There are many situations in a plant’s life when self-destruction of some cells is required. This may happen to create empty spaces inside tissues or when energy needs recycling for new growth or when a scorched earth policy is required to stop the progression of a pathogen. These situations occur during e.g. the germination of seeds, the differentiation of vascular elements, the reproduction and the senescence of plants and under pathogen attack. In all cases, a precise and spatially confined activation of cell death is required and can only been achieved by a complex genetic control. Genetically controlled self-destruction of a cell is termed Programmed Cell Death (PCD). The process of PCD in plants is unlikely to mirror what has been described in animal and is likely to represent a novel alternative pathway to be discovered. In particular, major animal regulators such as the Bcl2 family and the caspase family are absent from plants genomes. Unravelling the molecular mechanism of plant PCD has implications for the understanding of PCD evolution in eukaryotes and for biotech applications in plants and algae. The research in my laboratory is entirely focussed on discovering the network of the core components of PCD in plants.

Programmed Cell Death in Plants

Programmed Cell Death in Plants using A. thaliana

Programmed Cell Death (PCD) plays a key role in defence and development of all multicellular organisms. Plants are no exception and use PCD at several stages of their life cycle. Because of this, manipulating PCD is a target for crop improvement and crop protection. 
We are combining cell biology, genetics, biochemistry, transcriptomics and proteomics to unravel novel regulators and organise what is already known into a coherent network. We discovered a short peptide that belongs to a totally novel regulator family and identified proteases that are required for PCD progression. Ultimately we need to position those regulators in an organised network in collaboration with other labs.

Kiss Of Death, a short peptide inducing Programmed Cell Death

KISS OF DEATH (KOD) is a 25-amino-acid peptide, with an alpha helix, that activates PCD in Arabidopsis thaliana. Its expression varies during development and is induced by abiotic stress and during the hypersensitive response to pathogens. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced cell death of root hairs after a 55°C heat shock. Furthermore, dexamethasone-induced KOD expression was sufficient to depolarize the mitochondrial membrane and activate caspase-like activities, causing cell death. The PCD suppressor genes AtBax-inhibitor1 repressed this cell death. We believe KOD fits in the early steps of plant PCD and we are keen to unravel the pathway that KOD activates by identifying targets for this peptide.

Metacaspases and caspase-like proteases

Metacaspases and PCD

Arabidopsis metacaspase-8 (MTC8) modulates PCD induced by UV or H2O2. We published evidence that metacaspase-8 is one of the nine family members that is required for the completion of PCD induced by UV or H2O2. Enzymatic assays using recombinant MTC 8 showed that it had no caspase activity despite its name. This observation is contrary to early suggestions based on indirect evidence that metacaspases were responsible for the caspase-like activities detected in plants. Metacaspases are generally believed to act upstream of caspase-like activities, possibly activating the proteases involved. We need to work out the mode of action of metacaspase 8, where is it localised, what does it activate or inactivate.

Caspase3-like proteases
There is no caspase3 gene in plants but there are proteases that can cleave caspase3 in vitro substrate and that are required for PCD. After many optimisation steps, purification and MS/MS identified a cysteine protease from seedlings that has caspase3 activity. Following this breakthrough, we are analysing the targeting of this protease to the vacuole (see fig) and try to position it in the PCD pathway .

Microalgae and Biofuels

Developing the use of plants or algae as a sustainable source of biofuels is highly desirable. This approach however faces major challenges to avoid biofuel competing with food production and to bring the production cost down. 

• Plants for the future (2nd Year)

• Green Biotechnology (3rd Year)

• Erasmus coordinator and Degree-with-language placement abroad