With a little help from my fungus

If you need help defending your tomato plants from pests, enlisting the help of a fungus might not be at the top of your list. But a recent study, published in New Phytologist, has shown that a fungus could actually be an unlikely ally in the greenhouse.

Similar to the beneficial microbes that inhabit the human gut, plants can play host to a range of microbes, some of which form associations with plant roots and provide their hosts with essential functions that help with nutrient acquisition and protection against pests.

Image: First author Ainhoa Martínez-Medina in the greenhouse with experimental tomato plants.
First author Ainhoa Martínez-Medina in the greenhouse with experimental tomato plants.

By using a sophisticated split-root design to test the interactions between tomato plants, a fungus of the genus Trichoderma, and the parasitic nematodes that prey on tomato plants, Dr Ainhoa Martínez-Medina and colleagues were able to show that the fungus was able to boost plant resistance to infection by increasing the production of toxic chemical compounds upon nematode attack.

“One of the main messages of this paper is that we cannot understand the interaction between plants and herbivores if we don’t consider the plant microbiome, or these beneficial associated microbes and the plant as a whole.”

Tomato plants ‘primed’ by the fungus in this way are better able to defend themselves against nematode attack, in a similar way to how vaccination helps humans to develop resistance to infection. In the future, this knowledge could help to develop solutions for sustainable agriculture.

“Beneficial microbes that live in the rhizosphere, associated with plant roots, can potentially be used to produce more food in a safer way. If we can produce inoculants to fight against pests and diseases with these beneficial microbes, that will be fantastic.”

I spoke to Dr Ainhoa Martínez-Medina about the results of her study, and her background as a plant scientist. While developing her interest in how beneficial microbes could be used as biocontrol agents against a range of diseases and pests during her PhD, under the supervision of Prof. Roldán and Prof. Pascual, at CEBAS (Centro de Edafología y Biología Aplicada del Segura) in Spain, she decided to move to the Estación Experimental del Zaidín, to work with Prof. Pozo on the transduction pathways that underlie mycorrhiza-induced resistance.

A short collaboration turned into a three year postdoc for Dr Martínez-Medina. After obtaining a Marie Curie grant, she moved to The Netherlands to join the laboratory of Prof. Pieterse, at Utrecht University, a leading group in the field of microbe-induced plant defences. Inspired by her colleagues and fascinated by the molecular and chemical mechanisms behind the influence that beneficial microbes were having on plant-herbivore interactions, it was there that she developed most of the work for this study, before moving to iDiv, in Germany.

Listen to the interview, and read the transcript below:

“My name is Ainhoa Martínez-Medina and I work as a postdoctoral researcher at iDiv, which is the German Centre for Integrative Biodiversity Research in Leipzig, and also in the Friedrich-Schiller University in Jena, in the group of Molecular Interaction Ecology, with Prof. Nicole van Dam.

“I’m mostly interested in understanding how plant-associated microbes affect how plants interact with other community members at different trophic levels. I’m particularly fascinated by how root microbes, which are living in association with plant roots, can boost plant defences, making their host plants more resistant and tolerant to pathogens and pests.

“So, I think one of the main messages of this paper is that we cannot understand how plants defend themselves against herbivores and we cannot understand the interaction between plants and herbivores, if we don’t consider the plant microbiome or these beneficial associated microbes, and the plant as a whole. It’s not only that plants that are colonised by beneficial microbes, are plants with one or two altered traits. Microbe-colonised plants are really different and so the impact that these beneficial microbes have is very deep. And then, if we consider that, in both natural and agricultural ecosystems, all the plants establish symbioses with the beneficial microbes, I think that it becomes clear that we need to incorporate the microbes and the plant microbiome when we study plant-insect interactions. I think this is a big challenge for the future and one of the main messages of this study.

Image: To study the interaction between tomato plants, the Trichoderma fungus and the nematodes, the researchers used a split-root study design (photo: Ainhoa Martínez-Medina).
To study the interaction between tomato plants, the Trichoderma fungus and the nematodes, the researchers used a split-root study design (photo: Ainhoa Martínez-Medina).

