Regulation of growth defense tradeoffs by temperature.

Plants must grow fast enough to compete with their neighbors, while maintaining appropriate defenses against pathogens. Because defending and growing are costly processes, the survival of the more than 300,000 species of plants that currently inhabit earth often requires crosstalk between the two. Since the decision to grow or to defend depends on information derived from the local environment, plants must sense and respond to their environment in a coordinated way. For instance, temperature elevation can affect both growth and defenses in plants. The overall goal of this project is to understand how temperature signals affect defense and growth responses. For this, we study the signaling pathway controlled by Brassinosteroids (BRs), the steroids of plants. The BR signaling pathway is one of the very few systems in which the tools and mechanistic details exist to study cross talk at the molecular level. BRs can promote or interfere with plant growth and defenses, and the regulation of this crosstalk by temperature is largely uncharacterized. The specific goal of the proposed research is to use Arabidopsis thaliana as a model system to understand how the BR signaling pathway helps plants regulate growth and defense decisions when temperature is changing. To address this, we will use genomic, molecular genetics, biochemistry and cell biology methods. One of the major challenges of plant research in the 21st century is to breed crops that are resilient to global warming while displaying broad-spectrum and durable resistance to pathogens. Understanding how plants grow and defend themselves in elevated temperature conditions could provide a conceptual framework for developing promising biotechnological tools that would afford realistic prospects for developing plants with sustainable resistance to unrelated phytopathogens in the context of global warming.

Plants must grow fast enough to compete with their neighbors, while surviving in the presence of pathogens. Rather than stopping their growth to defend themselves, plants often strike a balance between defense and growth, satisfying simultaneous, yet metabolically conflicting demands. To regulate the flux of available resources towards growth or defense programs, plants monitor their environment for specific signals and transduce them into complex molecular responses. There is very limited knowledge of how environmental cues help plants regulate the effective use of costly, but beneficial, investments towards defense at the detriment of growth processes. For instance, attenuated plant immune responses to some pathogens have long been observed at high temperatures in above ground tissues. There is also mounting evidence that the outcome of a plant-pathogen interaction can be modulated via growth-promoting hormones such as Brassinosteroids (plant steroids; hereafter referred to as BRs). While the mechanisms by which temperature and growth-promoting hormones impact disease or resistance are starting to emerge, there is still very limited knowledge of how plant immune responses are layered atop temperature and BR response programs. Understanding the intersection between growth and defense pathways in plants is a century-old question, empirically formulated as the "dilemma of plants". A better understanding of the major components and hierarchical structure of the signaling networks that affect the plant dilemma between "growth" and "defense" would benefit both: (i) Fundamental research scientists aiming at understanding the regulatory mechanisms that plants use to integrate the perception of a particular pathogen while undergoing dynamic and coordinated developmental changes (ii) Applied research scientists, because the mechanisms that regulate growth defense tradeoffs can ultimately help to influence biomass quality and quantity in agricultural crops.