Metabolic Regulation of Plant Growth
The research group of Dr Camila Caldana aims at understanding the regulatory mechanisms of plant metabolism to promote growth in response to energetic status/environmental signals. In particular, we are interested in dissecting the role of the Target Of Rapamycin (TOR) pathway, a central regulator coordinating those factors among eukaryotes. We use Arabidopsis thaliana as a model system to decipher the basis mechanism, but we are extending our knowledge to fast-growing species such as Setaria viridis and the crop sugarcane.
Plant growth results from a combined action among metabolism, availability of environmental resources (i.e., water, nutrients and light), and cellular and developmental programs. Apart from being energy suppliers and macromolecule building blocks, carbon (C) and nitrogen (N) status can be perceived as metabolic inputs by energy-sensing regulators that control how, when and where resources are utilized, coordinating plant metabolism and growth. Although the control of resource allocation in plants is still poorly understood. Our research aims at identifying and understanding these regulatory mechanisms as means to improve plant performance by using the following approaches:
1. Elucidation of the role of the TOR pathway in energy sensing and management to promote plant growth
One of the key components in integrating environmental signals to growth decisions is the well-conserved kinase Target Of Rapamycin (TOR). We previously showed that the TOR kinase affects a plethora of metabolic pathways integrating energy status and carbon partitioning into growth (Caldana et al., 2013, Jueppner et al., 2017). Due to the centrality of this pathway in controlling a range of biological processes (Dobrenel et al., 2016), our group has undertaken a combination of molecular genetics, biochemical and physiological analyses, identification of protein‒protein/protein‒metabolite complexes, metabolomics and data integration to unravel direct targets of the TOR pathway and their physiological functions.
We have identified a possible involvement of the TOR pathway in adjusting C balance, more specifically the partitioning between sucrose and starch, in order to match growth demand. Similarly to sugars, nitrogen (N) nutrient and signals can act as signals affecting plant growth and development. We are extending our knowledge by further exploring the key players/pathways involved in this network as well as its connection to other energy sensing pathways.
Although, evolutionary studies have suggested that the core of this complex is conserved among eukaryotes, new regulatory steps and outputs have been added during evolution to match the needs in multicellular or autotrophic environments. We aim at unravelling the conserved and species-specific modes of the TOR interactome by employing PROMIS (Veyel et al., 2017) using yeast, HeLa cells and Arabidopsis.
2. The use of genetic diversity for the unbiased identification of novel factors controlling metabolism and plant growth/biomass
During the last years, we have started to explore the genetic factors controlling metabolic and plant biomass traits to elucidate their relationships, using sugarcane as a model. Apart from being a sustainable crop with respect to C efficiency and bio-energetic yield per hectare, sugarcane is used as feedstock for a range of products (e.g. ethanol, sugar, polymers and bioelectricity), representing a remarkable biomass source. A current change in paradigm in sugarcane breeding programs aims to alter the balance of C partitioning to facilitate the acquisition of high-value products. The so-called energy cane has higher biomass production rather than sucrose content. We have been taking the advantage of sugarcane accessions to unravel novel players in this process. Based on our preliminary results in Arabidopsis, we have hypothesized that a precise TOR activity is required for fine-tuned regulation of C partitioning for optimizing growth. We will also use this genetic resource in a targeted manner to associate polymorphisms in the genes encoding for components of the TOR pathway with starch and sucrose content, and growth and biomass parameters.
Caldana C, Li Y, Leisse A, Zhang Y, Bartholomaeus L, Fernie AR, Willmitzer L, Giavalisco P. 2013. Systemic analysis of inducible target of rapamycin mutants reveal a general metabolic switch controlling growth in Arabidopsis thaliana. Plant J. 73(6):897-909
Dobrenel T, Caldana C, Hanson J, Robaglia C, Vincentz M, Veit B, Meyer C. 2016a. TOR Signaling and Nutrient Sensing. Annual Review of Plant Biology 67: 261–285.
Jüppner J, Mubeen U, Leisse A, Caldana C, Wiszniewski A, Steinhauser D, Giavalisco P 2018. The target of rapamycin kinase affects biomass accumulation and cell cycle progression by altering carbon/nitrogen balance in synchronized Chlamydomonas reinhardtii cells. Plant J.,93(2):355-376.