Due to their sessile lifestyle, plants are especially exposed to various stresses, including genotoxic stress, which results in altered genome integrity. Upon the detection of DNA damage, distinct ...cellular responses lead to cell cycle arrest and the induction of DNA repair mechanisms. Interestingly, it has been shown that some cell cycle regulators are not only required for meristem activity and plant development but are also key to cope with the occurrence of DNA lesions. In this review, we first summarize some important regulatory steps of the plant cell cycle and present a brief overview of the DNA damage response (DDR) mechanisms. Then, the role played by some cell cycle regulators at the interface between the cell cycle and DNA damage responses is discussed more specifically.
Phytohormones regulate plant growth from cell division to organ development. Jasmonates (JAs) are signaling molecules that have been implicated in stress-induced responses. However, they have also ...been shown to inhibit plant growth, but the mechanisms are not well understood. The effects of methyl jasmonate (MeJA) on leaf growth regulation were investigated in Arabidopsis (Arabidopsis thaliana) mutants altered in JA synthesis and perception, allene oxide synthase and coil-16B (for coronatine insensitive1), respectively. We show that MeJA inhibits leaf growth through the JA receptor COI1 by reducing both cell number and size. Further investigations using flow cytometry analyses allowed us to evaluate ploidy levels and to monitor cell cycle progression in leaves and cotyledons of Arabidopsis and/or Nicotiana benthamiana at different stages of development. Additionally, a novel global transcription profiling analysis involving continuous treatment with MeJA was carried out to identify the molecular players whose expression is regulated during leaf development by this hormone and COI1. The results of these studies revealed that MeJA delays the switch from the mitotic cell cycle to the endoreduplication cycle, which accompanies cell expansion, in a COI1 -dependent manner and inhibits the mitotic cycle itself, arresting cells in G1 phase prior to the S-phase transition. Significantly, we show that MeJA activates critical regulators of endoreduplication and affects the expression of key determinants of DNA replication. Our discoveries also suggest that MeJA may contribute to the maintenance of a cellular "stand-by mode" by keeping the expression of ribosomal genes at an elevated level. Finally, we propose a novel model for MeJA-regulated COI1 -dependent leaf growth inhibition.
Most cellular proteins involved in genome replication are conserved in all eukaryotic lineages including yeast, plants and animals. However, the mechanisms controlling their availability during the ...cell cycle are less well defined. Here we show that the Arabidopsis genome encodes for two ORC1 proteins highly similar in amino acid sequence and that have partially overlapping expression domains but with distinct functions. The ancestral ORC1b gene, present before the partial duplication of the Arabidopsis genome, has retained the canonical function in DNA replication. ORC1b is expressed in both proliferating and endoreplicating cells, accumulates during G1 and is rapidly degraded upon S-phase entry through the ubiquitin-proteasome pathway. In contrast, the duplicated ORC1a gene has acquired a specialized function in heterochromatin biology. ORC1a is required for efficient deposition of the heterochromatic H3K27me1 mark by the ATXR5/6 histone methyltransferases. The distinct roles of the two ORC1 proteins may be a feature common to other organisms with duplicated ORC1 genes and a major difference with animal cells.
A key step of the cell cycle is the entry into the DNA replication phase that typically commits cells to divide. However, little is known about the molecular mechanisms regulating this transition in ...plants. Here, we investigated the function of FBL17 (F BOX-LIKE17), an Arabidopsis thaliana F-box protein previously shown to govern the progression through the second mitosis during pollen development. Our work reveals that FBL17 function is not restricted to gametogenesis. FBL17 transcripts accumulate in both proliferating and postmitotic cell types of Arabidopsis plants. Loss of FBL17 function drastically reduces plant growth by altering cell division activity in both shoot and root apical meristems. In fbl17 mutant plants, DNA replication is severely impaired and endoreplication is fully suppressed. At the molecular level, lack of FBL17 increases the stability of the CDK (CYCLIN-DEPENDENT KINASE) inhibitor KIP-RELATED PROTEIN2 known to switch off CDKA;1 kinase activity. Despite the strong inhibition of cell proliferation in fbl17, some cells are still able to enter S phase and eventually to divide, but they exhibit a strong DNA damage response and often missegregate chromosomes. Altogether, these data indicate that the F-box protein FBL17 acts as a master cell cycle regulator during the diploid sporophyte phase of the plant.
The plant cell cycle is tightly regulated by factors that integrate endogenous cues and environmental signals to adapt plant growth to changing conditions. Under drought, cell division in young ...leaves is blocked by an active mechanism, reducing the evaporative surface and conserving energy resources. The molecular function of cyclin-dependent kinase-inhibitory proteins (CKIs) in regulating the cell cycle has already been well studied, but little is known about their involvement in cell cycle regulation under adverse growth conditions. In this study, we show that the transcript of the CKI gene SIAMESE-RELATED1 (SMR1) is quickly induced under moderate drought in young Arabidopsis (Arabidopsis thaliana) leaves. Functional characterization further revealed that SMR1 inhibits cell division and affects meristem activity, thereby restricting the growth of leaves and roots. Moreover, we demonstrate that SMR1 is a short-lived protein that is degraded by the 26S proteasome after being ubiquitinated by a Cullin-RING E3 ubiquitin ligase. Consequently, overexpression of a more stable variant of the SMR1 protein leads to a much stronger phenotype than overexpression of the native SMR1. Under moderate drought, both the SMR1 transcript and SMR1 protein accumulate. Despite this induction, smr1 mutants do not show overall tolerance to drought stress but do show less growth inhibition of young leaves under drought. Surprisingly, the growth-repressive hormone ethylene promotes SMR1 induction, but the classical drought hormone abscisic acid does not.
