Low doses of toxic chemicals have often been shown to enhance the biological performance of organisms. This phenomenon, which has been termed hormesis, seems to be based on compensatory processes following an initial disruption of cellular functions. Hormesis may thereby enable organisms to adjust to sudden environmental changes. Although hormetic phenomena have been described for a wide variety of organisms and stimuli, only few studies have addressed details of the biological basis of hormesis and it is unclear, if distinct forms of hormesis are mediated by common genetic processes. Biological mechanisms underlying hormesis in plants are completely unknown and have never been systematically analyzed. This project utilizes Arabidopsis, the most advanced experimental plant system, to initiate detailed studies on the genetics of plant hormesis. The main goal of this initial project phase will be to establish unequivocal evidence for hormesis in Arabidopsis and to provide preliminary insights on the types of biological processes that mediate these hormetic responses. Following the identification of disparate agents potently inducing hormesis in Arabidopsis, mutants of this species with defects in genes involved the control of hormesis will be identified and characterized. This will allow researchers to uncover genes critical for plant hormesis and will reveal if distinct types of hormesis are controlled by common or distinct processes. These results will provide a foundation for future expanded studies on plant hormesis and its relevance for hormesis in other types of organisms. This project is likely to impact medical research and will serve as a basis for future approaches utilizing hormesis for enhanced crop production. The project will provide training to graduate students as well as undergraduate students, mainly from minority groups that are underrepresented in the sciences. This study will be linked to classes on plant biochemistry and genetics taught for undergraduate and graduate students.
" PI: Thomas Eulgem University of California at Riverside Federal Award ID: 1313814 Low doses of toxic chemicals have often been shown to enhance the biological performance of organisms. This phenomenon, which has been termed hormesis, seems to be based on compensatory processes following an initial disruption of cellular functions. Hormesis may thereby enable organisms to adjust to sudden environmental changes. Although hormetic phenomena have been described for a wide variety of organisms and stimuli, only few studies have addressed details of the biological basis of hormesis and it is unclear, if distinct forms of hormesis are mediated by common genetic processes. Biological mechanisms underlying hormesis in plants are completely unknown and have never been systematically analyzed. This project utilizes Arabidopsis, the most advanced experimental plant system, to initiate detailed studies on the genetics of plant hormesis. The main goal of this initial project phase was to establish evidence for hormesis in Arabidopsis and to provide preliminary insights on the types of biological processes that mediate these hormetic responses. Starting point of this NSF-funded EAGER project was the observation that low doses of synthetic plant defense elicitors trigger strong hormetic effects in Arabidopsis resulting in enhanced growth of roots, while high doses of these compounds inhibit root growth. Synthetic elicitors are drug-like compounds that activate plant immune responses and are structurally distinct from natural plant defense inducers. By high throughput screening the PI’s lab previously identified 114 new synthetic elicitors that trigger immune responses in Arabidopsis. The novel synthetic elicitor HTC was found to particularly strongly enhance Arabidopsis root growth when applied at low doses. New results from this exploratory study now suggest that hormetic effects triggered by synthetic elicitors in Arabidopsis roots are caused by enhanced expression of root-development specific genes and suppression of basic energy metabolism in aerial plant parts. Perception of low synthetic elicitor doses triggers a highly coordinated inter-compartmental gene expression response manifested in suppression of photosynthesis- and respiration-related genes in the nucleus, chloroplasts and mitochondria as well as induction of root-development-related nuclear genes. Furthermore, two genes known to be involved in the perception of the plant hormone auxin were found to serve as critical regulators of hormetic responses in roots. Results from this study are interesting for three reasons: (1) they provide a mechanistic/physiological explanation for the observed hormetic effects; (2) they point to an unknown link between defense processes and root development; (3) the observed multi-compartmental transcriptional response points to a novel type of regulatory mechanism coordinating responses in the nucleus, chloroplast and mitochondria. These results will provide a foundation for future expanded studies on plant hormesis and its relevance for hormesis in other types of organisms. This project is likely to impact medical research and will serve as a basis for future approaches utilizing hormesis for enhanced crop production. The project provided extensive training to a graduate student as well as two undergraduate students, one from a minority group that is underrepresented in the sciences. Results and concepts from this study were incorporated in a class on plant biochemistry the PI annually teaches for advanced undergraduate student at UC-Riverside.
