Data supporting the following publication: Wendlandt et al 2022, Journal of Evolutionary Biology. "Negotiating mutualism: a locus for exploitation by rhizobia has a broad effect size distribution and context-dependent effects on legume hosts." Methods We genetically disrupted the hrrP locus in 12 wild Mesorhizobium strains and inoculated the wildtype (hrrP+) and knockout mutant (hrrP-) strains onto a single genotype of Medicago polymorpha plants in greenhouse conditions. We collected data on the reproductive fitness of the wildtype and knockout mutant strains in nodules (2018_knockout_CFU_data.csv) and on plant response traits such as shoot mass and nodule count (2018_knockout_greenhouse_data.csv). In a second year, we used a subset of 5 wildtype and knockout mutant strains and inoculated them onto two genotypes of M. polymorpha in greenhouse conditions. We measured reproductive fitness of rhizobia in nodules (2019_GxG_knockout_CFU_data_330plants.csv) and plant response traits (2019_GxG_knockout_CFU_data_330plants.csv). Usage Notes We provide four datasets as csv files and one R code file that contains code for analyzing the data in these files. The contents of each file are as follows: * 2018_knockout_CFU_data.csv contains nodule culturing data (counts of colony forming units) from the 2018 Knockout Experiment * 2018_knockout_greenhouse_data.csv contains plant harvest data from the 2018 Knockout Experiment * 2019_GxG_knockout_CFU_data_330plants.csv contains nodule culturing data (counts of colony forming units) from the 2019 GxG Knockout Experiment * 2019_GxG_knockout_greenhouse_data_330plants.csv contains plant harvest data from the 2019 GxG Knockout Experiment * Wendlandt_et_al_2022_JEvolBiol_code.R contains R code for importing, processing, and analyzing data from the above four datasets. It also contains code for producing figures from these data. "2018_knockout_CFU_data" Metadata Column Description Unique.ID Unique identifier for the plant this nodule came from; only one nodule was cultured per plant, so this also uniquely identifies individual nodules Rep Technical replicate of the drop-plate assay for the nodule; nodules had up to 3 technical replicates Notes "discard" = exclude data from this row (Cami cleaned data with Miles and agreed on which rows had labeling errors or inaccurate counts due to excessive contamination); NA means no comments C.count Number of colonies that grew from a single drop of nodule slurry at dilution level C (1/500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded D.count Number of colonies that grew from a single drop of nodule slurry at dilution level D (1/2500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded E.count Number of colonies that grew from a single drop of nodule slurry at dilution level E (1/12500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded F.count Number of colonies that grew from a single drop of nodule slurry at dilution level F (1/62500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded G.count Number of colonies that grew from a single drop of nodule slurry at dilution level G (1/312500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded H.count Number of colonies that grew from a single drop of nodule slurry at dilution level H (1/1562500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded "2018_knockout_greenhouse_data" Metadata Column Description Unique.ID Unique identifier for each plant in the experiment Block Greenhouse block in which the plant was grown; ranges 1-17 (17 blocks total) Rack Unique identifier for the rack in which the plant was grown in the greenhouse; ranges 1-22; each rack held 20 plants, except for rack 22 which held 5 plants Position Numerical position of the plant within its rack; ranges 1-20 mID Unique identifier for Medicago polymorpha line; this experiment used a single plant line from the RTM population in the native range of M. polymorpha; mGenotype = W0339 eRange Range that the E. medicae strain came from; "I" = invaded range (North America); "N" = native range (Europe); "neg" = negative control (plant was not inoculated) ePop Name of the population that the E. medicae strain came from (AZN, DCR, PEA, RTM, STA); "neg" = negative control (not inoculated) eID Unique label for the E. medicae strain; wildtype strains are designated with "AE", four digits, and "P"; mutant knockout strains are denoted by "PP" followed by three digits; "neg" = uninoculated plant eStrain Genetic