SOYBEAN (LBC3), PARASPONIA, AND TREMA HEMOGLOBIN GENE PROMOTERS RETAIN SYMBIOTIC AND NONSYMBIOTIC SPECIFICITY IN TRANSGENIC CASUARINACEAE -IMPLICATIONS FOR HEMOGLOBIN GENE EVOLUTION AND ROOT-NODULE SYMBIOSES

The purpose of this study was to compare the control of expression of legume and nonlegume hemoglobin genes. We used the Casuarina glauca an d Allocasuarina verticillata transformation system to examine the prop erties of the soybean (lbc3), Parasponia andersonii, and Trema tomento sa hemoglobin gene promoters in actinorhizal plants. Expression of the hemoglobin promoters gus genes was examined by fluorometric and histo chemical assays. The fluorometric assays in various organs showed that the soybean and P. andersonii promoters were most active in nodules w hereas the T. tomentosa promoter gave a very high activity in roots, T he histochemical study showed that GUS activity directed by the soybea n and the I! andersonii gus chimeric genes appeared mainly confined to the infected cells of the C. glauca and A. verticillata nodules, The T. tomentosa hemoglobin promoter was primarily expressed in the root's cortex and vascular tissue. The results indicate that the soybean, It andersonii, and T, tomentosa hemoglobin promoters retain their cell-s pecific expression in transgenic members of the Casuarinaceae, suggest ing a close relationship between legume, Ulmaceae member, and actinorh izal hemoglobin genes. The conservation of the mechanism for nodule-sp ecific expression of soybean, P, andersonii and C,glauca and A. vertic illata hemoglobin genes is discussed in view of recent molecular phylo genetic data that suggest a single origin for the predisposition to fo rm root nodule symbioses.