Characterization and environmental regulation of a 24 kilo-Dalton cornus sericea dehydrin-like protein and its relationship to freeze-tolerance
Abstract
We have been interested in studying the molecular mechanisms of freeze-tolerance in woody plants. To address this question, seasonal protein extractions were taken from red-osier dogwood (Corpus sericea L.) xylem in an attempt to identify proteins associated with cold acclimation in extremely freeze-tolerant organism. A 24 kDa protein was found to have maximum accumulation during periods of cold acclimation. A polyclonal antibody was raised against this protein and used for subsequent screening of a cDNA expression library generated from cold acclimated xylem. Four unique cDNA s were subsequently sequenced and found to encode putative novel dehydrin-like proteins. Immunogold in situ localization, using the anti-24 kDa antibody, revealed abundant labeling throughout the cytosol and nuclei of cold acclimated xylem ray parenchyma, pith parenchyma, and cortical tissues. In addition, a novel association with plasmodesmata was observed within the simple pits of xylem ray parenchyma and adjacent differentiating xylem cell types. Although the dehydrin function remains unknown, they may non-specifically stabilize nuclear and cytosolic macromolecules and membrane surfaces during periods of desiccation. Previous studies have related the occurrence of dehydrins during cold acclimation due to the desiccative stress induced by the formation of extracellular ice during freezing. As a result, it was of interest to determine the environmental regulatory mechanism for 24 kDa protein accumulation. Through extensive controlled photoperiod and field studies, we determined that the 24 kDa dehydrin-like protein accumulates in response to prolonged short day exposure and is phytochrome mediated. Through usage of climatic ecotypes, we have confirmed that this photoperiod regulation is under genetic control. Decreasing photoperiod in late summer triggered a series of physiological events that ultimately reduced stem water content, enhanced freeze-tolerance and increased 24 kDa protein accumulation. As a result, freeze-tolerance was acquired prior to the onset of the first frost episodes. Interspecific analyses between 24 Cornus species determined that 24 kDa protein occurrence is widespread and occurs in both supercooling and non-supercooling tissues. Due to the commonality of the 24 kDa protein in less hardy species, we are unsure of the 24 kDa protein s role in the extreme freeze tolerance that is characteristic of C. sericea .
Degree
Ph.D.
Advisors
Ashworth, Purdue University.
Subject Area
Botany
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.