Teosinte branched1, conventionally written tb1 for the gene, encodes a transcription factor that suppresses outgrowth of lateral buds in maize. It is a major component of the difference in apical dominance between cultivated maize and its wild teosinte relatives.
John Doebley and colleagues connected tb1 expression and mutant morphology to suppression of axillary growth. Cultivated maize showed increased tb1 expression in the relevant comparison, linking altered regulation of a developmental gene to a conspicuous domestication trait.[ref]
The evolution of apical dominance in maize by John Doebley and others. 1997, abstract: expression, mutant morphology and repression of axillary organs
This illustrates why regulatory change matters: a large difference in branching need not require inventing an entirely new protein. Changing where or how strongly an existing regulator acts can reshape the plant.
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