Fabien Baldacci-Cresp

New Transformation Technologies for Trees

Application of transgenic techniques to trees has emerged as a powerful tool for their genetic improvement. However, for some recalcitrant or transformation time-consuming species transgenic research should be strengthened and further efforts will be necessary to improve regeneration and transformation efficiencies. This review focuses on the recent advances and techniques for genetic manipulation that can be applied to obtain transgenic trees with enhanced biosafety. After selection of transformed plants, marker genes presence becomes useless and undesirable. For generation of marker-free transgenic plants or resolving complex transgene integration structures, several methodologies based on site-specific recombination have been developed. Precise homologous recombination-mediated integration of a DNA sequence of interest at a particular site within a genome is the ultimate tool for genetic engineering. Genome editing allows a much more precise manipulation of tree genomes. Expression of multiple transgenes is often required for engineering metabolic pathways. Recent progress has made powerful techniques available and gene stacking can be achieved in trees by two methodologies: co-transformation and serial transformation. The application of technologies based on small RNAs allowing silencing target genes (RNA interference, artificial microRNAs, and artificial trans-acting siRNAs) is of particular interest to produce directed down-regulation of target genes in tree species. Mixing of genetic materials between species that cannot hybridize by natural means is one of the major criticisms to transgenic crops. Cisgenesis and intragenesis were developed as alternatives to transgenesis.

Poplar–Root Knot Nematode Interaction: A Model for Perennial Woody Species

Plant root-knot nematode (RKN) interaction studies are performed on several host plant models. Though RKN interact with trees, no perennial woody model has been explored so far. Here, we show that poplar (Populus tremula × P. alba) grown in vitro is susceptible to Meloidogyne incognita, allowing this nematode to penetrate, to induce feeding sites, and to successfully complete its life cycle. Quantitative reverse transcription-polymerase chain reaction analysis was performed to study changes in poplar gene expression in galls compared with noninfected roots. Three genes (expansin A, histone 3.1, and asparagine synthase), selected as gall development marker genes, followed, during poplar-nematode interaction, a similar expression pattern to what was described for other plant hosts. Downregulation of four genes implicated in the monolignol biosynthesis pathway was evidenced in galls, suggesting a shift in the phenolic profile within galls developed on poplar roots. Raman microspectroscopy demonstrated that cell walls of giant cells were not lignified but mainly composed of pectin and cellulose. The data presented here suggest that RKN exercise conserved strategies to reproduce and to invade perennial plant species and that poplar is a suitable model host to study specific traits of tree-nematode interactions.

Escherichia colimazEF Toxin-Antitoxin System as a Tool to Target Cell Ablation in Plants

Background/Aims: The Escherichia coli MazF is an endoribonuclease that cleaves mRNA at ACA sequences, thereby triggering inhibition of protein synthesis. The aim of this study is to evaluate the efficiency of the mazEF toxin-antitoxin system in plants to develop biotechnological tools for targeted cell ablation. Methods: A double transformation strategy, combining expression of the mazE antitoxin gene under the control of the CaMV 35S promoter, reported to drive expression in all plant cells except within the tapetum, together with the expression of the mazF gene under the control of the TA29 tapetum-specific promoter in transgenic tobacco, was applied. Results: No transgenic TA29-mazF line could be regenerated, suggesting that the TA29 promoter is not strictly tapetum specific and that MazF is toxic for plant cells. The regenerated 35S-mazE/TA29-mazF double-transformed lines gave a unique phenotype where the tapetal cell layer was necrosed resulting in the absence of pollen. Conclusion: These results show that the E. colimazEF system can be used to induce death of specific plant cell types and can provide a new tool to plant cell ablation.

Does PtaRHE1, a poplar RING-H2 protein, play a role in water conduction through ABA signaling?

RING (REALLY INTERESTING NEW GENE) proteins with E3 ligase activity are largely represented in plants. They have been shown to play important roles in the regulation of many biological processes by recognizing target proteins for ubiquitination. PtaRHE1, encoding a poplar RING-H2 domain-containing protein with E3 ligase activity has been previously shown to be expressed during the establishment of secondary vascular system in poplar. In the present report, we demonstrate that the expression of PtaRHE1 and the accumulation of its corresponding protein are modulated by the relative atmospheric and soil humidity and by abscisic acid. Overall, the integrated data are discussed within a working model highlighting a plausible function of PtaRHE1 in the signaling and/or in the regulation of water status in poplar.