Identification and functional characterization of genes induced by seed exudates in Azorhizobium caulinodans ORS571

Abstract:

Abstract: [Objective] To identify genes induced by plant seed exudates in Azorhizobium caulinodans ORS571. [Methods] Using promoterless kanamycin resistance gene (Kmr) on transposon as reporter gene and seed exudates as inducers, we screened genes of interest from transposon insertion mutants libraries. We streaked mutants on TY solid medium with Km, and another with Km and seed exudates correspondingly. If Kmr is inserted into a gene that can be induced by plant signals, Kmr will possibly express at the same time. Thus, mutants were selected that can grow on medium with Km and exudates, rather than on medium with Km. [Results] We identified a lysE family gene named asiE in strain Azc0 that can be induced by seed exudates and further analysis indicated that the inducing substance is canavanine(CAN). lacZ transcriptional fusion of asiE confirmed that its expression increased by ten-fold or so under the induction of CAN. Besides, lysE gene in four different species of Rhizobia can be induced by CAN. lysE mutants are all sensitive to CAN treatment whereas wild type are resistant. [Conclusion] The existence of LysE can make rhizobia better survived in the rhizosphere and may play an important role in early stage of interaction between rhizobia and host plant.