Our group aims to understand the mechanistic and molecular basis of plant resilience with a cellular perspective using advanced light microscopy, proteomics, biochemistry, molecular biology, genetics, genomics, bioinformatics, and gene editing.

We are interested in a wide range of cellular responses that determine plant resilience to various environmental inputs, but our current main objective is to contribute solid knowledge to the biological function of the plant cell wall in response to root vascular fungi. In particular, we focus on Fusarium oxysporum, soil-borne fungi that colonize the roots of many plant species by growing through the host cell walls and devastating agricultural and natural ecosystems worldwide.

The main goal of the group in the coming years is to understand how the dynamic remodeling of root cell walls during fungal infection determines the outcome of the interaction, and to use this knowledge to reduce the infection of vascular pathogens while maintaining their ability to interact with beneficial organisms. We strongly believe that the information we gain from our work will be valuable both at a fundamental scientific level and for its societal benefits thanks to its biotechnological potential applications.

F. oxysporum colonizes roots
Confocal image showing F. oxysporum (in yellow) growing inside an Arabidopsis lateral root (celluose in blue and lignin in red). Image from Lucrezia Pinto.

More precisely, our current research lines are:

1. Study of dynamic cell wall remodeling during plant-microorganism interaction and its role in plant resilience to biotic stress.
2. Identification of the molecular basis of the ability of vascular pathogens to enter and grow in the xylem.
3. Biotechnology transfer. We will use the knowledge generated in the previous research lines to obtain genetically edited crops with greater tolerance to root stress while maintaining their capacity to interact with beneficious microbes. As proof of concept for this goal, we are focusing on oxysporum -tomato interactions

Our research in more detail

The ability of living organisms to adjust their development to the environment in which they live is key to their survival and the driving force of evolution.  In multicellular organisms, this depends on coordinating the development of its cells and maintaining homeostasis in the intercellular spaces. In plants, the compartment between the plasma membranes, called the apoplast, is largely occupied by cell walls.

Indispensable for the growth and survival of the cells and, thus, of the plant, the cell wall is strong but extensible. It is the cell face to the outside world, and counteracts the internal turgor pressure, while allowing cell expansion. Considering the wall as an integral and dynamic part of the plant cell is fundamental to understanding plant resilience.

Several studies, including those in our group, have shown that the ability of plants to regulate the properties of their cell walls is crucial for their survival in a constantly changing environment. However, the mechanisms underlying the adaptation of plants to alterations in their cell walls remain elusive, especially during biotic stress. To shed light on this fundamental biological question, our team has combined, since the lab was originally founded at the ETH Zurich in 2015, a plethora of methodologies, studying the interaction of the plant with microorganisms that live mainly in the apoplast modifying the plant cell walls: the vascular fungi Fusarium oxysporum fsps. It was on the seven-​year anniversary of this endeavor (2013), that the lab relocated to the CBGP (Madrid).

Plant cell wall and cell wall integrity signaling.
Fungus (green) growing in between root plasma membranes (magenta). Scheme of plant cell walls and its integrity signaling.

 F. oxysporum are soil-borne microorganisms that colonize the roots of many plant species. These fungi are considered pathogenic when they cause plant wilting and death, which occurs because water flow and nutrient uptake are impeded by fungal proliferation within the xylem. The essential stage of root colonization, including both infection strategies and defense mechanisms, remains poorly understood largely due to the difficulty of accessing this organ. Conveniently, one strain of F. oxysporum, Fo5176, is virulent in multiple accessions of the model plant, Arabidopsis thaliana. We have directly contributed to the establishment of this model pathosystem (Fokkens, Guo et al., 2020, G3; Menna et al., 2020, Bio-protocols; Huerta et al., 2020, Curr Protocols in Plant Bio; Menna, Dora and Sancho-Andrés et al., 2021, BMC Biol). Our work is based on the development and application of new tools that broaden the opportunities for visualize changes in the plant apoplast, plasma membrane and cell cortex at cellular resolution during plant-microbe and in response to other stresses. We combine this methodology with other technics of cell biology, proteomics, biochemistry, molecular biology, genetics, genomics, bioinformatics, and gene editing to gain insight into the plant cell wall dynamics and developmental changes during microbial infection (Kesten et al., 2019, The EMBO Journal; Gámez-Arjona et al., 2022, Science Adv; Huerta et al., 2023 Mol Plant; Kesten et al., 2023, eLife).

F. oxysporum grows through the plant apoplast to colonize the xylem.
Confocal images showing F. oxysporum (in green) growing through the apoplast of epidermal (Ep, left panel), cortex (Cx, middle panel), and pericicle (Pe, right panel) to reach the protoxylem (Px, in red in right panel). How does it go through the endodermis (En, in pink in middle panel)? Unpubished. Images from Gloria Sancho-Andres and Lucrezia Pinto

F. oxysporum contact impairs the plant cellulose synthesis machinery.
Spinning disc confocal movie of an Arabidopsis root epidermal cell co-expressing a Cellulose Synthase Subunit (CSC) fused to GFP and a Microtubule subunit (MT) fused to Td-Tomato under control condition (1/2MS, left panel) or 5 min after F. oxysporum hyphae contact (right panel). A green dashed line in the brightfield (BF) channel highlights Fo5176 hypha. From Kesten et al., 2019.

In addition, the plant-F. oxysporum study will offer solutions to the global problem of vascular pathogens, which are a major threat to agricultural and natural ecosystems worldwide. The edaphic and resistant nature of this group of pathogens and their infection strategy based on root colonization make chemical, soil management, and biological controls generally ineffective in limiting their infection. At the same time, although F. oxysporum fsps pathogenic can be devastating, most F. oxysporum strains are actually non-pathogenic, and many establish beneficial interactions with the plant, which can reduce disease caused by vascular pathogens. These non-pathogenic fungi are often confined in the outer cell layers of the root, epidermis and cortex. The ability of the fungus to reach the xylem therefore determines its pathogenicity, an ability that correlates with increased secretion of host cell wall remodeling proteins.

 

F. oxysporum devastates tomato commercial cultivars.
Images of tomato MoneyMaker cultivar 24 days after been exposed to F. oxysporum spores (bottom) or control (upper). Images from Laura Carrillo.

Our work will therefore help to understand the evolutionary differences between root-pathogen and -nonpathogen and to use this knowledge for biotechnological purposes. Noteworthy, other root vascular pathogens follow the same pathway as F. oxysporum through the root cell layers and into the xylem. In fact, several of the plant proteins involved in F. oxysporum defense have a similar function in response to bacteria root vascular pathogens (Menna et al., 2021, BMC Biol). Thus, our biotechnological approaches have the potential to increase crop resilience to various vascular pathogens.