A gene for genetic background inZea mays: fine-mappingenhancer of teosinte branched1.2(etb1.2) to a YABBY class transcription factor
ABSTRACTThe effects of an allelic substitution at a gene often depend critically on genetic background, the genotype at other genes in the genome. During the domestication of maize from its wild ancestor (teosinte), an allelic substitution atteosinte branched(tb1) caused changes in both plant and ear architecture. The effects oftb1on phenotype were shown to depend on multiple background loci including one called enhancer oftb1.2 (etb1.2).We mappedetb1.2to a YABBY class transcription factor (ZmYAB2.1) and showed that the maize alleles ofZmYAB2.1are either expressed at a lower level than teosinte alleles or disrupted by insertions in the sequences.tb1andetb1.2interact epistatically to control the length of internodes within the maize ear which affects how densely the kernels are packed on the ear. The interaction effect is also observed at the level of gene expression withtb1acting as a repressor ofZmYAB2.1expression. Curiously,ZmYAB2.1was previously identified as a candidate gene for another domestication trait in maize, non-shattering ears. Consistent with this proposed role,ZmYAB2.1is expressed in a narrow band of cells in immature ears that appears to represent a vestigial abscission (shattering) zone. Expression in this band of cells may also underlie the effect on internode elongation. The identification ofZmYAB2.1as a background factor interacting withtb1is a first step toward a gene-level understanding of howtb1and the background within which it works evolved in concert during maize domestication.