Table 1.

Summary of proteomic studies focused on the legume-Rhizobium symbiosis.

Legume sp.	Rhizobium sp.	References	Main outcome
I. STUDIES FOCUSED ON THE PLANT PARTNER
G. max roots (wt and SS2-2 mutant)	B. japonicum USDA110	Lim et al., 2010	Protein-mediated suppression of defense-related responses in root cells upon inoculation with symbiotic bacteria.
G. max root hairs	B. japonicum USDA110	Wan et al., 2005	Induction of phospholipases, phosphoglucomutases, lectins, and an actin isoform in soybean roots upon B. japonicum inoculation.
G. max nodules (cytosol fraction)	B. japonicum USDA110	Oehrle et al., 2008	Proteins related to carbon and nitrogen metabolism, oxygen supply and protection are predominantly found in the cytosol of nodule cells.
G. max En-b0-1 roots (supernodulating)	B. japonicum MAFF 211342	Salavati et al., 2012	Identification of a correlation between the levels of a peroxidase isoform and nodulation at the protein but not transcript level in soybean nodules.
L. japonicus roots and nodules	M. loti MAFF30309	Dam et al., 2014	Establishment of 2D-PAGE reference maps of L. japonicum roots and nodules.
M. alba nodules	S. meliloti 1021	Natera et al., 2000	Identification of nearly 100 plant and bacterial proteins in white sweetclover nodules.
M. truncatula roots	S. meliloti 2011	Bestel-Corre et al., 2002	Two leghemoglobin isoforms and one enolase protein were accumulated in roots upon inoculation with symbiotic bacteria.
M. truncatula nodules	S. meliloti 2011	Larrainzar et al., 2007	Identification of 377 plant proteins in nodules, mostly related to amino acid metabolism and protein synthesis and degradation.
M. truncatula nodules	S. meliloti 2011	Larrainzar et al., 2009	Integrative proteomic and metabolomic analysis of the effects of drought stress in the plant and bacteroid fractions of M. truncatula nodules.
M. truncatula roots and nodules	S. meliloti 2011	Larrainzar et al., 2014	Absolute quantification proteomics and gene expression analyses show that sulfur metabolism and ethylene biosynthesis have key roles in the response of nodules and roots subjected to drought stress.
M. truncatula shoots and roots	S. meliloti 1021	Molesini et al., 2014	Analysis of local and systemic responses of M. truncatula roots and shoots upon inoculation.
M. truncatula roots (wt and skl mutant)	S. meliloti 1021	Prayitno et al., 2006	Increased abundance of one ACC oxidase isoform in wild-type roots but not in roots of the supernodulating skl mutant upon inoculation.
M. truncatula roots and shoots	S. meliloti 2011	Staudinger et al., 2012	Detection of salt and drought stress markers and identification of an improved plant response to stress of plants grown under symbiotic conditions when compared to nitrate-fed plants.
M. truncatula shoots	S. medicae WSM419 and S. meliloti 2011	Staudinger et al., 2016	Plants grown under symbiotic conditions present reduced levels of leaf senescence during drought stress independently of the efficiency of the symbiotic Rhizobium strain used.
P. sativum shoots	R. leguminosarum bv. viciae	Irar et al., 2014	Identification of variations in protein abundance as part as the local responses of pea nodules grown under split-root conditions and subjected to water stress.
P. sativum shoots (soluble and plasma membrane fractions)	R. leguminosarum bv. viciae	Desalegn et al., 2016	Indications of a positive influence of the symbiotic interaction on the activation of the plant defense responses upon pathogen attack.
P. sativum shoots	R. leguminosarum bv. viciae	Turetschek et al., 2016	Proteomic and metabolomic analyses of two pea cultivars with varying pathogen resistance levels associate tolerance to ethylene biosynthesis and suppression of cell death responses.
V. unguiculata roots	Rhizobium sp. NGR234	Krause and Broughton, 1992	One of the first proteomic studies analyzing symbiosis-specific proteins potentially involved in root-hair deformation in cowpea.
II. STUDIES FOCUSED ON THE Rhizobium PARTNER
B. japonicum USDA110	Bacteroids	Sarma and Emerich, 2005	Abundance of proteins related to nitrogen and carbon metabolism, and transport in soybean nodule bacteroids.
B. japonicum USDA110	Free-living cells vs. bacteroids	Sarma and Emerich, 2006	Compared to bacteria under free-living conditions, nodule bacteroids present unusually low levels in proteins related to fatty acid and nucleic acid metabolism.
B. japonicum USDA110	Bacteroids	Delmotte et al., 2010	In contrast to previous reports, application of more sensitive LC-MS/MS-based approaches identifies a complete set of proteins related to de novo nucleoside and nucleotide biosynthesis in bacteroids.
Bradyrhizobium sp. ORS278	Bacteroids (Aeschynomene indica root and stem nodules)	Delmotte et al., 2014	Root and stem nodule bacteroids show expression of similar sets of proteins, mostly related to central metabolism. As exceptions, proteins involved in photosynthesis were exclusive found in stem nodules.
M. loti MAFF30309	Free-living cells vs. bacteroids	Tatsukami et al., 2013	Differentiated bacteroids do not longer express proteins either involved in peptidoglycan biosynthesis or proteins related to the flagellum.
M. loti MAFF30309	Bacteroids	Nambu et al., 2015	Time-course analysis of nodulation suggests that bacteroids experience nitrogen-deficiency at early stages of nodule development.
S. meliloti 1021	Free-living cells vs. bacteroids	Djordjevic et al., 2003	Compared to free-living bacteria, nodule bacteroids appear not to require the expression of sugar transporters or enzymes involved in the early steps of glycolysis.
S. meliloti 1021	Bacteroids	Djordjevic, 2004	Bacteroids express a specific set of ABC-type transporters involved in the transport of amino acids and inorganic ions.