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Dissertation
FUNCTIONAL STUDIES ON SIEVE ELEMENT-SPECIFIC PROTEINS
Washington State University
Doctor of Philosophy (PhD), Washington State University
05/2025
DOI:
https://doi.org/10.7273/000007494
Abstract
Phloem is the tissue that transports photoassimilates and macromolecules from source tissues to sink tissue. The cell responsible for all the transport is the sieve element; in its mature state, it lacks most of its major organelles, such as the nucleus; this clears the path for unobstructed flow of photoassimilates at low resistance. Despite its crucial role in the plant, very little is known about the function of organelles within sieve elements. Mitochondria, structural phloem proteins (P-proteins), endoplasmic reticulum (ER), and sieve element plastids (SE-plastids) are the only remaining components that remain. The research presented in this dissertation investigates new proteins and functional components in sieve elements. The endoplasmic reticulum (ER) in mature sieve elements lacks ribosomes and cannot synthesize proteins. Therefore, it has been suggested that proteins are imported into the sieve elements from the companion cells via the ER. We identified two proteins localized to the ER of sieve elements: putative cytochrome b561/ferric reductase and a reticulon-like protein. These proteins were defined to ER segments that were inaccessible to the luminal ER marker, HDEL-GFP, suggesting a previously unknown differentiation of the endomembrane system in sieve elements based on size (Chapter Two). In the same analysis that identified the ER-specific proteins, we found proteins localized to SE-plastid. These proteins, PHLO-1 and PHLO-2, have no known conserved domains, and our functional studies showed that the knockout plants have a delay in germination and are more sensitive to salt stress. Plants that overexpress PHLO have increased height and seed weight, suggesting a potential function of SE-plastids in phloem signaling that could be linked to abscisic acid (ABA) metabolism (Chapter Four). In addition, we used our methodology of isolating sieve elements to study how the proteome of sieve elements changes during aphid feeding. Our analysis identified 45 candidate proteins that are significantly upregulated during a long-term (5-week) aphid infection (Chapter Three).
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Details
- Title
- FUNCTIONAL STUDIES ON SIEVE ELEMENT-SPECIFIC PROTEINS
- Creators
- Viktoriya V. Vasina
- Contributors
- Michael Knoblauch (Chair)Asaph Cousins (Committee Member)Thomas Okita (Committee Member)Hanjo Hellmann (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Biological Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 141
- Identifiers
- 99901221149601842
- Language
- English
- Resource Type
- Dissertation