Biomedical subjects

Bénédicte Desvoyes

Publications and source records attributed to Bénédicte Desvoyes.

7 recordsLinked to original sources

PubMed2005

Cell type-specific role of the retinoblastoma/E2F pathway during Arabidopsis leaf development.

Organogenesis in plants is almost entirely a postembryonic process. This unique feature implies a strict coupling of cell proliferation and differentiation, including cell division, arrest, cell cycle reactivation, endoreplication, and differentiation. The plant retinoblastoma-related (RBR) protein modulates the activity of E2F transcription factors to restrict cell proliferation. Arabidopsis contains a single RBR gene, and its loss of function precludes gamete formation and early development. To determine the relevance of the RBR/E2F pathway during organogenesis, outside its involvement in cell division, we have used an inducible system to inactivate RBR function and release E2F activity. Here, we have focused on leaves where cell proliferation and differentiation are temporally and developmentally regulated. Our results reveal that RBR restricts cell division early during leaf development when cell proliferation predominates, while it regulates endocycle occurrence at later stages. Moreover, shortly after leaving the cell cycle, most of leaf epidermal pavement cells retain the ability to reenter the cell cycle and proliferate, but maintain epidermal cell fate. On the contrary, mesophyll cells in the inner layers do not respond in this way to RBR loss of activity. We conclude that there exists a distinct response of different cells to RBR inactivation in terms of maintaining the balance between cell division and endoreplication during Arabidopsis (Arabidopsis thaliana) leaf development.

Arabidopsis↗

PubMed2005

The genes encoding Arabidopsis ORC subunits are E2F targets and the two ORC1 genes are differently expressed in proliferating and endoreplicating cells.

Initiation of eukaryotic DNA replication depends on the function of pre-replication complexes (pre-RC), one of its key component being the six subunits origin recognition complex (ORC). In spite of a significant degree of conservation among ORC proteins from different eukaryotic sources, the regulation of their availability varies considerably in different model systems and cell types. Here, we show that the six ORC genes of Arabidopsis thaliana are regulated at the transcriptional level during cell cycle and development. We found that Arabidopsis ORC genes, except AtORC5, contain binding sites for the E2F family of transcription factors. Expression of AtORC genes containing E2F binding sites peaks at the G1/S-phase. Analysis of AtORC gene expression in plants with reduced E2F activity, obtained by expressing a dominant negative version of DP, the E2F heterodimerization partner, and with increased E2F activity, obtained by inactivation of the retinoblastoma protein, led us to conclude that all AtORC genes, except AtORC5 are E2F targets. Interestingly, Arabidopsis contains two AtORC1 (a and b) genes, highly conserved at the amino acid level but with unrelated promoter sequences. AtORC1b expression is restricted to proliferating cells. However, AtORC1a is preferentially expressed in endoreplicating cells based on our analysis in endoreplicating tissues and in a mutant with altered endocycle pattern. This suggests a differential expression of the two ORC1 genes in Arabidopsis.

Arabidopsis↗

PubMed2005

Balance between cell division and differentiation during plant development.

The processes which make possible that a cell gives rise to two daughter cells define the cell division cycle. In individual cells, this is strictly controlled both in time and space. In multicellular organisms extra layers of regulation impinge on the balance between cell proliferation and cell differentiation within particular ontogenic programs. In contrast to animals, organogenesis in plants is a post-embryonic process that requires developmentally programmed reversion of sets of cells from different differentiated states to a pluripotent state followed by regulated proliferation and progression through distinct differentiation patterns. This implies a fine coupling of cell division control, cell cycle arrest and reactivation, endoreplication and differentiation. The emerging view is that cell cycle regulators, in addition to controlling cell division, also function as targets for maintaining cell homeostasis during development. The mechanisms and cross talk among different cell cycle regulatory pathways are discussed here in the context of a developing plant.

Arabidopsis↗

PubMed2004

The multifunctional plant viral suppressor of gene silencing P19 interacts with itself and an RNA binding host protein.

Tomato bushy stunt virus (TBSV) is an RNA plant virus encoding a protein of approximately 19 kDa (P19) that is involved in various activities important for pathogenicity, including virus transport and suppression of gene silencing. In this study, we provide evidence in vivo and in vitro that P19 specifically interacts with itself to predominantly form dimers, and with a novel host protein, Hin19. Hin19 has a high degree of similarity with a class of RNA-binding proteins of which many are involved in RNA processing. The binding of P19 to itself and to Hin19 both depend on a structurally important central region of P19 that was previously shown critical for its biological function in plants. Our findings provide evidence for a model in which virus spread through suppression of defense-related gene silencing involves the formation of a complex that includes P19 dimers and a newly identified host RNA-binding protein.

