Plant Hormone Modularity and the Survival-Reproduction Trade-Off

SIMPLE SUMMARY: In this review, we explore the modularity of plant hormones and their role in the trade-off between survival and reproduction. Biological modularity refers to the organization of living organisms into distinct units that work together to ensure individual and species’ well-being. Our findings reveal that plant hormones can be classified into different modules, each with its specific function in the reproduction trade-off. The cytokinin module, for example, focuses on maximizing reproduction, while other hormone modules function to assure reproduction. Through this review, we present examples of the modular nature of plant hormones and highlight their crucial role in balancing survival and reproduction in plants. ABSTRACT: Biological modularity refers to the organization of living systems into separate functional units that interact in different combinations to promote individual well-being and species survival. Modularity provides a framework for generating and selecting variations that can lead to adaptive evolution. While the exact mechanisms underlying the evolution of modularity are still being explored, it is believed that the pressure of conflicting demands on limited resources is a primary selection force. One prominent example of conflicting demands is the trade-off between survival and reproduction. In this review, we explore the available evidence regarding the modularity of plant hormones within the context of the survival-reproduction trade-off. Our findings reveal that the cytokinin module is dedicated to maximizing reproduction, while the remaining hormone modules function to ensure reproduction. The signaling mechanisms of these hormone modules reflect their roles in this survival-reproduction trade-off. While the cytokinin response pathway exhibits a sequence of activation events that aligns with the developmental robustness expected from a hormone focused on reproduction, the remaining hormone modules employ double-negative signaling mechanisms, which reflects the necessity to prevent the excessive allocation of resources to survival.