Cell cycle regulates cell type in the Arabidopsis sepal
ABSTRACT The formation of cellular patterns during development requires the coordination of cell division with cell identity specification. This coordination is essential in patterning the highly elongated giant cells, which are interspersed between small cells, in the outer epidermis of the Arabidopsis thaliana sepal. Giant cells undergo endocycles, replicating their DNA without dividing, whereas small cells divide mitotically. We show that distinct enhancers are expressed in giant cells and small cells, indicating that these cell types have different identities as well as different sizes. We find that members of the epidermal specification pathway, DEFECTIVE KERNEL1 (DEK1), MERISTEM LAYER1 (ATML1), Arabidopsis CRINKLY4 (ACR4) and HOMEODOMAIN GLABROUS11 (HDG11), control the identity of giant cells. Giant cell identity is established upstream of cell cycle regulation. Conversely, endoreduplication represses small cell identity. These results show not only that cell type affects cell cycle regulation, but also that changes in the cell cycle can regulate cell type.
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ABSTRACT: AINTEGUMENTA-LIKE (AIL) transcription factors are key regulators of cell proliferation and meristem identity. Although AIL functions have been well described, the direct signalling components of this pathway are largely unknown. We show that BABY BOOM (BBM) and other AIL proteins physically interact with multiple members of the L1-expressed HOMEODOMAIN GLABROUS (HDG) transcription factor family, including HDG1, HDG11 and HDG12. Overexpression of HDG1, HDG11 and HDG12 restricts growth due to root and shoot meristem arrest, which is associated with reduced expression of genes involved in meristem development and cell proliferation pathways, whereas downregulation of multiple HDG genes promotes cell overproliferation. These results suggest a role for HDG proteins in promoting cell differentiation. We also reveal a transcriptional network in which BBM and HDG1 regulate several common target genes, and where BBM/AIL and HDG regulate the expression of each other. Taken together, these results suggest opposite roles for AIL and HDG proteins, with AILs promoting cell proliferation and HDGs stimulating cell differentiation, and that these functions are mediated at both the protein-protein interaction and transcriptional level. © 2015. Published by The Company of Biologists Ltd.Development 01/2015; 142(3). DOI:10.1242/dev.117168 · 6.27 Impact Factor
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ABSTRACT: Size is a critical property of a cell, but how it is determined is still not well understood. The sepal epidermis of Arabidopsis thaliana contains cells with a diversity of sizes ranging from giant cells to small cells. Giant cells have undergone endoreduplication, a specialized cell cycle in which cells replicate their DNA, but fail to divide, becoming polyploid and enlarged. Through forward genetics, we have identified a new mutant with ectopic giant cells covering the sepal epidermis. Surprisingly, the mutated gene, SEC24A, encodes a COPII vesicle coat subunit involved in ER to Golgi trafficking in the early secretory pathway. We show that the ectopic giant cells of sec24a-2 are highly endoreduplicated and that their formation requires the activity of giant cell pathway genes, LOSS OF GIANT CELLS FROM ORGANS (LGO), DEFECTIVE KERNEL1 (DEK1) and Arabidopsis CRINKLY4 (ACR4). In contrast to other trafficking mutants, cytokinesis appears to occur normally in sec24a-2. Our study reveals an unexpected yet specific role of SEC24A in endoreduplication and cell size patterning in the Arabidopsis sepal.Plant physiology 10/2014; DOI:10.1104/pp.114.246033 · 7.39 Impact Factor
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ABSTRACT: Plants, along with other multicellular organisms, have evolved specialized regulatory mechanisms to achieve proper tissue growth and morphogenesis. During development, growing tissues generate specialized cell types and complex patterns necessary for establishing the function of the organ. Tissue growth is a tightly regulated process that yields highly reproducible outcomes. Nevertheless, the underlying cellular and molecular behaviors are often stochastic. Thus, how does stochasticity, together with strict genetic regulation, give rise to reproducible tissue development? This review draws examples from plants as well as other systems to explore stochasticity in plant cell division, growth, and patterning. We conclude that stochasticity is often needed to create small differences between identical cells, which are amplified and stabilized by genetic and mechanical feedback loops to begin cell differentiation. These first few differentiating cells initiate traditional patterning mechanisms to ensure regular development.Frontiers in Plant Science 09/2014; 5:420. DOI:10.3389/fpls.2014.00420 · 3.64 Impact Factor