Infection and nodulation of Discaria trinervis roots expressing an autoactive form of CCamK

BRITO DEVOTO T; IMANISHI L; GHERBI H; SVISTOONOFF S; WALL LG

Montpellier

Congreso; 18 th International Meeting on Frankia and Actinorhizal Plants; 2015

IRD

Discaria trinervis is a patagonic shrub belonging to the Rhamnaceae family of the Rosales order, which has the ability to associate with the actinobacteria Frankia. In contrast to model legumes and actinorhizal Fagales, D. trinervis roots are infected through the intercellular infection pathway that does not involve root hairs or infection threads. We have recently shown that a Calcium and calmodulin-dependent protein kinase (CCamK) is involved in Discaria trinervis nodulation. Like in other actinorhizal plants and legumes, the expression of a truncated version of a CCamK gene lacking the auto-inhibitory/CaM domain (=CCamK*) induces the formation of nodules without the presence of Frankia (1). To further analyze the prenotype of plants expressing CCamk*, we generated transgenic roots containing also a ProDt12:GFP fusion which is a specific marker of plant cell infection by Frankia (Imanishi et al, unpublished results). Our results show that CCamK expression leads to an increased number of nodules per root but also an increased proportion of empty nodules and had no effect on overall biomass. Close examination of nodules expressing CCaMK* and GFP showed the presence of expanded intercellular areas full of Frankia which are reminiscent of infection pockets. Those structures were absent in control nodules expressing Dt12:GFP alone. This finding suggests that CCamK not only in triggers nodule formation in D. trinervis but also plays a role during Frankia infection.