Regulatory Features Underlying Pollination-Dependent and -Independent Tomato Fruit Set Revealed by Transcript and Primary Metabolite Profiling

Indole Acetic Acid 9 (IAA9) is a negative auxin response regulator belonging to the Aux/IAA transcription factor gene family whose downregulation triggers fruit set before pollination, thus giving rise to parthenocarpy. In situ hybridization experiments revealed that a tissue-specific gradient of IAA9 expression is established during flower development, the release of which upon pollination triggers the initiation of fruit development. Comparative transcriptome and targeted metabolome analysis uncovered important features of the molecular events underlying pollination-induced and pollination-independent fruit set. Comprehensive transcriptomic profiling identified a high number of genescommonto both types of fruit set,amongwhich only a small subset are dependent on IAA9 regulation. The fine-tuning of Aux/IAA and ARF genes and the downregulation of TAG1 and TAGL6 MADS box genes are instrumental in triggering the fruit set program. Auxin and ethylene emerged as the most active signaling hormones involved in the flower-to-fruit transition. However, while these hormones affected only a small number of transcriptional events, dramatic shifts were observed at the metabolic and developmental levels. The activation of photosynthesis and sucrose metabolism-related genes is an integral regulatory component of fruit set process. The combined results allow a far greater comprehension of the regulatory and metabolic events controlling early fruit development both in the presence and absence of pollination/fertilization

RNA editing in plant mitochondria, cytoplasmic male sterility and plant breeding

RNA editing in plant mitochondria is a post-transcriptional process involving the partial change of C residues into U. These C to U changes lead to the synthesis of proteins with an amino acid sequence different to that predicted from the gene. Proteins produced from edited mRNAs are more similar to those from organisms where this process is absent. This biochemical process involves cytidine deamination. The cytoplasmic male sterility (CMS) phenotype generated by the incompatibility between the nuclear and the mitochondrial genomes is an important agronomical trait which prevents inbreeding and favors hybrid production. The hypothesis that RNA editing leads to functional proteins has been proposed. This hypothesis was tested by constructing transgenic plants expressing a mitochondrial protein translated from unedited mRNA. The transgenic "unedited" protein was addressed to the mitochondria leading to the appearance of mitochondrial dysfunction and generating the male sterile phenotype in transgenic tobacco plants. Male sterile plants were also obtained by expressing specifically a bacterial ribonuclease in the anthers. The economical benefits of artificially engineered male-sterile plants or carrying the (native) spontaneous CMS phenotype, implies the restoration to obtain fertile hybrids that will be used in agriculture. Restoration to fertility of transgenic plants was obtained either by crossing male-sterile plants carrying the "unedited" mRNA with plants carrying the same RNA, but in the antisense orientation or, in the case of plants expresing the ribonuclease, by crossing male-sterile plants with plants expressing an inhibitor specific of this enzyme

A specific Gibberellin 20-oxidase dictates the flowering-runnering decision in diploid strawberry

Asexual and sexual reproduction occur jointly in many angiosperms. Stolons (elongated stems) are used for asexual reproduction in the crop species potato (Solanum tuberosum) and strawberry (Fragaria spp), where they produce tubers and clonal plants, respectively. In strawberry, stolon production is essential for vegetative propagation at the expense of fruit yield, but the underlying molecular mechanisms are unknown. Here, we show that the stolon deficiency trait of the runnerless (r) natural mutant in woodland diploid strawberry (Fragaria vesca) is due to a deletion in the active site of a gibberellin 20-oxidase (GA20ox) gene, which is expressed primarily in the axillary meristem dome and primordia and in developing stolons. This mutation, which is found in all r mutants, goes back more than three centuries. When FveGA20ox4 is mutated, axillary meristems remain dormant or produce secondary shoots terminated by inflorescences, thus increasing the number of inflorescences in the plant. The application of bioactive gibberellin (GA) restored the runnering phenotype in the r mutant, indicating that GA biosynthesis in the axillary meristem is essential for inducing stolon differentiation. The possibility of regulating the runnering-flowering decision in strawberry via FveGA20ox4 provides a path for improving productivity in strawberry by controlling the trade-off between sexual reproduction and vegetative propagation

Caractérisation de l'interaction des protéines IMA/MIF2 et CSN5 au niveau moléculaire et physiologique

