Specialised protein secretion in plant-microbe symbioses
D. WANG (1), O. Oztas (2), H. Pan (2), M. Kim (2), C. Stonoha (2), X. Wu (3), B. Wang (3) (1) University of Massachusetts, Amherst, U.S.A.; (2) University of Massachusetts, U.S.A.; (3) Nanjing University, China

Legumes can engage rhizobia, transforming free-living bacteria into nitrogen-fixing organelles (symbiosomes). This symbiosis co-opts the machinery of a more widespread association with arbuscular mycorrhizal (AM) fungi1. Both symbionts are outlined by a specialized interfacial membrane, which is derived from the host plasma membrane but maintains its unique identity. The protein secretory pathway has been co-opted to deliver host factors to the microsymbiont2,3. We recently discovered that the fidelity of this symbiosis-specific protein secretion is insured by a t-SNARE protein generated by a transcriptional regulatory mechanism called alternative cleavage and polyadenylation, and that this symbiotic t-SNARE is crucial to a properly developed symbiosis4. Unlike AM fungi, rhizobia exist intracellularly through a persistent infection. Sustaining and controlling such a chronic infection is a major challenge to the host, and could be a key factor in the emergence of the nitrogen-fixing symbiosis. We discovered that to insure the survival of newly internalized rhizobia, the host processes certain symbiosome membrane proteins to suppress excessive defence responses. As bacteroids mature, a new set of factors is needed to maintain the viability of such enlarged bacteria. We discovered that one of the Nodule-specific Cysteine-Rich (NCR) peptides is required for the survival of differentiated bacteroids5. Current evidence suggests this NCR peptide localizes to the bacterial surface, and could promote bacteroid survival by facilitating metabolite exchange between the host and the bacteria.


Abstract Number: P4-1
Session Type: Plenary