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Ultrasensitive feedback control can improve robust gene expressions in cell populations, yet it usually requires large chemical productions that cause severe burden to cells. Inspired by `division-of-labor' in heterogeneous populations, we propose a bistable switch circuit that utilizes quorum sensing systems to coordinate heterogeneous phenotypes' behaviors. We show that ultrasensitivity emerges from a collection of parallel bistable switches in individual cells. When applied to feedback control of population level expressions, it can achieve robust reference tracking and adaptation to disturbances. In particular, we demonstrate that molecular sequestration enables tunable hysteresis in single switches, leading to a wide range of stable population level expressions. 

Summary Fossil discoveries can transform our understanding of plant diversification over time and space. Recently described fossils in many plant families have pushed their known records farther back in time, pointing to alternative scenarios for their origin and spread.Here, we describe two new Eocene fossil berries of the nightshade family (Solanaceae) from the Esmeraldas Formation in Colombia and the Green River Formation in Colorado (USA). The placement of the fossils was assessed using clustering and parsimony analyses based on 10 discrete and five continuous characters, which were also scored in 291 extant taxa.The Colombian fossil grouped with members of the tomatillo subtribe, and the Coloradan fossil aligned with the chili pepper tribe. Along with two previously reported early Eocene fossils from the tomatillo genus, these findings indicate that Solanaceae were distributed at least from southern South America to northwestern North America by the early Eocene.Together with two other recently discovered Eocene berries, these fossils demonstrate that the diverse berry clade and, in turn, the entire nightshade family, is much older and was much more widespread in the past than previously thought.