MUTE Directly Orchestrates Cell-State Switch and the Single Symmetric Division to Create Stomata

Precise cell division control is critical for developmental patterning. For the differentiation of a functional stoma, a cellular valve for efficient gas exchange, the single symmetric division of an immediate precursor is absolutely essential. Yet, the mechanism governing this event remains unclear. Here we report comprehensive inventories of gene expression by the Arabidopsis bHLH protein MUTE, a potent inducer of stomatal differentiation. MUTE switches the gene expression program initiated by SPEECHLESS. MUTE directly induces a suite of cell-cycle genes, including CYCD5;1, in which introduced expression triggers the symmetric divisions of arrested precursor cells in mute, and their transcriptional repressors, FAMA and FOUR LIPS. The regulatory network initiated by MUTE represents an incoherent type 1 feed-forward loop. Our mathematical modeling and experimental perturbations support a notion that MUTE orchestrates a transcriptional cascade leading to a tightly restricted pulse of cell-cycle gene expression, thereby ensuring the single cell division to create functional stomata.