“I think one of the most exciting results of the paper is the clear phenotype. When you are doing an experiment in the greenhouse and you harvest the plants, you really see a very strong effect when the plants are colonised by beneficial microbes. It’s clear that there is something going on. More at the mechanistic level, which is what I am most interested in, this study has revealed the complexity of all these transduction pathways that are underlying this induction of defences. This boost of defences by beneficial microbes, this priming, is not a static phenomenon, it is dynamic – it adapts with the cycle of infection with these complex attackers.

“The most challenging aspect in this research is related to working at the border of two disciplines: plant-microbe interactions and plant-herbivore interactions. Merging these two disciplines into one is quite challenging.

“After realising about the complexity of these transduction pathways that are governing the induction of this resistance by beneficial microbes, I think we need to have a wider view into what is going on. I’m now working on a project that is funded by iDiv and the Friedrich-Schiller University in Jena, in which I’m trying to study those mechanisms in an untargeted way, so I’m integrating untargeted transcriptomics and also untargeted metabolomics to understand in detail what the mechanisms behind this are at different trophic levels.

“I think one of the current hot topics in general in plant science is related to the plant microbiome, because the information about the human microbiome is huge, so we are studying it a lot. But we just realised that the plants also have an associated microbiome and this is very important in how plants interact with other community members. I think this is one of the hottest questions in my research: understanding how this microbiome is affecting how plants deal with different organisms.

Image: When tomato plants are infested with nematodes, the roots form galls that are then inhabited by the little worms (photo: Ainhoa Martínez-Medina).
When tomato plants are infested with nematodes, the roots form galls that are then inhabited by the little worms (photo: Ainhoa Martínez-Medina).

“So nowadays, we know that the global population is growing very fast, and it’s clear that we need to produce more food. Despite the huge amounts of fertiliser and pesticides that we are using, the yield losses are still huge. This is a challenge for plant scientists. I think that beneficial microbes that live in the rhizosphere, associated with plant roots, can potentially be used to produce more food in a safer way. If we can produce inoculants to fight against pests and diseases with these beneficial microbes, that will be fantastic.

“I’ve had many role models during my career, but because I am a woman I would like to highlight two role models who are women. One is Prof. Pozo, because she’s really inspiring – she’s a box of ideas, and she’s very passionate. She really likes to discuss and to speak about science the whole day! The other role model is my supervisor now, Prof van Dam, because she’s not only an excellent scientist, she’s an excellent mentor. She’s really gives me room to grow up as a scientist, and I think this is very nice. But if I really think who inspired me to be a scientist, I have to think before, and I think it was the women in my family, my mother and my sister, who inspired me to be a scientist, to develop myself and to do what I wanted and whatever I believed.

“I would say I have two favourite things about my job. The first one, maybe, is the creative process. I really like that plant science and science in general allows you to be very creative, and I really enjoy developing hypotheses and analysing results, to make sense of the results and to understand what is going on. The other thing is being able to work close to other researchers in a team. Sometimes that is difficult but I think you really establish nice relationships and very good friends.

“The worst thing about being a scientist, at least in my case, is to be far away from home. Now is not the best moment for science, at least not in Spain, so that means that we have to go abroad to do science. I have been in the Netherlands for two and a half years and I have already been in Germany for two years. I don’t know when I will be able to go back to Spain. I think this is the worst thing.

“Well, one of my other secret passions is to dance. I love to dance Flamenco, although I am a very bad dancer! So even when I am abroad, in the Netherlands, or in Germany, I always try to find an academy to dance at. So now I am dancing! And that is one of my passions, beside science.”

Read the paper: Martínez-Medina, A., Fernandez, I., Lok, G. B., Pozo, M. J., Pieterse, C. M. J. and Van Wees, S. C. M. (2016), Shifting from priming of salicylic acid- to jasmonic acid-regulated defences by Trichoderma protects tomato against the root knot nematode Meloidogyne incognita. New Phytologist. doi: 10.1111/nph.14251


 

Thumbnail images: flickr/photon_de CC BY-2.0; flickr/bazzadarambler CC BY-2.0

Mike Whitfield (@mgwhitfield)
Development Coordinator
New Phytologist