NPR1 protein regulates pathogenic and symbiotic interactions between Rhizobium and legumes and non-legumes.
BACKGROUND
Legumes are unique in their ability to establish symbiotic interaction with rhizobacteria from Rhizobium genus, which provide them with available nitrogen. Nodulation factors (NFs) produced by Rhizobium initiate legume root hair deformation and curling that entrap the bacteria, and allow it to grow inside the plant. In contrast, legumes and non-legumes activate defense responses when inoculated with pathogenic bacteria. One major defense pathway is mediated by salicylic acid (SA). SA is sensed and transduced to downstream defense components by a redox-regulated protein called NPR1.


RESULTS
We used Arabidopsis mutants in SA defense pathway to test the role of NPR1 in symbiotic interactions. Inoculation of Sinorhizobium meliloti or purified NF on Medicago truncatula or nim1/npr1 A. thaliana mutants induced root hair deformation and transcription of early and late nodulins. Application of S. meliloti or NF on M. truncatula or A. thaliana roots also induced a strong oxidative burst that lasted much longer than in plants inoculated with pathogenic or mutualistic bacteria. Transient overexpression of NPR1 in M. truncatula suppressed root hair curling, while inhibition of NPR1 expression by RNAi accelerated curling.


CONCLUSIONS
We show that, while NPR1 has a positive effect on pathogen resistance, it has a negative effect on symbiotic interactions, by inhibiting root hair deformation and nodulin expression. Our results also show that basic plant responses to Rhizobium inoculation are conserved in legumes and non-legumes.
Peleg-Grossman
Smadar
S
Department of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
Golani
Yael
Y
Kaye
Yuval
Y
Melamed-Book
Naomi
N
Levine
Alex
A
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000382:microbiology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D046913:Medicago truncatula / Q000187:drug effects / Q000235:genetics / Q000382:microbiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000382:microbiology; D016958:Pseudomonas putida / Q000187:drug effects / Q000502:physiology; D044224:Pseudomonas syringae / Q000187:drug effects / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020156:Salicylic Acid / Q000494:pharmacology; D012689:Sequence Homology, Nucleic Acid; D016962:Sinorhizobium meliloti / Q000187:drug effects / Q000502:physiology*; D013559:Symbiosis / Q000187:drug effects
D008565:Membrane Proteins; D009861:Onium Compounds; D010940:Plant Proteins; D017382:Reactive Oxygen Species; C045625:nodulin; C007517:diphenyleneiodonium; D020156:Salicylic Acid