Vann et al . : Variation in teosinte at the tb 1 locus Natural variation in teosinte at the domestication locus teosinte branched 1 ( tb 1 ) 1

1 Premise of the study: The teosinte branched1 (tb1 ) gene is a major QTL controlling branching 2 differences between maize and its wild progenitor, teosinte. The insertion of a transposable 3 element (Hopscotch) upstream of tb1 is known to enhance the gene’s expression, causing reduced 4 tillering in maize. Observations of the maize tb1 allele in teosinte and estimates of an insertion 5 age of the Hopscotch that predates domestication led us to investigate its prevalence and 6 potential role in teosinte. 7 Methods: Prevalence of the Hopscotch element was assessed across an Americas-wide sample of 8 1110 maize and teosinte individuals using a co-dominant PCR assay. Population genetic 9 summaries were calculated for a subset of individuals from four teosinte populations in central 10 Mexico. Phenotypic data were also collected from a single teosinte population where Hopscotch 11 was found segregating. 12 Key results: Genotyping results suggest the Hopscotch element is at higher than expected 13 frequency in teosinte. Analysis of linkage disequilibrium near tb1 does not support recent 14 introgression of the Hopscotch allele from maize into teosinte. Population genetic signatures are 15 consistent with selection on this locus revealing a potential ecological role for Hopscotch in 16 teosinte. Finally, two greenhouse experiments with teosinte do not suggest tb1 controls tillering in 17 natural populations. 18 Conclusions: Our findings suggest the role of Hopscotch differs between maize and teosinte. 19 Future work should assess tb1 expression levels in teosinte with and without the Hopscotch and 20 more comprehensively phenotype teosinte to assess the ecological significance of the Hopscotch 21 insertion and, more broadly, the tb1 locus in teosinte. 22