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Parallel Altitudinal Clines Reveal Adaptive Evolution Of Genome Size In Zea mays

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While the vast majority of genome size variation in plants is due to differences in repetitive sequence, we know little about how selection acts on repeat content in natural populations. Here we investigate parallel changes in intraspecific genome size and repeat content of domesticated maize (Zea mays) landraces and their wild relative teosinte across altitudinal gradients in Mesoamerica and South America. We combine genotyping, low coverage whole-genome sequence data, and flow cytometry to test for evidence of selection on genome size and individual repeat abundance. We find that population structure alone cannot explain the observed variation, implying that clinal patterns of genome size are maintained by natural selection. Our modeling additionally provides evidence of selection on individual heterochromatic knob repeats, likely due to their large individual contribution to genome size. To better understand the phenotypes driving selection on genome size, we conducted a growth chamber experiment using a population of highland teosinte exhibiting extensive variation in genome size. We find weak support for a positive correlation between genome size and cell size, but stronger support for a negative correlation between genome size and the rate of cell production. Reanalyzing published data of cell counts in maize shoot apical meristems, we then identify a negative correlation between cell production rate and flowering time. Together, our data suggest a model in which variation in genome size is driven by natural selection on flowering time across altitudinal clines, connecting intraspecific variation in repetitive sequence to important differences in adaptive phenotypes.

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Parallel Altitudinal Clines Reveal Adaptive Evolution Of Genome Size In Zea mays

  1. 1. Jeffrey Ross-Ibarra @jrossibarra • www.rilab.org Plant Sciences • Center for Population Biology • Genome Center University of California Davis Adaptive evolution of genome size along altitudinal clines in maize and teosinte
  2. 2. Abizar at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons Genome Size (bp)
  3. 3. By Nr387241 - Own work, CC BY-SA 3.0, https:// commons.wikimedia.org/w/index.php? curid=14945255 Mycoplasma (0.0006Gb) Abizar at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons Genome Size (bp)
  4. 4. By Gőtehal.jpg: Mathae derivative work: Bff (Gőtehal.jpg) [CC BY 2.5 (http:// creativecommons.org/licenses/by/2.5), CC-BY-SA-3.0 (http:// creativecommons.org/licenses/by-sa/3.0/) or GFDL (http://www.gnu.org/ copyleft/fdl.html)], via Wikimedia Commons Protopterus (130Gb) By Nr387241 - Own work, CC BY-SA 3.0, https:// commons.wikimedia.org/w/index.php? curid=14945255 Mycoplasma (0.0006Gb) Abizar at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons Genome Size (bp)
  5. 5. Genlisea (0.065Gb) By Michal Rubeš [CC BY 3.0 cz (http://creativecommons.org/ licenses/by/3.0/cz/deed.en)], via Wikimedia Commons By Gőtehal.jpg: Mathae derivative work: Bff (Gőtehal.jpg) [CC BY 2.5 (http:// creativecommons.org/licenses/by/2.5), CC-BY-SA-3.0 (http:// creativecommons.org/licenses/by-sa/3.0/) or GFDL (http://www.gnu.org/ copyleft/fdl.html)], via Wikimedia Commons Protopterus (130Gb) By Nr387241 - Own work, CC BY-SA 3.0, https:// commons.wikimedia.org/w/index.php? curid=14945255 Mycoplasma (0.0006Gb) Abizar at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons Genome Size (bp)
  6. 6. By alpsdake - Own work, CC0, https://commons.wikimedia.org/w/index.php? curid=12228596 Paris (150Gb) Genlisea (0.065Gb) By Michal Rubeš [CC BY 3.0 cz (http://creativecommons.org/ licenses/by/3.0/cz/deed.en)], via Wikimedia Commons By Gőtehal.jpg: Mathae derivative work: Bff (Gőtehal.jpg) [CC BY 2.5 (http:// creativecommons.org/licenses/by/2.5), CC-BY-SA-3.0 (http:// creativecommons.org/licenses/by-sa/3.0/) or GFDL (http://www.gnu.org/ copyleft/fdl.html)], via Wikimedia Commons Protopterus (130Gb) By Nr387241 - Own work, CC BY-SA 3.0, https:// commons.wikimedia.org/w/index.php? curid=14945255 Mycoplasma (0.0006Gb) Abizar at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons Genome Size (bp)
  7. 7. Lynch and Connnery (2003) Science
  8. 8. Whitney et al. (2010) Evolution Contrast in Ne ContrastinGenomeSize
  9. 9. Knight (2005) Ann Bot Seed Weight (+) Seed Weight GenomeSize(2Cpg) Leaf Size (-) Genome Size (2C pg) specificleafarea Whitney et al. (2010) Evolution Contrast in Ne ContrastinGenomeSize
  10. 10. maize landrace diploidgenomesize Díez et al. (2013) New Phyt
  11. 11. Z. mays ssp. parviglumis Z. mays ssp. mexicana Pyhäjärvi et al. (2013) GBE
  12. 12. Domestication 10,000BP Mexican Highlands 6,000BP S. American lowlands 6,000BP Andes 4,000BP Takuno et al. (2015) Genetics Lowland K=3K=4 Highland Lowland Highland Mesoamerica South America Lowland A B K=2K=3K=4 Highland Lowland Highland Mesoamerica South America Altitude
  13. 13. altitude GenomeSize(Mb) 77 landraces S. America Mexico parviglumis mexicana teosinte altitude3250 3125 3000 2875 2750
  14. 14. altitude GenomeSize(Mb) 77 landraces S. America Mexico teosinte 95 mexicana altitude
  15. 15. altitude GenomeSize(Mb) 77 landraces S. America Mexico teosinte 95 mexicana altitude genome size (bp) #individuals h2~0.9
  16. 16. altitude GenomeSize(Mb) 77 landraces S. America Mexico teosinte 95 mexicana altitude P = µ + alt ⇤ A + g + " g ⇠ MV N (0, VAK) " ⇠ N (0, V✏) Genome Size Altitude Additive Component Berg and Coop (2014) Plos Gen
  17. 17. altitude GenomeSize(Mb) 77 landraces S. America Mexico teosinte 95 mexicana altitude P = µ + alt ⇤ A + g + " g ⇠ MV N (0, VAK) " ⇠ N (0, V✏) Genome Size Altitude Additive Component Berg and Coop (2014) Plos Gen landraces landraces Kinship Additive Genetic Var.
  18. 18. altitude GenomeSize(Mb) 77 landraces S. America Mexico teosinte 95 mexicana altitude P = µ + alt ⇤ A + g + " g ⇠ MV N (0, VAK) " ⇠ N (0, V✏) Genome Size Altitude Additive Component Berg and Coop (2014) Plos Gen landraces landraces Kinship Additive Genetic Var. -110Kb/m -260Kb/m
  19. 19. Rosado et al. (2005) Maize Genetics Newsletter (shh, secret) Knob180 KnobTR1 Maize TEs Sorghum TEs Jiao et al. (2017) Nature copy number
  20. 20. Rosado et al. (2005) Maize Genetics Newsletter (shh, secret) Knob180 KnobTR1 Maize TEs Sorghum TEs Jiao et al. (2017) Nature copy number
  21. 21. Rosado et al. (2005) Maize Genetics Newsletter (shh, secret) Knob180 KnobTR1 Maize TEs Sorghum TEs Jiao et al. (2017) Nature copy number
  22. 22. r2=0.77 r2=0.74
  23. 23. P = µ + alt ⇤ A + GS ⇤ GS + g + " g ⇠ MV N (0, VAK) " ⇠ N (0, V✏) AltitudeRepeat Genome Size as Covariate Additive Component
  24. 24. altitude B-repeatreads
  25. 25. altitude MbTE maize mexicana S. America Mexico Region
  26. 26. altitude MbTE maize mexicana S. America Mexico Region altitude knob180 knobTR1 Knobabundance(Mb) maize mexicana maize mexicana
  27. 27. High SAm Mex SAm Mex Low Flint-Garcia et al. (unpublished) floweringtime(days)
  28. 28. Nature Education 2013 https://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/113371527/14707478.jpg DNA Replication Francis et al. (2008) Ann Bot FIG. 2. DNA C-value (pg) and cell cycle time (h) in the root apic istem of a range of (A) eudicots and monocots (n ¼ 110), and (B) e (n ¼ 60). See Table 2 for regression analyses.
  29. 29. Bennett (1972) Proc Roy Soc B #species cellcycletime(h) annual perennial annual perennial genome size (pg of 3C)
  30. 30. mother(n=202plants) genome size
  31. 31. Leaf Elongation (LER) Cell Size (CS) Cell Production (CP) Genome Size (GS) + - log(CP) = 0 + GS ⇤ log(GS) log(LER) = ⌧0 + ⌧GS ⇤ log(GS) log(CS) = 0 + GS ⇤ log(GS) GS = ⌧GS GS Posterior Density of βGS Posterior Density of γGS Šímová and Herben (2012) Proc Roy Soc B Walker and Smith (2002) Development
  32. 32. Leaf Elongation (LER) Cell Size (CS) Cell Production (CP) Genome Size (GS) + - log(CP) = 0 + GS ⇤ log(GS) log(LER) = ⌧0 + ⌧GS ⇤ log(GS) log(CS) = 0 + GS ⇤ log(GS) GS = ⌧GS GS Posterior Density of βGS Posterior Density of γGS Šímová and Herben (2012) Proc Roy Soc B Walker and Smith (2002) Development
  33. 33. Leiboff et al. (2015) Nat Comm cell number (cell division rate)floweringtime growth stage
  34. 34. 1. Genome size is a quantitative trait that can affect fitness, and observed intraspecific variation may be adaptive 2. Selection for faster development leads to smaller genomes across altitudinal clines in maize and teosinte 3. Selection on genome size likely impacts the evolution of individual repeat classes
  35. 35. Acknowledgements U Missouri Patrice Albert Jim Birchler Cornell Kelly Swarts UC Davis Jeremy Berg Graham Coop Mark Grote Juvenal Quesada Plant Genome Research Program HiLo Lab Alumni Paul Bilinski (West Shore College) Anna O’Brien (U Toronto) Jinliang Yang (U Nebraska-Lincoln)
  36. 36. large small GENOME SIZE
  37. 37. large small GENOME SIZE slow fast CELL DIVISION Density of βGS
  38. 38. large small GENOME SIZE late early FLOWERING TIME slow fast CELL DIVISION Density of βGS

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