DRMY1 promotes robust morphogenesis by sustaining translation of a hormone signaling protein

Robustness is the invariant development of phenotype despite environmental changes and genetic perturbations. In the Arabidopsis flower bud, four sepals initiate at robust positions and times and grow to equal size to enclose and protect the inner floral organs. We previously characterized the mutant development related myb-like1 (drmy1), where 3-5 sepals initiate at irregular positions and variable times and grow to different sizes, compromising their protective function. The molecular mechanism underlying this loss of robustness was unclear. Here, we show that drmy1 has reduced TARGET OF RAPAMYCIN (TOR) activity, ribosomal content, and translation. Translation reduction decreases the protein level of ARABIDOPSIS RESPONSE REGULATOR7 (ARR7), a rapidly synthesized and degraded cytokinin signaling inhibitor. The resultant upregulation of cytokinin signaling disrupts the robust positioning of auxin signaling, causing variable sepal initiation. Our work shows that the homeostasis of translation, a ubiquitous cellular process, is crucial for the robust spatiotemporal patterning of organogenesis.