title: The genetic architecture of ecophysiological and circadian traits in Brassica rapa.
abstract: Developmental mechanisms that enable perception of and response to the environment may enhance fitness. Ecophysiological traits typically vary depending on local conditions and contribute to resource acquisition and allocation, yet correlations may limit adaptive trait expression. Notably, photosynthesis and stomatal conductance vary diurnally, and the circadian clock, which is an internal estimate of time that anticipates diurnal light/dark cycles, may synchronize physiological behaviors with environmental conditions. Using recombinant inbred lines of Brassica rapa, we examined the quantitative-genetic architecture of ecophysiological and phenological traits and tested their association with the circadian clock. We also investigated how trait expression differed across treatments that simulated seasonal settings encountered by crops and naturalized populations. Many ecophysiological traits were correlated, and some correlations were consistent with expected biophysical constraints; for example, stomata jointly regulate photosynthesis and transpiration by affecting carbon dioxide and water vapor diffusion across leaf surfaces, and these traits were correlated. Interestingly, some genotypes had unusual combinations of ecophysiological traits, such as high photosynthesis in combination with low stomatal conductance or leaf nitrogen, and selection on these genotypes could provide a mechanism for crop improvement. At the genotypic and QTL level, circadian period was correlated with leaf nitrogen, instantaneous measures of photosynthesis, and stomatal conductance as well as with a long-term proxy (carbon isotope discrimination) for gas exchange, suggesting that gas exchange is partly regulated by the clock and thus synchronized with daily light cycles. The association between circadian rhythms and ecophysiological traits is relevant to crop improvement and adaptive evolution.
authors.affiliation: Department of Botany, University of Wyoming, Laramie, Wyoming 82071, USA. cedwar10@uwyo.edu
authors.forename: Christine E
authors.initials: CE
authors.lastname: Edwards
authors.forename: Brent E
authors.initials: BE
authors.lastname: Ewers
authors.forename: David G
authors.initials: DG
authors.lastname: Williams
authors.forename: Qiguang
authors.initials: Q
authors.lastname: Xie
authors.forename: Ping
authors.initials: P
authors.lastname: Lou
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Xu
authors.forename: C Robertson
authors.initials: CR
authors.lastname: McClung
authors.forename: Cynthia
authors.initials: C
authors.lastname: Weinig
mesh_terms: D029741:Brassica rapa / Q000235:genetics* / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D057906:Circadian Clocks / Q000235:genetics*; D004777:Environment; D004843:Epistasis, Genetic; D018506:Gene Expression Regulation, Plant; D056726:Genetic Association Studies; D055106:Genome-Wide Association Study; D005838:Genotype; D009584:Nitrogen / Q000378:metabolism; D010641:Phenotype; D010788:Photosynthesis / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D040641:Quantitative Trait Loci
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen