Interaction between Arabidopsis thaliana and Sinorhizobium meliloti for improved plant growth and nitrogen nutrition

ARMIJO G; MEDINA M; KRAISER T; GRAS DE; ZUÑIGA A; GONZÁLEZ B; GUTIÉRREZ RA

Congreso; XII Reunión de Biología Vegetal Chile; 2017

Nitrogen (N) is an essentialmacronutrient whose availability in the soil has a critical role in plant growth  and  development in  natural  as well  as  in agricultural  environments.  Plants  acquire N directly from the soil and in somecases N can be provided by interacting with N-fixing  bacteria. This  type  of interactions  is  well described  in  legumes, but  are  also observed   in  some   non-legume   plant  species,   that   are  unable   to   form  nodules.Understanding   these   plant-bacteria   interaction  mechanisms   could   have  important agronomic implications,  reducing  the use  of  N-fertilizers in  non-legume  crops. Our  goal was to evaluate a functionalassociation between a non-legume model plant, Arabidopsis thaliana,  and a  N-fixing  model bacteria, Sinorhizobium  meliloti,  to study  and  identify molecular mechanisms underlying thisassociation. We found A. thaliana growth under N-limiting  conditions is  enhanced  by S. meliloti RMP110.  This enhancement  is in  part mediated by bacterial N-fixation.Dilution of 15N labeling when Arabidopsis plants were grown  with S. meliloti indicated  plants  indirectly acquired  atmospheric  N, where  14N  isotope predominates.  e  also determined  bacterial  root colonization  through  different types  of microscopy,  locating  the bacteria  in  the outer  layer  of the  root.  This was  also  corroborated by  an  endophytic assay  where  it was  shown  that  S.  meliloti is not  an intracellular  bacterium when  interacts  with Arabidopsis.  Finally,  we demonstrated that Arabidopsis homologs of key regulatory genes involvedin legume-rhizobium interactions are required for Arabidopsis growth promotionmediated by S. meliloti. Our results suggest a non-canonical  interaction  between A. thaliana and S.  meliloti RMP110,  without nodule formation,  or  intracellular colonization  of  the bacteria,  but  with conserved  molecular mechanisms  of legume-rhizobium interactions  for  improved growth  under  N-limiting conditions.