Actinorhizal plant defence-related genes in response to symbiotic Frankia

Actinorhizal plants have become increasingly important as climate changes threaten to remake the global landscape over the next decades. These plants are able to grow in nutrient-poor and disturbed soils, and are important elements in plant communities worldwide. Besides that, most actinorhizal plants are capable of high rates of nitrogen fixation due to their capacity to establish root nodule symbiosis with N2-fixing Frankia strains. Nodulation is a developmental process that requires a sequence of highly coordinated events. One of these mechanisms is the induction of defence-related events, whose precise role in a symbiotic interaction remains to be elucidated. This review summarises what is known about the induction of actinorhizal defence-related genes in response to symbiotic Frankia and their putative function during symbiosis.