Analysis of the Expression Pattern Conferred by the PsEnod12B Promoter from the Early Nodulin Gene of Pisum sativum in Transgenic Actinorhizal Trees of the Casuarinaceae Family

Abstract

To investigate the similarities between nitrogen-fixing symbioses in Rhizobium-legumes and Frankia-actinorhizal plants, we studied the gus expression pattern conferred by the early nodulin promoter PsEnod12B from Pisum sativum in two transgenic Casuarinaceae trees, Allocasuarina verticillata and Casuarina glauca. Respectively 6 and 13 transgenic lines of C. glauca and A. verticillata were obtained following genetic transformation with the disarmed strain of Agrobacterium tumefaciens C58C1 (pGV2260; pBIN-PsEnod12B-gus). In non-symbiotic tissues, the gus gene was expressed exclusively in the vascular system of the aerial parts of the plants. In mature nodules, PsEnod12B drove some gus expression in large Frankia-infected cortical cells. This specificity was different from that observed in pea nodules where PsEnod12B was found expressed in the infection zone. No reporter gene activity was visible at the early stages of the symbiotic process with Frankia, including infected root hairs and prenodules. Whereas some transcription factors of Allocasuarina and Casuarina are able to interact with the PsEnod12B promoter, the pattern of expression is modified in nodules of these non-legume heterologous hosts.