Protein phosphatase 2A promotes stomatal development by stabilizing SPEECHLESS in Arabidopsis

Significance The innovation of stomatal pores in plant evolution enables the success and diversification of land plants over the past 400 million years. The production and patterning of stomata are regulated by a group of deeply conserved bHLH transcription factors in land plants, with the founding member SPEECHLESS (SPCH) playing a pivotal role in the initiation of stomatal lineage. The protein stability and function of SPCH are tightly regulated by protein phosphorylation mediated by multiple kinases in Arabidopsis . Here, we establish the highly conserved PP2A protein phosphatases as positive regulators of SPCH and thus stomatal production, underscoring a key function of PP2A in fine-tuning stomatal development, a highly plastic biological process that influences many plant responses to changing environmental conditions.