background of the E. medicae strain, whether it is a wildtype or knockout strain; name is composed of 3 letters indicating the source population, followed by 2-3 digits eType "WT" = E. medicae strain is the wildtype hrrP+ strain; "KO" = E. medicae strain is the mutant hrrP- knockout strain, derived from the WT strain having the same eStrain name eHrrP Presence or absence of the hrrP locus in the E. medicae strain; "1" = hrrP+; "0" = hrrP-; "neg" = uninoculated plant Leaf.Count Number of trifoliate leaves on the plant at harvest; NA means no data recorded ShootMass.G Dry shoot mass (in grams) of the plant at harvest; NA means no data recorded Flowers.Present "y" = flowers were present on the plant at harvest; NA means no data recorded Nod.Count Total number of nodules on the plant's root system, NOT including one nodule removed for culturing; NA means no data recorded "2019_GxG_knockout_CFU_data_330plants" Metadata Column Description Unique.ID Unique identifier for the plant this nodule came from; only one nodule was cultured per plant, so this also uniquely identifies individual nodules Rep Technical replicate of the drop-plate assay for the nodule; nodules had up to 3 technical replicates C.count Number of colonies that grew from a single drop of nodule slurry at dilution level C (1/500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded D.count Number of colonies that grew from a single drop of nodule slurry at dilution level D (1/2500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded E.count Number of colonies that grew from a single drop of nodule slurry at dilution level E (1/12500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded F.count Number of colonies that grew from a single drop of nodule slurry at dilution level F (1/62500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded G.count Number of colonies that grew from a single drop of nodule slurry at dilution level G (1/312500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded H.count Number of colonies that grew from a single drop of nodule slurry at dilution level H (1/1562500 of the nodule rhizobia population); 9999 = growth was saturated so that individual colonies could not be distinguished; NA means no data recorded "2019_GxG_knockout_greenhouse_data_330plants" Metadata Column Description Unique.ID Unique identifier for each plant in the experiment Block Greenhouse block in which the plant was grown; ranges B01-B15 (15 blocks total) Rack Unique identifier for the rack in which the plant was grown in the greenhouse; ranges R01-R23; each rack held 20 plants, except for rack 23 which held 10 plants Position Numerical position of the plant within its rack; ranges P01-P20 mRange Range that the M. polymorpha plant host came from; "I" = invaded range (North America); "N" = native range (Europe) mPop Name of the population that the M. polymorpha plant host came from (RTM, MEL) mGenotype Genotypic identifier for the M. polymorpha plant line (MEL population = W0405; RTM population = W0339) eRange Range that the E. medicae strain came from; "I" = invaded range (North America); "N" = native range (Europe); "neg" = negative control (plant was not inoculated) ePop Name of the population that the E. medicae strain came from (AZN, DCR, PEA, RTM); "neg" = negative control (not inoculated) eStrain Genetic background of the E. medicae strain, whether it is a wildtype or knockout strain; name is composed of 3 letters indicating the source population, followed by 2-3 digits eType "WT" = E. medicae strain is the wildtype hrrP+ strain; "KO" = E. medicae strain is the mutant hrrP- knockout strain, derived from the WT strain having the same eStrain name; "KOC_self" = E. medicae with hrrP knocked out and then complemented with the same allele that was knocked out; "KOC_Emel" = E. medicae with hrrP knocked out and then complemented with the hrrP allele from E. meliloti strain B800; "neg" = negative control (not inoculated) eHrrP Presence or absence of the hrrP locus in the E. medicae strain; "1" = hrrP+; "0" = hrrP-; "neg" = uninoculated plant ShootMass.G Dry shoot mass (in grams) of the plant at harvest; NA means no data recorded Nod.Count Total number of nodules on the plant's root system, NOT including one nodule removed for culturing; NA means no data recorded Notes "contaminated" = plant was a negative control but did form some nodules; "no_plant" = plant did not germinate or died before harvest; NA means no notes recorded