Amino Acid Sequence↗

PubMed2002

Host-dependent recombination of a Tomato bushy stunt virus coat protein mutant yields truncated capsid subunits that form virus-like complexes which benefit systemic spread.

This study examined the contribution of the Tomato bushy stunt virus (TBSV) coat protein (CP) and its corresponding RNA to systemic infection of plants. Compared to results obtained with a mutant lacking the 5'-half of the CP gene, the presence of those CP-RNA sequences in another mutant benefited TBSV infection on Nicotiana benthamiana even though wild-type CP expression was eliminated by introduction of a small out-of-frame deletion. RT-PCR of viral RNA associated with rapid infections established by this CP frameshift deletion mutant revealed that in planta recombination had provided the progeny with the ability to express a truncated CP (tCP) with a block of N-proximal 30 residues deleted from the 66 amino acid RNA-binding domain. Subsequent biochemical characterizations revealed the presence of large ribonucleoprotein complexes that were shown to contain viral RNA as well as the approximately 38-kDa tCP. Electron microscopic examination of purified complexes showed particle-like structures that were nonuniform in size and shape compared to wild-type TBSV particles. Inoculation of pepper with the tCP-containing ribonucleoprotein complexes resulted in a rapid systemic infection similar to that caused by wild-type TBSV. In contrast, infections established in pepper by the original CP frameshift deletion mutant transcripts were restricted to inoculated leaves and did not yield recombinants capable of systemically infecting this host. In summary, TBSV possesses the flexibility to form alternative virion-like structures even if a substantial portion of the RNA-binding domain is deleted from the CP; mutants producing the tCP-containing particle-like structures are more effective for virus spread than those devoid of CP expression; and recombination events to produce the alternative tCP-RNA complexes are host-dependent.

Capsid↗

PubMed2002

A novel plant homeodomain protein interacts in a functionally relevant manner with a virus movement protein.

Tomato bushy stunt virus and its cell-to-cell movement protein (MP; P22) provide valuable tools to study trafficking of macromolecules through plants. This study shows that wild-type P22 and selected movement-defective P22 amino acid substitution mutants were equivalent for biochemical features commonly associated with MPs (i.e. RNA binding, phosphorylation, and membrane partitioning). This generated the hypothesis that their movement defect was caused by improper interaction between the P22 mutants and one or more host factors. To test this, P22 was used as bait in a yeast (Saccharomyces cerevisiae) two-hybrid screen with a tobacco (Nicotiana tabacum) cDNA library, which identified a new plant homeodomain leucine-zipper protein that reproducibly interacted with P22 but not with various control proteins. These results were confirmed with an independent in vitro binding test. An mRNA for the host protein was detected in plants, and its accumulation was enhanced upon Tomato bushy stunt virus infection of two plant species. The significance of this interaction was further demonstrated by the failure of the homeodomain protein to interact efficiently with two of the well-defined movement-deficient P22 mutants in yeast and in vitro. This is the first report, to our knowledge, that a new plant homeodomain leucine-zipper protein interacts specifically and in a functionally relevant manner with a plant virus MP.

Amino Acid Sequence↗

PubMed2002

Tomato bushy stunt virus genomic RNA accumulation is regulated by interdependent cis-acting elements within the movement protein open reading frames.

This study on Tomato bushy stunt virus identified and defined three previously unknown regulatory sequences involved in RNA accumulation that are located within the 3'-proximal nested movement protein genes p22 and p19. The first is a 16-nucleotide (nt) element termed III-A that is positioned at the very 3' end of p22 and is essential for RNA accumulation. Approximately 300 nt upstream of III-A resides an approximately 80-nt inhibitory element (IE) that is obstructive to replication only in the absence of a third regulatory element of approximately 30 nt (SUR-III) that is positioned immediately upstream of III-A. Inspection of the nucleotide sequences predicted that III-A and SUR-III can form looped hairpins. A comparison of different tombusviruses showed, in each case, conservation for potential base pairing between the two predicted hairpin-loops. Insertion of a spacer adjacent to the predicted hairpins had no or a minimal effect on RNA accumulation, whereas an insertion in the putative III-A loop abolished genomic RNA multiplication. We conclude that the sequences composing the predicted III-A and SUR-III hairpin-loops are crucial for optimal RNA accumulation and that the inhibitory effect of IE surfaces when the alleged interaction between SUR-III and III-A is disturbed.

Genes, Regulator↗