Functional characterization of a novel transport protein regulating cytokinin activity in plants
Final Report Abstract
The phytohormone cytokinin is an important regulator of plant growth and development. Its key function is to control formation and maintenance of meristems that are essential to establish the whole plant body. Cytokinin sustains the shoot apical meristem activity and its degradation by cytokinin oxidases/dehydrogenases (CKXs) is crucial to define the hormone status in the meristem. In this project, we have identified ROCK1 protein as a specific type of nucleotide sugar transporter localized to the endoplasmic reticulum (ER). It has been shown that mutant alleles of ROCK1 suppress phenotypes inferred by a reduced cytokinin concentration by diminishing CKX protein levels, indicating that ROCK1 functions in maintaining the CKX activity to lower cytokinin responses. The results also showed that CKX isoforms expressed specifically in shoot apical meristem are direct targets of ROCK1. Further experiments revealed that the ER-localized CKX proteins are degraded by the cytosolic proteasome machinery in a process called ER-associated degradation (ERAD) and that ROCK1 is a functional component of this cellular pathway. The project has contributed to the understanding of the role of ERAD in regulating cytokinin homeostasis and plant growth.
Publications
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(2015). Arabidopsis ROCK1 transports UDP-GlcNAc/UDP-GalNAc and regulates ER protein quality control and cytokinin activity. Proc. Natl. Acad. Sci. USA 112: 291-296
Niemann M.C.E., Bartrina I., Ashikov A., Weber H., Novák O., Spíchal L., Strnad M., Strasser R., Bakker H., Schmülling T., Werner T.
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(2018) The cytokinin oxidase/dehydrogenase CKX1 is a membrane-bound protein requiring homooligomerization in the endoplasmic reticulum for its cellular activity. Plant Physiol. 176: 2024-2039
Niemann M.C.E., Weber H., Hluska T., Leonte G., Anderson S.M., Senes A., Werner T.
