“Plant Systems Biology: integrating scales and time”
A remarkable characteristic of plants, defining part of their own existence, is the modular structure of their bodies. A module can be considered as a biological entity (an individual, a structure, a process, or a pathway) characterized by more internal than external integration. Overall, modules can be considered as the nodes of networks that are connected via the edges (different modes of short and long-distance signalling). In hierarchical systems (such as any biological multicellular organism), networks of finer scales can become nodes in networks of higher scales and so on. The response of a whole plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to modules integration. The integration among different modules is engendered by a sophisticated system of signalling spreading chemical, electrical and hydraulic information throughout the plant body. In other words, the responses of plants to their environments are emergent properties; i.e. an inevitable self-organized unfolding of new functions and structures of a system onto a higher scalar integrative level.
This internal dynamic is underpinned by complex metabolic networks subject to rules of interactions. In complex systems, such interactions are typically nonlinear processes based on negative and positive feedback loops. Negative feedback plays a crucial role in maintaining homeostasis of the system, whereas positive feedback operates by propagating and amplifying signals throughout the system. Both processes work together in the formation and stabilization of new patterns of organization, which makes the prediction of their global behaviour difficult. Such a dynamical process of organization operates throughout the different scales of the organization of the plants system, producing emergent properties non-reducible to its components at smaller scales of organization.
The understanding of such complexity has been improved by the exponential development of high-throughput technologies in the last decades, uncovering the complexity of the organizational network patterns in the cell’s metabolism to the plant phenome, thus creating the modern science of systems biology. Furthermore, the huge data sets and growing computational power have stimulated scientists to uncover how plants respond to the environmental changes, and how such knowledge could engender new technologies, for instance, to increase crop yields. Through these technologies, researchers are describing deeply the different hierarchical levels of plant organization, improving the possibility to predict the behaviour of the whole plant (phenome) based on extensive analysis of gene expression (genome and transcriptome) and/or metabolic networks (metabolome) to monitor and to manipulate cellular responses to genetic perturbation or environmental changes. However, different constrains can make this predictability difficult, challenging the bottom-up cause-effect approach that underpins the deterministic view of science based on an upward chain of causality. Thus, a main question is how to integrate, on one hand, the massive datasets from molecular high-throughput technologies and, on the other hand, the growing high-throughput information on the crop scale, i.e. plant phenomics, which is a typical problem of finding a proper general scaling law.
The importance of studying integration of different levels of biological organization relies on an ontological base: 1- spatial and temporal patterns are dependent on the scale of analysis, 2- there is more than one characteristic scale for the research, 3- experimental results cannot be directly transferred to larger scales, 4- biological interactions with the environment occur in multiple scales, and 5- environmental problems are created by the propagation of effects on different scales in the biosystem.
Therefore, the main objective of XVIII Brazilian Congress of Plant Physiology, to be held in Porto Alegre – RS in September 2021, is to expose the imbricate complexity of plants, especially when embedded in a changing environment, and to discuss the possibilities to integrate different scales of observation taking into account the temporal dynamic of the different levels of organization.