Pierre Coutos-Thevenot

Molecular characterization of the incompatible interaction of Vitis vinifera leaves with Pseudomonas syringae pv. pisi: Expression of genes coding for stilbene synthase and class 10 PR protein

The interaction between Vitis vinifera and Pseudomonas syringae pv. pisi was examined at the pathological and molecular levels. Leaves infiltrated with the bacterial suspension developed necrotic regions which remained restricted to the infiltrated areas. In the infiltrated zone the number of bacteria decreased around 24h after inoculation whilst no bacteria could be isolated from the non-infiltrated zone. At the molecular level, two genes, stilbene synthase (SS) and a PR10 gene, encoding putative defense proteins, were analyzed. Expression of the SS gene, measured by the analysis of transcript accumulation, was shown to be highly induced and was followed by the accumulation of resveratrol (peaking at approximately 48h post-inoculation), considered as one of the major nobreak phytolaexins in the Vitis species. We report for the first time the isolation of a genomic clone (VvPR10-1) coding for a PR10 protein from this plant. The accumulation of the corresponding mRNA (0.8kb) was observed from 3 to 96h post-inoculation, peaking at 24–48h, and was followed by the accumulation (between 24 and, at least, 96h after inoculation) of the encoded polypeptide as detected by immuno-blotting. These results indicate that our experimental system based on an interaction of the non-host plant V. vinifera leaves with P. s. pv. pisi, has to be considered as an HR-like response and is well suited for the analysis of the defense reaction of this economically important species.

Somatic embryogenesis from grapevine cells. I-Improvement of embryo development by changes in culture conditions

In conventional culture conditions without auxin, somatic embryos arising from suspension cultures of grapevine rootstock 41B (Vitis vinifera cv. Chasselas x Vitis berlandieri) are arrested at the heart stage of development. Starting from indications that inhibitors excreted in the culture medium could be responsible for this arrest, new culture conditions based on daily subculturing embryos in fresh medium have been successfully used to obtain full embryo development. From this technique, a microassay was devised for screening small amounts of extracellular molecules as potential inhibitors of embryonic development. Our results show that extracellular macromolecules of molecular weight higher than 10 kDa are likely involved in the inhibition of caulinary meristem initiation. However, other factors obviously cooperate to inhibit embryo development in conventional culture conditions

Extracellular protein patterns of grapevine cell suspensions in embryogenic and non-embryogenic situations

Abstract Somatic embryos produced from suspension cultures of grapevine rootstock 41B (Vitis vinifera cv. Chasselas × Vitis berlandieri) are blocked at the heart stage of development. Previous results have shown that extracellular macromolecules of molecular weight > 10 kDa, are likely involved in this inhibition (P. Coutos-Thevenot et al., Plant Cell Tiss. Org. Cult., 23 (1992) 125–133). The extracellular proteins and glycoproteins secreted by embryos differentiating in the absence of auxin have been compared to those secreted by undifferentiated cells growing in the presence of auxin. Specific proteins and glycoproteins (66, 62, 56, 51, 48, 36, 32, 25 and 10 kDa), under negative control of auxin, are secreted during embryogenesis. Thus, somatic embryogenesis in grapevine presents several similarities with the carrot model system as far as the influence of auxin on extracellular protein patterns and embryo differentiation is considered. This conclusion has been reinforced by showing that, as described in the carrot system, 36-kDa glycoprotein excreted by grapevine embryos is a cationic peroxidase whereas the 10-kDa protein immunoreacts with an antibody directed against a maize lipid transfer protein. Study of extracellular protein patterns of a Chardonnay CH76 cell strain, strongly affected in its embryogenic response, showed significative differences in the excretion of some specific proteins compared to the 41B cell line.

Plasma membrane transporters: a machinery for uptake of organic solutes and stress resistance

The paper gives an overview of the data concerning the plasma membrane transporters mediating the uptake of sucrose, monosaccharides, amino acids, small peptides and glutathione. Current problems and gaps are underlined, and a special focus is made on the importance of these transporters during biotic and abiotic stresses.

