Elucidating the Genetic Components of the Physiological and Metabolic Processes Governed by the TORC Regulatory Module in Poplar
Reuben Tayengwa1, Yiping Qi1, Edward Eisenstein1, Victor Busov2, Hairong Wei2, and Gary Coleman1*
1University of Maryland; and 2Michigan Technological University
The goal of this research is to identify the target of rapamycin complex-1 (TORC1)–mediated regulatory and signaling pathways and the linkage between TOR and Rho of Plants (ROP) GTPase nutrient sensing in poplar to elucidate the functional role of genes regulating nutritional responses. Through experiments using CRISPR gene editing, genomics, biochemical, and computational approaches, the project will decipher the functional significance of poplar TOR coupled to ROP GTPase nutrient sensing and signaling. This will allow the team to elucidate function and divergence in this nutrient signaling relay allowing for identification of the regulatory and signaling networks and hubs.
Understanding the genetic basis of complex physiological and metabolic traits, including resource use efficiency and abiotic stress, is necessary for improving lignocellulose crops for a sustainable biobased economy. Poplar (Populus spp.) is an important and sustainable bioenergy and bioproduct plant feedstock, yet understanding of the pathways and networks governing resource use efficiency and responses to abiotic stresses is poorly developed. Nutrient sensing and signaling is a fundamental mechanism which modulates cellular activities that mediate growth, development, and biomass accrual. The protein TOR kinase is part of an evolutionally conserved central hub that integrates not only nutrient signals but also signals related to energy, hormones, biotic, and abiotic stresses through its pivotal role in regulating transcription, translation, and metabolism. In plants, TOR signaling of diverse nitrogen signals has been linked to signal integration by ROP GTPases that modulate TOR activation and signaling outputs. Although the ROP GTPase/TOR signaling relay has been shown to be important to integrating nitrogen signals, little is known about these signaling components in poplar. Interestingly, compared to other plants species, such as Arabidopsis and rice, poplar contains two TOR genes, and researchers have discovered that the two poplar TOR genes can be gene edited to vary gene dosage resulting in viable plants with discernible phenotypes. Since in other plant species TOR knockouts or nulls are embryo lethal, researchers have a unique opportunity to employ genome editing to determine if the two poplar TOR genes have functionally diverged along with establishing the role of the TOR/ROP GTPase relay in nitrogen sensing and signaling.
The overall objective of this research is to identify the TOR-mediated regulatory and signaling pathways and the linkages between TOR and ROP GTPase nutrient sensing in poplar to elucidate the functional roles of these genes in regulating nutritional responses. Through experiments that use CRISPR gene editing, genomics, biochemical, and computational approaches, the project will decipher the functional role and divergence of the two poplar TOR genes by altering gene dosage and identifying the functional linkage between ROP GTPase signal integration and TOR activity. The specific objectives of the project are to (1) characterize carbon and nitrogen mediated TOR activation in poplar cells; (2) alter gene dosage of the two poplar TOR genes to determine their functional roles and divergence in carbon and nitrogen signaling; (3) determine which members of the small GTPase ROP gene family can integrate diverse nitrogen signals to activate TOR; (4) identify how the regulatory and signaling networks and associated regulatory factors downstream of the ROP-GTPase-TOR nutrient sensing and signaling relay have diverged; and (5) validate the function of genetic factors downstream of the ROP GTPase/TORC relay in nitrogen sensing and signaling.
The results of this project will allow the team to elucidate function and divergence in this nutrient signaling relay allowing for identification of the regulatory and signaling networks and hubs involved in nitrogen responses in poplar. Although this research is focused on nitrogen nutrition, it is likely that the results of this project will also uncover aspects of how TOR and ROP GTPases modulate other processes such as abiotic and biotic stress, and developmental processes regulating biomass yield.
This research was supported by the DOE Office of Science, Biological and Environmental Research (BER) Program, grant no. DE-SC0023011.