Abstract
Regulated gene expression is key to the orchestrated progression of the cell cycle. Many genes are expressed at specific points in the cell cycle, including important cell cycle regulators, plus factors involved in signal transduction, hormonal regulation, and metabolic control. We demonstrate that post-embryonic depletion of Arabidopsis (Arabidopsis thaliana) ARGONAUTE1 (AGO1), the main effector of plant microRNAs (miRNAs), impairs cell division in the root meristem. We utilized the highly synchronizable tobacco (Nicotiana tabacum) Bright yellow 2 (BY2) cell suspension to analyze mRNA, small RNAs, and mRNA cleavage products of synchronized BY2 cells at S, G2, M, and G1 phases of the cell cycle. This revealed that in plants, only a few miRNAs show differential accumulation during the cell cycle, and miRNA-target pairs were only identified for a small proportion of the more than 13,000 differentially expressed genes during the cell cycle. However, this unique set of miRNA-target pairs could be key to attenuate the expression of several transcription factors and disease resistance genes. We also demonstrate that AGO1 binds to a set of 19-nucleotide, tRNA-derived fragments during the cell cycle progression.
Highlights
In all eukaryotes, the basic principles controlling cell division appear to be conserved (Nurse, 2000)
The cell cycle is composed of four phases: in gap phase 1 (G1), cells increase their number of organelles; during S phase DNA replication occurs; in gap phase 2 (G2), cells still increase their size by extensive protein synthesis; and in mitosis (M) phase, chromosomes segregate into two nuclei, followed by cytokinesis, during which cells are divided into two daughter cells
The strong effect of P0 on meristem size and cell division activity was significantly suppressed in ago1-57 (Figures 1A and 1B), indicating that this phenotype is mainly dependent on AGO1
Summary
The basic principles controlling cell division appear to be conserved (Nurse, 2000). The orchestration of the cell cycle, and especially the transition from G1 to S phase as well as the progression and exit from M phase, requires multiple levels of control. Cyclin-dependent kinases (CDKs) that are activated by cyclins are key players in this process (Malumbres and Barbacid, 2005; De Veylder et al, 2007). Several other kinases and phosphatases, as well as additional regulatory proteins, such as CDK inhibitors, regulate progression through the cell cycle (Boutros et al, 2006; Fisher, 2012; Starostina and Kipreos, 2012). In Arabidopsis (Arabidopsis thaliana), and plants in general, most core cell cycle genes are conserved (Vandepoele et al, 2002), several are present in multiple copies.
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