Part II
VM: In your opinion, what are the most significant mechanisms underlying robustness in developmental systems?
UN: Feedback is the most important mechanism. If one studies the shoot apical meristem (SAM) through the works of Meyerowitz and colleagues about how genes maintain this pool of stem cells, which forms all plant organs, it becomes clear that this is done in a feedback-dependent manner. With tweaks in the feedback module, one can see changes in the meristem’s shape and size.
Similarly, geometry and direction of growth prescribe mechanical stress patterns in a cell or a tissue. The cells/tissues resolve these stress patterns by modulating their growth through genetic crosstalk with the cell walls that experience these mechanical stress patterns. Rico and Samantha Fox nicely demonstrated this in one of their papers. In collaboration with Olivier and Daniel, we also looked at how mechanical feedback affects the genetic constitution to bring about shape and size changes.
OH: Robustness relies on redundancy, heterogeneity, incoherence, incompleteness, and randomness. To be robust, one needs to fuel inefficiencies. This is true from the molecule (e.g. Rubisco) to the ecosystem (e.g. symbioses). In plants, mechanical feedback forms the basis of robustness. Mechanical feedback mainly depends on osmotic pressure and wall properties. Thus, genes must ultimately affect these two parameters. An increasing number of articles show that this is the case. There are no tangible other ways to change the shape and growth of plants.
VM: Moving on to the next question, how do you view robustness from a philosophical standpoint?
UN: Have you read What is Life by E. Schrodinger? That book reminds us of life and science from a philosophical vantage point. It reminds me of a story. I joined Rico’s lab in January 1998 and left in December 2002, in less than five years. I spent the turn of the millennium in England. The millennium day was celebrated in Norwich. Before that millennium changed, the BBC and other channels discussed the most significant events of the last millennium. Schrodinger’s publication of What is Life was one of the most important contributions they shortlisted.
Schrodinger explains why one is so big and the other so small. We are a collection of electrons and protons; electrons and protons collect together, making an atom sequentially transform into an organ. A human is trapped in this emerging property of development, and so is a cat. This mind-boggling complexity exists, but the outcome remains stable. When one organism reaches the lowest state of energy, which is stable, it is adopted throughout evolution, and evolution uses it to achieve robustness at that particular organismal level. When discussing evolution, we often focus on time but miss space. If a stable configuration is achieved in the lowest energy state in changing space and time, the system tries to maintain and make it more robust. At the quantum level, robustness is probabilistic, but it evolves into stability at a higher level.
OH: Robustness is an inherent property of biological systems or an emergent phenomenon resulting from evolutionary processes. Evolution always selects the most robust because the long time involves many fluctuations. Life is, first and foremost, a question of robustness. Robustness builds on oscillatory behaviour (e.g. fueled by incoherent feedforward loops). Oscillations allow stability and transformability (see systems one and two from Palo Alto). This is another key of life emerging from robustness. The narrative of sober and efficient living beings has brainwashed us. I feel much better knowing that life on earth is not unreachable; it’s much closer to what we can experience daily with our bodies (which makes sense). We are robust at first order.
VM: How do you think the study of robustness will affect the interdisciplinarity of the fields?
UN: It is already interdisciplinary because robustness is present in every sphere. Robustness is present in the gene regulation arena, mechanics, etc. For example, microtubules understand growth-derived stress, which is quantifiable due to its geometry. Experts from different fields should contribute to understanding and decoding the core principles of how things operate in a biological system. Thus, in the making, it becomes an interdisciplinary process. Some time ago, we wanted to study trichome genetics and function. I had to talk to a mechanical engineer because it’s a mechanical sensor. When the rain falls, it senses the force and turns on the genes required for plant immunity, telling how interdisciplinary the system already is. I remember I had asked one of my students to map out the variance in the length/width ratio of a cotyledon, and we found a deviation in the mean population of a mutant vs WT. From what we observe, a mutation will generate variation in the shape and size of an organ and, over time, will be naturalised to its mutated form of robustness.
OH: robustness from biology can serve as a narrative to change the focus of the socio-economic world, which is still very much along the lines of key performance indicators, GDP, and other performance markers that are toxic to humans and non-humans. Robustness is getting more and more relevant as the world becomes more and more turbulent.
Mechanics is a way to link chemistry (genes) and mathematics (shape). It is necessary to make genetics more causal (otherwise, it stays correlative. It allows us to understand how molecular networks mobilise the laws of mechanics to reach different shapes. Any other method is hand waving.
VM: As we come to the last question, what role do you think plant biology will play in addressing global challenges?
UN: Plant biology has been vital in addressing global challenges. When you talk to the agronomists in India, you will see how proud they are to feed the country; it’s the same globally. The environment is changing fast and dramatically and is being affected adversely. Plants are resilient and flexible, unlike animals. They adjust and adapt, making food for us and keeping us alive. The global population is already above 7 billion, but the resources are not unlimited. We must understand that everything comes to an end, and resources need time to replenish to maintain homeostasis. We need more flexibility in our understanding to adapt our thoughts and change our habits towards conserving resources.
Grasses are often compared with resilience, flexibility, and tolerance in our scriptures, poems, and songs. Philosophically, plants can teach us how we should live. Plants teach much more than animals do themselves. Do animals learn? That is up to animals.
OH: The key to the socio-ecological crisis is not the climate; it is biodiversity and, thus, plants at first order. Fueling biodiversity and biomass is positive for resources, pollution, climate, and biodiversity. It is the most systemic lever for socio-ecological change. In practice, this means that the priority should be agriculture (agroecology, permaculture, agroforestry). If our world continues towards performance, it will become more fragile, and plants will find other ways to grow on our ruins. If we choose robustness instead, we’ll have to adjust to fluctuations, and our technologies must follow the environmental constraint (not the other way around).
VM: Thank you both very much for your time. Are there any concluding remarks that you would like to share?
UN: No! I enjoyed talking to you. Life comprises tiny moments of realisation- over time, these small insights accumulate into something profound. A Zen story beautifully illustrates this idea of gradual understanding through small realisations.
One evening, a Zen guru was returning to his shrine at the top of a hill after visiting a nearby village with his disciples. It was a stormy night, with heavy rain and thick clouds obscuring the path. The narrow trail they had to climb was perilous, with the constant danger of slipping and falling.
As they made their way up, they relied on occasional flashes of lightning to illuminate the path ahead. Each lightning strike revealed just enough of the trail for them to take a few steps forward before pausing and waiting for the next flash. Slowly but steadily, step by step, they progressed and eventually reached their destination.
When they arrived at the shrine, the guru gathered his disciples and said, “This journey you just experienced is what enlightenment is. It is a path revealed in tiny flashes—small realisations that guide you forward. Each flash clarifies the next step, and gradually, all these moments accumulate into a complete understanding.”
In life, we don’t see the entire picture at once. It’s unveiled gradually through a series of small, meaningful realisations. This is the essence of growth and enlightenment.
OH: The planet is blue, but the world is green. Learning from plants is also a life lesson.
