A Gain-of-Function Polymorphism Controlling Complex Traits and Fitness in Nature

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Science  31 Aug 2012:
Vol. 337, Issue 6098, pp. 1081-1084
DOI: 10.1126/science.1221636

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  1. Fig. 1

    (A) Histograms show percent leaf area removed by the generalist herbivore Trichoplusia ni, total quantity of glucosinolates, and proportion of aliphatic glucosinolates from branched-chain amino acid precursors (BC-GS). Greenhouse-grown plants were descended from nine B. stricta populations. (B) Map showing the proportion of genotypes in each population that produce predominantly BC-GS (white) or Met-GS (black). Parental populations of the crossing experiment are boxed.

  2. Fig. 2

    Fitness reductions under field conditions associated with 1% loss of leaf area by herbivory. Bars indicate reduction in components of fitness due to fecundity (gray) and survival (black) in 2008, 2009, and 2010 in Colorado and Montana. NIL plants in the clipping experiment were randomly assigned to artificial herbivory or control treatments. *P < 0.05, **P < 0.01, ***P < 0.001; NS, not significant.

  3. Fig. 3

    (A) Glucosinolate production in transgenic Arabidopsis expressing B. stricta BCMA genes, encoding CYP79F enzymes that catalyze amino acids in the first step of the glucosinolate pathway. Bars show amounts of aliphatic glucosinolates from Met, Val, and Ile precursors catalyzed by each of the BCMA gene products. Gene phylogeny includes wild-type (WT) Arabidopsis with empty vector controls; the black triangle identifies the gene duplication in Boechera, a red circle shows the origin of branched-chain amino acid catalysis, and a blue circle indicates elevated Ile activity. Abbreviations: B1, BCMA1; B2, BCMA2; B3, BCMA3, with alleles from Colorado (CO) or Montana (MT). N = 130 independent transgenic lines. (B) In vitro enzyme activity levels (nmol of product per nmol of enzyme per minute) relative to controls; error bars denote SE. Labels indicate CYP79F enzymes from Arabidopsis and BCMA1, BCMA2, and BCMA3 from Boechera, with alleles from Colorado or Montana. BCMA2 alleles encode identical proteins, so one allele was assayed. BCMA2 (green) retains the ancestral MET activity and was engineered to change G134L, P536K, or both (pink). *P < 0.05, **P < 0.01, ***P < 0.001.

  4. Fig. 4

    (A) Homology model of BCMA2 with the substrate-binding cleft above the heme group (magenta) with putative substrate recognition regions in purple. Amino acid changes G134L and P536K (green) show statistical evidence for accelerated protein evolution and alter catalytic function when changed by site-directed mutagenesis. Other mutations with statistical evidence of accelerated evolution (in blue) are not addressed in this study. The location of amino acid 529, which aligns with the last resolved residue in the CYP1A2 crystal structure, is colored because subsequent amino acids 530 to 540 cannot be accurately modeled. (B) Close-up view of substrate-binding cleft with mutation G134L residing just above the heme.