Les plantes ont la capacité à former de nouveaux organes grâce à une croissance continue assurée par une réserve de cellules souches au sein de structures spécifiques, les méristèmes. Les méristèmes floraux diffèrent des méristèmes végétatifs par leur caractère déterminé aboutissant à la production des fleurs. Le gène IMA (INHIBITOR OF MERISTEM ACTIVITY) code une protéine contenant un motif doigt à zinc (MIF) régulant les processus développementaux de la fleur et des ovules chez la tomate. En effet, IMA inhibe la prolifération cellulaire au cours de la terminaison florale en agissant sur l expression du gène WUSCHEL, responsable du maintien du pool de cellules souches et contrôle le nombre de carpelles (Sicard et al., 2008). De plus, les protéines IMA et son orthologue chez Arabidopsis, MIF2, modulent la réponse à certaines phytohormones. De manière identique à la protéine MIF1 (Hu and Ma, 2006), IMA/MIF2 régule négativement la réponse aux brassinostéroïdes, à l auxine, aux cytokinines et aux gibbérellines mais positivement la réponse à l acide abscissique suggérant une fonction commune des protéines MIF dans les voies de réponse aux phytohormones. Un criblage d une banque d ADNc par la technique de double hybride a permis de révéler l interaction entre les protéines IMA/MIF2 et une sous-unité du complexe signalosome, CSN5. De façon intéressante, les plantes mutantes csn5 d Arabidopsis montrent de nombreuses altérations phénotypiques telles qu un aspect buissonnant résultant de la perte de la dominance apicale, et une altération de la réponse à l obscurité et à l auxine. Ces phénotypes sont fortement ressemblants aux phénotypes des plantes MIF1OE d Arabidopsis (Hu and Ma, 2006) et des plantes IMAOE de tomate (Sicard et al., 2008). Les résultats obtenus au cours de ce projet montrent que la protéine IMA inhibe la fonction du complexe signalosome grâce à son interaction avec la protéine CSN5.Plants have the ability to form new organs as a result of indeterminate growth ensured by specific regions of pluripotent cells, called meristems. Flowers are produced by the activity of floral meristems which differ from vegetative meristems in their determinate fate. The INHIBITOR OF MERISTEM ACTIVITY (IMA) gene encoding a Mini Zinc Finger (MIF) protein from tomato (Solanum lycopersicum) regulates the processes of flower and ovule development. IMA inhibits cell proliferation during floral termination, controls the number of carpels during floral development and acts as a repressor of the meristem organizing centre gene WUSCHEL (Sicard et al., 2008). We demonstrated that IMA and its Arabidopsis ortholog MIF2 is also involved in a multiple hormonal signalling pathway, as a putative conserved feature for plant MIF proteins (Hu and Ma, 2006). Alike Arabidopsis MIF1, IMA/MIF2 regulates negatively BR, auxin, cytokinin and gibberellin signalling and positively ABA signaling. Using yeast two-hybrid screening experiments, we identified a strong protein-protein interaction between IMA and the signalosome subunit 5 (CSN5). Interestingly the csn5 mutant in Arabidopsis displays pleiotropic developmental defects such as a bushy phenotype originating from the loss of apical dominance and the alteration in sensitivity to darkness and auxin signals. These phenotypes are strikingly similar to what was described for Arabidopsis MIF1 (Hu and Ma, 2006) and tomato IMA overexpressors plants (Sicard et al., 2008), respectively. Taken together our data strongly suggest that IMA may act as an inhibitor of CSN function through its physical interaction with SlCSN5. The observed converse effects of IMA/MIF2 overexpression or deregulation on plant development and the abundance of developmental marker genes further support the notion of a CSN inhibitory control, since the COP9 signalosome through the specific deneddylation activity of the CSN5 subunit regulates plant hormone signalling.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Caractérisation moléculaire des anomalies du développement floral chez la tomate infectée par le phytoplasme du Stolbur

National audienc

Characterization of the balance between asexual and sexual reproduction in diploid strawberry

Characterization of the balance between asexual and sexual reproduction in diploid strawberry. Plant Biology Scandinavia 2015, The 26th SPPS Congres

Caractérisation moléculaire des anomalies du développement floral chez la tomate infectée par le phytoplasme du Stolbur

National audienc

Characterization of the balance between asexual and sexual reproduction in diploid strawberry

Characterization of the balance between asexual and sexual reproduction in diploid strawberry. Plant Biology Scandinavia 2015, The 26th SPPS Congres