Studies of cell identity factors reveal their role in cell differentiation, polar growth and DNA segregation
Caulobacter crescentus and Agrobacterium tumefaciens display different growth modes. Indeed, Caulobacter elongates through dispersed growth, whereas Agrobacterium elongates through single polar growth. In this thesis, “Studies of cell identity factors reveal their role in cell differentiation, polar growth and DNA segregation”, I studied cell pole identity factors of Caulobacter and Agrobacterium. I observed that, 1) the subcellular accumulation of a swarmer pole determinant is inhibited by a stalked pole determinant in Caulobacter; that 2) a previously uncharacterized Agrobacterium protein, with little amino acid sequence identity to a land mark protein of Caulobacter, forms at the growth pole a striking hexameric ring required for polar growth; that 3) the four Agrobacterium genetic elements exhibit different timing of replication and segregation, and that specific old pole and growth pole markers are critically required for the segregation of the two essential replicons of Agrobacterium; and that 4) the localization of an ATPase protein, likely required for DNA segregation in Agrobacterium, requires rod shape morphology dependent on two specific growth pole markers. These insights indicate that polar growth cell cycle requires different structures and cell identity factors with distinct functional roles when compared to dispersed growth cell cycle.
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