Diffusible factor(s) from Frankia BCU110501 modifies nodulation kinetics in Discaria trinervis, an intercellular root infected actinorhizal symbiosis

GABBARINI L; WALL LG

FUNCTIONAL PLANT BIOLOGY

CSIRO PUBLISHING

Año: 2011 vol. 38 p. 662 - 670

1445-4408

Nodulation kinetics was analyzed in two different nitrogen fixing actinorhizal symbioses that show different pathways for infection: Alnus acuminata, which is infected by Frankia ArI3 via deformed root hairs, and Discaria trinervis, which is infected by Frankia BCU110501 via intercellular invasion. Both symbiotic pairs are non-compatible in cross-inoculation experiments. The dose – response effects in nodulation were studied in Alnus acuminata seedlings using different concentrations of compatible and non-compatible bacteria in co-inoculation experiments. RFLP-PCR analysis of DNA extracted from nodule vesicles, and plant-trapping analysis with crushed nodules as inoculum showed that there was no co-occupation in Alnus acuminata nodules when plants were co-inoculated with Frankia BCU110501 and Frankia ArI3. Despite the lack of co-occupation, the non-infective Frankia BCU110501 could modify the nodulation parameters t0, tNOD, v0 and vR of non-host plant Alnus acuminata when the infective strain Frankia ArI3 was also present in the inoculum. The results suggest that although Frankia BCU110501 was not able to induce nodulation in Alnus acuminata, its interaction with the plant could induce autoregulation in the plant as if some kind or level of infection or partial recognition could be achieved. We explored the possibility of physiological complementation of the heterologous Frankia BCU110501 for nodulation of Alnus acuminata by the availability of diffusible factors originated in the homologous Frankia ArI3 in the presence of compatible root exudates. Despite the possibility of full activation between bacteria and host-plant there was no co-infection of Frankia BCU110501 in Alnus or of Frankia ArI3 in Discaria either. These negative results suggest the existence of a physical recognition barrier in actinorhizal symbiosis that operates after early interactions, involving something other than root exudates and diffusible factors of bacterial or plant origin, regardless of the type of infection pathway developed in the symbiosis.