Nitrogen-fixing root nodules elicited by rhizobial potassium ion transporter Smkup1under suboptimal potassium supply: senescence and autophagy

Maria G. Semenova¹Teodoro Coba De La Peña²Aleksandra N. Petina¹Tatiana Ivashina³Elena Erika Fedorova^1*

• ¹Institute of Plant Physiology, Russian Academy of Sciences (RAS), Moscow, Russia
• ²Centro de Estudios Avanzados en Zonas Aridas, La Serena, Chile
• ³3Skryabin Institute of Biochemistry and Physiology of Microorganisms, Federal Research Center Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, 142290 Russia,, Federal'nyj issledovatel'skij centr Pusinskij naucnyj centr biologiceskih issledovanij Rossijskoj Akademii nauk, Pushchino, Russia

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 induced significant induction of the expression of host plant and rhizobial genes involved in the stress response. An opposite trend was observed for genes of the autophagy pathway showing 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 root nodule could be the way to extend the root nodule lifespan and the duration of nitrogen fixation process.