Research Article

Cell size controlled in plants using DNA content as an internal scale

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Science  11 Jun 2021:
Vol. 372, Issue 6547, pp. 1176-1181
DOI: 10.1126/science.abb4348

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Cell size set by cell cycle regulation

In the Arabidopsis meristem, cell sizes are regularized despite asymmetric cell divisions. D'Ario et al. describe a balanced regulatory system that controls the duration of the growth phase of the cell cycle preceding DNA synthesis. KIP-related protein 4 (KRP4) inhibits progression to DNA synthesis. Because the amount of KRP4, which binds to mitotic chromosomes, is titrated to the amount of chromosomal DNA, daughter cells begin with similar amounts of KRP4 despite possible asymmetric cell divisions. Deviations are adjusted as excess KRP4 is degraded and the cell size is normalized.

Science, abb4348, this issue p. 1176

Abstract

How eukaryotic cells assess and maintain sizes specific for their species and cell type remains unclear. We show that in the Arabidopsis shoot stem cell niche, cell size variability caused by asymmetric divisions is corrected by adjusting the growth period before DNA synthesis. KIP-related protein 4 (KRP4) inhibits progression to DNA synthesis and associates with mitotic chromosomes. The F BOX-LIKE 17 (FBL17) protein removes excess KRP4. Consequently, daughter cells are born with comparable amounts of KRP4. Inhibitor dilution models predicted that KRP4 inherited through chromatin would robustly regulate size, whereas inheritance of excess free KRP4 would disrupt size homeostasis, as confirmed by mutant analyses. We propose that a cell cycle regulator, stabilized by association with mitotic chromosomes, reads DNA content as a cell size–independent scale.

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