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