Meet Sylvain Merlot, laureate of a TULIP package

What is your background ?

I started with a thesis at the Institut des Sciences du Végétal in Gif-sur-Yvette, on abscisic acid (ABA) signalling in Arabidopsis thaliana, afterwards, I did a 4-year postdoc at the University of San Diego working on chemotaxis in the amoeba dictyostelium.

At the end of 2004 I was recruited at the CNRS where I returned to the subject of my thesis but focused my research on the protein kinases and phosphatases involved in the ABA signalling pathway.

After 5 years, I decided to change my research topic and started working on metal hyperaccumulation in plants. To initiate this new project, I spent 2 years in New Caledonia on secondment from the IRD before returning to the I2BC in 2011.

What is your research about?

Metal hyperaccumulating plants are quite particular plants that grow on soils rich in metals that are toxic for most plants. There are some in France, but one of the main regions is New Caledonia in terms of species diversity, thus explaining the initiation of my projects there.

The soils of New Caledonia are ultramafic soils, very poor in nutrients and rich in iron oxide, nickel, chrome, manganese and magnesium. It should be noted that there are essential metals (such as iron, manganese, etc.) and non-essential metals (such as cadmium).

In soils where metals are in excess, most species tend to exclude these metals. Hyperaccumulation is therefore a rare occurrence because it is probably energy-consuming to accumulate something against gradients and also to synthesise molecules to chelate metals and limit their toxicity. So if we do not imagine a positive selection system, this mechanism should not be selected.

Several theories :

• allelopathy : when the leaves of the accumulator plants fall, this creates an even more metal-enriched environment in the vicinity and thus limits competition with other species
• defence against insects: by having toxic leaves, to protect against insects, even if there have been co-evolutions and some insects have adapted very well and eat hyper-accumulative plants
• the defence response against pathogens: fungi or bacteria. And there is more data that supports this theory.

My goal is to identify the genes or loci involved in metal hyperaccumulation. These genes problably evolved from genes involved in the regulation of metal homeostasis that is essential for all plant species. Hyperaccumulation is likely linked to major changes in the expression and/or activity of some of these genes.

Euphorbia helenae (Mayari, Cuba) with a bluish nickel-rich latex
Credit : Sylvain Merlot

What axis of research will you explore ?

What is interesting in my project is both to understand original molecular mechanisms and to study their diversity. There are about 700 metal hyperaccumulating species, the large majority accumulates nickel. I'm therefore trying to find out if nickel hyperaccumulators from distinct families share similar mechanisms or if there are specificities. I'm also trying to understand if some mechanisms involved in nickel hyperaccumulation are also important for the accumulation of other metals and what are the specific mechanisms for each metal.

I previously worked on hyperaccumulators from different families such as Rubiaceae and Euphorbiaceae, through my collaborations in New Caledonia and Cuba. 

My project is now essencially based on Noccaea caerulescens, from the Brassicaceae family, which is able to accumulate zinc, nickel and cadmium. Zinc and cadmium are often linked for molecular reasons, but it is quite rare that the same species is able to accumulate both nickel and zinc.

Noccaea caerulescens (Firmi, Aveyron)
Credit : Sylvain Merlot

Why join the LRSV and TULIP ?

I think my project will benefits from its integration into the LRSV and the TULIP LabEx, both favoring researches at the Biology and Environment interface.

Finally, the Occitanie region has a great mining history, in Ariège, towards Montpellier, in Tarn and in Aveyron, on different types of soil rich in metals including zinc or nickel. This is a hotspot of diversification for Noccaea caerulescens. I previously perfomed prospections of N. caerulescens in the region and I hope the geographical proximity with Toulouse will facilitate my access to this species to study its diversity from the genomic to the environmental levels.

How will the TULIP package help you ?

This was essential ! I was interested to come to the LRSV to further develop my projects on metal hyperaccumulation in Noccaea, but it is relatively difficult to move from a laboratory to a distant one. Without the TULIP package I would not have been able to transfer my activity here. It gives me the opportunity to restart my project here with good conditions. A large part of the package will be used to recruit a PhD student, and part will be invested in genomics. The presence of the Genotoul platform at the INRAE Occitanie-Toulouse centre, was also important in my decision to come.

To summarise your upcoming projects

Develop Noccaea caerulescens as a model species for metal hyperccumulation :

• Prospecting for new accessions to study the diversity and evolution of hyperaccumulation
• Genomic studies to identify genetic variations linked to metal hyperaccumulation in different accessions to target candidate genes
• The development of transgenesis in this species, that is relatively recalcitrant, is essential to demonstrate and understand the role of genes involved in metal hyperaccumulation.