promoter of another glutamine synthetase gene (gln-.beta.) showed that a 1.7-kilobase fragment directed 20-fold to 140-fold higher levels of .beta.-glucuronidase expression in roots than in shoots. Histochemical localization of .beta.-glucoronidase activity in nodules of the transgenic plants indicated that the chimeric gln-.gamma. gene was expressed specifically in the rhizobially infected cells; expression of the gln-.beta. construct was detected in both cortical and infected regions of young nodules, and became restricted to the vasular tissue as the nodule matured. We conclude that gln-.beta. and gln-.gamma. genes are differentially expressed both temporally spatially in plant development and that the cis-acting regulatory elements responsible for conferring these contrasting expression patterns are located within a 2-kilobase region upstream of their coding sequences.