The male gametophyte (or pollen) plays an obligatory role during sexual reproduction of higher plants. The extremely reduced complexity of this organ renders pollen a valuable experimental system for ...studying fundamental aspects of plant biology such as cell fate determination, cell–cell interactions, cell polarity, and tip-growth. Here, we present the first reference map of the mature pollen proteome of the dicotyledonous model plant species,
Arabidopsis thaliana. Based on two-dimensional gel electrophoresis, matrix-assisted laser desorption/ionization time-of-flight, and electrospray quadrupole time-of-flight mass spectrometry, we reproducibly identified 121 different proteins in 145 individual spots. The presence, subcellular localization, and functional classification of the identified proteins are discussed in relation to the pollen transcriptome and the full protein complement encoded by the nuclear
Arabidopsis genome.
Abstract The two invasive Reynoutria species, Reynoutria japonica var. japonica and Reynoutria sachalinensis , and their hybrid Reynoutria x bohemica are often misidentified by managers and ...nonspecialists. The taxonomic confusions are all the more exacerbated by the infraspecific variability of introduced populations in terms of morphology, genetic diversity, and ploidy level. We resolved the identity of North‐Eastern French invasive populations using 4582 single‐nucleotide polymorphisms (SNPs) from a RADseq analysis, DNA contents estimated by flow cytometry, and 12 vegetative morphometric variables. The SNPs supported only one single genotype for R. japonica over 11 localities, while the nine localities of Reynoutria x bohemica were represented by one genotype each. Estimation of genome size using DAPI staining and flow cytometry revealed only octoploid cytotypes for R. japonica and hexaploid cytotypes for R . x bohemica , whereas R. sachalinensis was represented by tetraploid and hexaploid cytotypes. Among morphometric variables, no single one allows for a clear differentiation of the three taxa. We propose a combination of characters to easily and quickly identify these three invasive taxa based on six vegetative criteria including leaf and apex length, as well as leaf shape, leaf base, and apex shape, and the extrafloral nectaries on the node.
The mutation of FBL17 leads to a strong upregulation of genes involved in DNA damage and repair processes, and FBL17 protein is recruited at nuclear DNA lesion foci upon double-strand break ...induction.
In Arabidopsis (
Arabidopsis thaliana
), the F-box protein F-BOX-LIKE17 (FBL17) was previously identified as an important cell-cycle regulatory protein. FBL17 is required for cell division during pollen development and for normal cell-cycle progression and endoreplication during the diploid sporophyte phase. FBL17 was reported to control the stability of the CYCLIN-DEPENDENT KINASE inhibitor KIP-RELATED PROTEIN (KRP), which may underlie the drastic reduction in cell division activity in both shoot and root apical meristems observed in
fbl17
loss-of-function mutants. However, whether FBL17 has other substrates and functions besides degrading KRPs remains poorly understood. Here we show that mutation of
FBL17
leads not only to misregulation of cell cycle genes, but also to a strong upregulation of genes involved in DNA damage and repair processes. This phenotype is associated with a higher frequency of DNA lesions in
fbl17
and increased cell death in the root meristem, even in the absence of genotoxic stress. Notably, the constitutive activation of DNA damage response genes is largely SOG1-independent in
fbl17
. In addition, through analyses of root elongation, accumulation of cell death, and occurrence of γH2AX foci, we found that
fbl17
mutants are hypersensitive to DNA double-strand break-induced genotoxic stress. Notably, we observed that the FBL17 protein is recruited at nuclear foci upon double-strand break induction and colocalizes with γH2AX, but only in the presence of RETINOBLASTOMA RELATED1. Altogether, our results highlight a role for FBL17 in DNA damage response, likely by ubiquitylating proteins involved in DNA-damage signaling or repair.
Plant growth control has become a major focus due to economic reasons and results from a balance of cell proliferation in meristems and cell elongation that occurs during differentiation. Research on ...plant cell proliferation over the last two decades has revealed that the basic cell-cycle machinery is conserved between human and plants, although specificities exist. While many regulatory circuits control each step of the cell cycle, the ubiquitin proteasome system (UPS) appears in fungi and metazoans as a major player. In particular, the UPS promotes irreversible proteolysis of a set of regulatory proteins absolutely required for cell-cycle phase transitions. Not unexpectedly, work over the last decade has brought the UPS to the forefront of plant cell-cycle research. In this review, we will summarize our knowledge of the function of the UPS in the mitotic cycle and in endoreduplication, and also in meiosis in higher plants.
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