Nitrogen-fixing root nodules elicited by rhizobial potassium ion transporter Smkup1: senescence and autophagy

With the aim to elucidate the interdependence between potassium transport by the host plant in nodule cells and potassium transport in bacteroids, a null mutant of rhizobial potassium ion transporter Smkup1 was created and investigated. The mutation, according to cytological analysis, has not caused specific aberrations in the root nodules’ anatomy and ultrastructure, but a significant induction of the expression of host plant and rhizobial genes involved in the stress response was observed. At the same time, an opposite trend was observed for genes of the autophagy pathway that have shown a significant downregulation of expression. To identify the mechanisms of interplay between autophagy and senescence in the root nodule, an in silico analysis of protein–protein interactions of positive (Beclin 1) and negative (NAC1, BAK1) regulators of autophagy was performed. The resulting networks allowed the predictions of interacting proteins putatively linking symbiotic interactions, autophagy, stress, programmed cell death (PCD), and senescence. Based on these data, we hypothesized that modulation of the expression of these genes in the root nodule could be the way to extend the root nodule’s lifespan and the duration of the nitrogen fixation process.