Influence of extracellular proteins, proteases and protease inhibitors on grapevine somatic embryogenesis

An embryogenic grapevine rootstock cell suspension, continuously grown in the presence of auxin, was predominantly composed of proembryogenic masses. When transferred to an auxin-free medium, grapevine somatic embryos developed but were rapidly blocked at the heart stage. This inhibition has been related to the presence of extracellular macromolecules (Coutos-Thévenot et al., 1992a). In this study, the initial cell population density has been found to influence markedly embryo development. Inoculations below 5·103 cells per ml were required to obtain fully grown cotyledonary embryos. Interestingly, extracellular proteins of molecular weights of 32, 34, 48 and 52 kDa accumulated in cultures grown at high population cell densities and disappeared in cultures inoculated at densities below 5·103 cells per ml. Protein fractions partially purified by ion exchange chromatography caused both an early inhibition of embryogenesis and a stimulation of secondary embryogenesis. Moreover, to test for the possibility of modulating embryo development through alterations of extracellular proteins, cultures were supplemented with proteases and protease inhibitors. The addition of trypsin increased the rate of embryo development only in cultures inoculated at a low cell population density. Conversely, the protease inhibitor aprotinin inhibited development, arresting embryos at globular and heart stages. Together, these results provide evidence that extracellular proteins modulate somatic embryogenesis and suggest that an extracellular proteolitic mechanism could be implicated in development.

Embryogenic and non-embryogenic cell lines of Daucus carota cloned from meristematic cell clusters: relation with cell ploidy determined by flow cytometry.

The presence of totipotent and non-totipotent cells in embryogenic carrot cell suspension cultures was examined by cloning of cell microclusters. Forty clones were isolated and the distribution of their embryogenic potential was studied. Nonembryogenic, weakly and highly embryogenic cell lines were selected. After one year of subculture a second cloning round showed that the highly embryogenic and the non-embryogenic cell lines were homogenous and stable. A measurement of ploidy levels of clones by flow cytometry showed that the embryogenic clones were all diploid whereas the non-embryogenic were diploid or tetraploid. Hence, for our strain, there was a strict relationship between the tetraploid state and the inability to produce somatic embryos.

Targeting the AtCWIN1 Gene to Explore the Role of Invertases in Sucrose Transport in Roots and during Botrytis cinerea Infection

Cell wall invertases (CWIN) cleave sucrose into glucose and fructose in the apoplast. CWINs are key regulators of carbon partitioning and source/sink relationships during growth, development and under biotic stresses. In this report, we monitored the expression/activity of Arabidopsis cell wall invertases in organs behaving as source, sink, or subjected to a source/sink transition after infection with the necrotrophic fungus Botrytis cinerea. We showed that organs with different source/sink status displayed differential CWIN activities, depending on carbohydrate needs or availabilities in the surrounding environment, through a transcriptional and posttranslational regulation. Loss-of-function mutation of the Arabidopsis cell wall invertase 1 gene, AtCWIN1, showed that the corresponding protein was the main contributor to the apoplastic sucrose cleaving activity in both leaves and roots. The CWIN-deficient mutant cwin1-1 exhibited a reduced capacity to actively take up external sucrose in roots, indicating that this process is mainly dependent on the sucrolytic activity of AtCWIN1. Using T-DNA and CRISPR/Cas9 mutants impaired in hexose transport, we demonstrated that external sucrose is actively absorbed in the form of hexoses by a sugar/H+ symport system involving the coordinated activity of AtCWIN1 with several Sugar Transporter Proteins (STP) of the plasma membrane, i.e., STP1 and STP13. Part of external sucrose was imported without apoplastic cleavage into cwin1-1 seedling roots, highlighting an alternative AtCWIN1-independent pathway for the assimilation of external sucrose. Accordingly, we showed that several genes encoding sucrose transporters of the plasma membrane were expressed. We also detected transcript accumulation of vacuolar invertase (VIN)-encoding genes and high VIN activities. Upon infection, AtCWIN1 was responsible for all the Botrytis-induced apoplastic invertase activity. We detected a transcriptional activation of several AtSUC and AtVIN genes accompanied with an enhanced vacuolar invertase activity, suggesting that the AtCWIN1-independent pathway is efficient upon infection. In absence of AtCWIN1, we postulate that intracellular sucrose hydrolysis is sufficient to provide intracellular hexoses to maintain sugar homeostasis in host cells and to fuel plant defenses. Finally, we demonstrated that Botrytis cinerea possesses its own functional sucrolytic machinery and hexose uptake system, and does not rely on the host apoplastic invertases.

Cloning and Cell Sorter

The ability of plant cell cultures to produce useful compounds (pharmaceutical, food additives, cosmetics) with large-scale production has been investigated by numerous authors from scientific and economical points of view. (For reviews see: Zenk and Deus 1982, Kurz and Constabel 1983, Rosevear 1984. Yamada and Hashimoto 1984, Brodelius 1985, Dougall 1985, Sahai and Knuth 1985, Collinge 1986, Fowler 1986a, Fujita and Tabata 1986, Mac Laren 1986.)