With a Nepenthes veitchii climbing a tree (Borneo)

Plants that have stopped photosynthesizing, orchids that don’t bloom, insects whose offspring survive being eaten by a bird…


Associate Professor SUETSUGU Kenji continues to produce unique and unusual research that captures the public’s interest. He has utilized various methods to obtain these results, including field research in dark forests and minutely analysing mutualisms between species at a molecular level. He is also involved in activities to protect the habitats of important species. We interviewed Associate Professor Suetsugu about his research philosophy, which is in line with that of MINAKATA Kumagusu (1867-1941), a giant of knowledge.
 

The mystery of mycoheterotrophic plants

It seems that the scope of your research has freely expanded to encompass not only plants but also their relationships to other organisms, for example, pollinating insects.

Associate Professor Suetsugu:
Ever since I was a child, I have been interested in living things. I became a researcher because I wanted to find out about various organisms. I didn’t show any interest in toys as a young child and would observe living things instead. I also liked looking at illustrated reference books. Japanese has two phonetic lettering systems: hiragana and katakana. Although many children learn to write in the hiragana script before katakana, I learned katakana first because the names of living things were written in katakana in the books.

In early elementary school, I saw Monotropastrum humile plants for the first time on Kasugayama in Nara Prefecture. This completely white plant is unable to perform photosynthesis. At the time, I remember being amazed that such mysterious plants exist.

I am especially fascinated by symbiotic relationships; the connections between individuals of different species. This may bring to mind the image of helping each other in a friendly manner but in reality the organisms in these symbiotic relationships are fighting aggressively against each other.

Even in cases where different species appear to be helping each other, a tense battle is being played out. I am conducting research to illuminate these connections.

Tell us about the results of your research on plants that have stopped photosynthesizing.

Non-photosynthetic plants evolved from regular plants a long time ago. Actually, 90% of plant species have mutualistic relationships with fungi; photosynthetic plants give the nutrients they have acquired through photosynthesis (photosynthates) to fungi such as mushrooms or moulds, and in return they receive minerals found in the soil (such as phosphorus). This kind of relationship where both species benefit is called a mutualism, one of the categories within symbiosis. The primary factor in maintaining such mutualisms is that both species evaluate the exchange to make sure that it benefits them. For example, if a fungus no longer receives photosynthates, it can usually stop giving the plant minerals. However, mycoheterotrophic plants have stopped performing photosynthesis and feed off fungi, thus betraying their supplier of minerals. I am investigating the mechanism by which these plants ‘cheat’ to obtain nutrients.

Associate Professor Suetsugu holding cultured seedlings of the rootless and leafless plant Cymbidium macrorhizon

The importance of conducting micro-level analyses

It’s necessary to conduct both observations in the field and analyses in the laboratory, isn’t it?

Photosynthesis is part of plants’ identity, so I am interested in how and to what degree mycoheterotrophic plants change to stop performing this process. Mycoheterotrophic plants are able to live in completely dark environments where normal plants can’t survive, and this changes their relationships with other living things, so it is important to observe their form and way of living with your own eyes. At the same time, because the mycorrhizal network that stretches underground cannot be seen with the naked eye, it is necessary to investigate these plants on a DNA level to understand what kind of relationship they form with fungi underground. With recent advances in research methodologies, the divide between macrobiology and microbiology is becoming smaller, so it is now also possible for field researchers like me to conduct studies on a genome level (eg. gene expression analysis). I would like to continue to incorporate new research methodologies while seeking the answers to challenging questions.

Stick insects look like the branches of a tree, and your research has revealed that even if they are eaten by a bird, their offspring can survive. Are you currently researching insects as well as plants?

Stick insect eggs resemble plant seeds in appearance, and like plant seeds, they are also tough. Within fruit-bearing plants, there are many species in which if the fruit is consumed by a bird, the flesh of the fruit is digested but the seeds within it remain. The seeds are then expelled from the bird in its excrement in a place far away from the parent plant and can germinate. I hypothesized that the same thing happens with stick insect eggs and investigated this. This discovery overturned the common belief that when insects are eaten by birds, they lose their chance of survival, along with their offspring, but as a scientist who mainly studies plants, I came up with this idea.

Even though stick insects themselves cannot fly, when we consider the results from the genetic analyses that I am currently conducting with co-researchers, it is highly possible that having their eggs carried by the birds that consume them contributes to increasing the distribution of the stick insect population. Of course, this doesn’t mean that individual stick insects are happy to be eaten by birds. However, the upshot of this is that the species are distributed to distant areas where an individual insect could not walk. I think I have shown that from different viewpoints, even relationships that seem harmful at first glance can have beneficial effects on a species in the long-term.

Monotropastrum humile feeding on mushrooms

The mycoheterotrophic plant Sciaphila yakushimensis

Collaborating with independent researchers

Associate Professor Suetsugu conducting an ecological survey of Monotropastrum humile in Kirishima

Your network of unaffiliated botanists, enthusiasts and photographers is linked to your research achievements, isn’t it?

There are enthusiastic amateurs who set up websites to publish photos of unusual plants. I contacted such a person during my student days when I had yet to publish many papers. They were wary at first since it is necessary to avoid giving out information about rare species. However, we gradually built up mutual trust by going to the field together. Now many people contact me to tell me about different unusual plants. Even my core collaborators, who possess a research-oriented outlook and have worked with me to illuminate phenomena as joint researchers, number in the dozens. Thanks to the support of these independent specialists, we have been able to conduct research smoothly.

To protect endangered species in places like Yakushima, you are working with local residents to raise awareness of these habitats’ importance.

Yakushima has a wide range of elevations, from low coastline areas to its highest mountain peak around 2000m above sea level. Therefore, this islands diverse climates are fascinating to biologists. However, apart from the area where cedars over 1000 years old grow (such as the Jomon cedar), many other vital places on Yakushima are outside the natural world heritage and national park boundaries. I am involved in the conservation of unprotected lowland forests. I discovered that this area is an essential habitat for a species of mycoheterotrophic plant that doesn’t grow anywhere else, which is a rare occurrence. However, logging is being carried out in the surrounding forest, which means that wind blowing through the protected area and damaging these important species is, unfortunately, an everyday occurrence. As researchers, we should point out the importance of these kinds of habitats and aid conservation efforts.

Contributing to nature conservation like Minakata Kumagusu (1867-1941)

Shrine forests are areas of forest around some Shinto shrines that people don’t enter, thus providing a valuable habitat for important species. Like the pioneering biologist, naturalist and ethnologist Minakata Kumagusu, who fought to protect shrine forests in the early 20th century, Associate Professor Suetsugu is also involved in conservation efforts.

Associate Professor Suetsugu: Most people don’t pay much attention to mycoheterotrophic plants and slime moulds but Minakata Kumagusu conducted extensive research on them. He had the foresight to call for the protection of shrine forests, which provide critical habitats for these organisms. In this way, I feel that my research philosophy is compatible with that of Minakata. Actually, when I was in kindergarten, I was told that I resembled Minakata Kumagusu, probably because I would observe living things instead of playing in a group with the other children.

I would like to illuminate the mysterious aspects of various organisms. As Minakata did, I would like to solve the riddle of mysterious phenomena without limiting myself to a particular subject.

Taking advantage of Japan’s biodiversity, I would like to look into the unimaginable worlds of such living things, and conduct research that makes people go ‘Really? Wow!’. In particular, I plan to thoroughly investigate non-photosynthesizing plants across the boundaries between macrobiology and microbiology.

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