Abstract:Under nitrogen‐limiting conditions, legumes are able to form a symbiotic interaction with bacteria of the Rhizobiaceae family to produce root nodules. These new root organs satisfy plant nitrogen needs by reducing atmospheric nitrogen to ammonium. However, the senescence of these organs disturbs the assimilation of nitrogen. In this study, we present different histological, biochemical, and genetic markers of the natural nodule senescence in Medicago truncatula over a 10‐week period following bacterial inocula… Show more
“…While this germination and establishment fraction was lower than our past work with Medicago (and these lines), we verified that the total fraction of germinants was not correlated with the focal traits analyzed below (|r| < 0.19, P > 0.17), suggesting that germination and establishment variation did not bias our estimates of plant performance or nodulation. The experiment was terminated at 9 weeks to prevent nodule senescence ( Puppo et al., 2005 ; El Msehli et al., 2019 ), at which point 409 (61%) plants had flowered. We found 25 ± 6.50 (mean ± S.E.)…”
The maintenance of genetic variation in mutualism-related traits is key for understanding mutualism evolution, yet the mechanisms maintaining variation remain unclear. We asked whether genotype-by-environment (G×E) interaction is a potential mechanism maintaining variation in the model legume–rhizobia system,
Medicago truncatula–Ensifer meliloti
. We planted 50 legume genotypes in a greenhouse under ambient light and shade to reflect reduced carbon availability for plants. We found an expected reduction under shaded conditions for plant performance traits, such as leaf number, aboveground and belowground biomass, and a mutualism-related trait, nodule number. We also found G×E for nodule number, with ∼83% of this interaction due to shifts in genotype fitness rank order across light environments, coupled with strong positive directional selection on nodule number regardless of light environment. Our results suggest that G×E can maintain genetic variation in a mutualism-related trait that is under consistent positive directional selection across light environments.
“…While this germination and establishment fraction was lower than our past work with Medicago (and these lines), we verified that the total fraction of germinants was not correlated with the focal traits analyzed below (|r| < 0.19, P > 0.17), suggesting that germination and establishment variation did not bias our estimates of plant performance or nodulation. The experiment was terminated at 9 weeks to prevent nodule senescence ( Puppo et al., 2005 ; El Msehli et al., 2019 ), at which point 409 (61%) plants had flowered. We found 25 ± 6.50 (mean ± S.E.)…”
The maintenance of genetic variation in mutualism-related traits is key for understanding mutualism evolution, yet the mechanisms maintaining variation remain unclear. We asked whether genotype-by-environment (G×E) interaction is a potential mechanism maintaining variation in the model legume–rhizobia system,
Medicago truncatula–Ensifer meliloti
. We planted 50 legume genotypes in a greenhouse under ambient light and shade to reflect reduced carbon availability for plants. We found an expected reduction under shaded conditions for plant performance traits, such as leaf number, aboveground and belowground biomass, and a mutualism-related trait, nodule number. We also found G×E for nodule number, with ∼83% of this interaction due to shifts in genotype fitness rank order across light environments, coupled with strong positive directional selection on nodule number regardless of light environment. Our results suggest that G×E can maintain genetic variation in a mutualism-related trait that is under consistent positive directional selection across light environments.
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