Study of early interactions and recognition phenomena in actinorhizal symbioses with different infection pathways

GABBARINI L; WALL LG

Bariloche, Argentina

Congreso; 15th International Frankia and Actinorhizal Plants Meeting; 2008

The nitrogen fixing nodules induced by Frankia in Discaria trinervis roots are an example of intercellular root invasion pathway (Valverde and Wall 1999) that implies no root hair deformation at all during recognition and infection, clearly different to the intracellular infection pathway via root hair (Wall and Berry 2008).  The induction of root nodule development in actinorhizal symbiosis would depend on the concentration of factors produced by the bacteria and the plant. A detailed analysis of nodulation descriptors parameters revealed different factors related to the nodulation process in A. acuminata and D. trinervis. The initial time for nodulation (t0), the initial nodulation rate (v0), and the total time of nodule development (tNOD) (Gabbarini and Wall 2008), were quantified in different experimental conditions: co-inoculation of Alnus acuminata with increasing concentrations of non-infective Frankia BCU110501 together with the full compatible infective Frankia ArI3 (the indicator strain) used at a limiting concentration; or putting to growth D. trinervis and A. acuminate in the same device (pouche) and inoculating with: i- BCU110501; ii- ArI3; and iii- ArI3 + BCU110501. All the above nodulation parameters were modified by changing doses of full compatibility infective strain Frankia BCU110501 in D. trinervis, but just tNOD and v0 were modified by changing doses of full compatibility strain Frankia ArI3 in A. acuminata; v0 appears to be an expression of symbiotic recognition between partners since only fully symbiotic indicator Frankia was able to change it; t0 seems not to reflect symbiotic recognition because it can also be modified by non infective Frankia but suggest the existence of a basic level of plant microbe recognition. t0, reflecting the time required for the early interactions towards nodulation, is an inverse measure of the ability to establish early interactions towards nodulation.  The presence of a par symbiotic complete generate a factor/s able to act in trans over the other par symbiotic  reducing t0 values suggesting that a plant-bacteria match specific factor is involved and favors very early interactions. The occupancy of nodules from D. trinervis plant and A. acuminata co-inoculated with Frankiaes isolates BCU110501 and ArI3 were analyzed by plant trapping and RFLP-PCR. Both methods showed the presence of single Frankia BCU110501 in nodules from D. trinervis and single Frankia ArI3 in nodules from A. acuminata.