Author ORCID Identifier

https://orcid.org/0000-0003-0993-3950

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Plant and Soil Sciences

First Advisor

Dr. Jan Smalle

Abstract

Cytokinin, long known as a phytohormone that regulates plant growth and development, has been recently recognized as an important regulator of stress responses. However, our current knowledge about the mechanisms by which cytokinin regulates stress responses is fragmentary, as many of the studies in this field yielded conflicting results. Most of the work described here has focused on analyses of the molecular mechanisms of cytokinin-dependent regulation of growth and development under stress conditions, with an emphasis on the role of cytokinin-dependent regulation of protein synthesis in development and stress tolerance.

One of the important contributions of this study is the finding that cytokinin- dependent induction of protein synthesis requires both the canonical cytokinin signaling pathway and isoforms RPL4A and RPL4D of the RIBOSOMAL PROTEIN L4. Further analyses investigated the role of the cytokinin-dependent increase in protein synthesis in stress responses, and this research underlined the importance of balanced regulation of cytokinin-induced protein synthesis. For example, Arabidopsis lines in which cytokinin action is increased have increased protein synthesis but are growth-retarded and have decreased osmotic stress tolerance. Both the osmotic stress hypersensitivity and plant growth retardation of these cytokinin gain-of-function lines can be reversed to the wild- type level by lowering their protein synthesis levels. These cytokinin gain-of-function lines, on the other hand, are more tolerant to heat and oxidative stress, indicating that optimal cytokinin action represents a balancing act in maintaining tolerance levels to a range of abiotic stresses.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.445

Funding Information

This research was supported by National Institute of Food and Agriculture HATCH project (1009329) (2016-2020), by the National Science Foundation (IOS-0919991) (2009-2014) and by the Kentucky Tobacco Research and Development Center (2016-2021).

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