Fruit production is an evolutionary innovation that allows for seed dispersion. Brassica members including the model plant species Arabidopsis thaliana produce dry fruits that shatter when ripe, a process called dehiscence. The Arabidopsis fruit is a pod composed of two fused valves whose margins are joined to a central seed-bearing replum. The valve margins are specialized zones for dehiscence, related to boundaries that separate leaves from the shoot apical meristem. BLADE-ON-PETIOLE1/2 (BOP1/2) co-activators interact with Clade I TGA transcription factors to promote the activation of three-amino-acid-loop-extension (TALE) homeobox genes, important for boundary development. My data show that boundary genes enhance the expression of valve margin identity genes. Further, boundary genes are constrained to the valve margin by mechanisms similar to valve margin identity genes. Finally, boundary gene mutations modulate replum width and generate shatter-resistant fruits. Manipulation of this pathway provides a new potential strategy for optimizing pod shatter in crops.