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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Claims 8
Claim · model-written summary
Putative cytochrome b561/ferric reductase and a reticulon-like protein localized to sieve-element ER.
- Organ / stage
- sieve elementse0
- Gene
- putative cytochrome b561/ferric reductase and a reticulon-like proteine0
- Outcome
- localized to the ER of sieve elementse0
Not reportedTaxon
Verbatim
e0“We identified two proteins localized to the ER of sieve elements: putative cytochrome b561/ferric reductase and a reticulon-like protein”
Claim · model-written summary
The identified ER proteins occupied segments inaccessible to HDEL-GFP.
Not reportedTaxon
Verbatim
e0“These proteins were defined to ER segments that were inaccessible to the luminal ER marker, HDEL-GFP”
Claim · model-written summary
PHLO-1 and PHLO-2 localized to sieve-element plastids and had no known conserved domains.
Not reportedTaxon
Verbatim
e0“we found proteins localized to SE-plastid. These proteins, PHLO-1 and PHLO-2, have no known conserved domains”
Claim · model-written summary
PHLO knockout plants had delayed germination.
- Taxon
- plantsViridiplantaee0
- Treatment
- knockoute0
- Outcome
- germinatione0
- Direction
- delaye0
Not reportedComparator
Verbatim
e0“the knockout plants have a delay in germination”
Claim · model-written summary
PHLO knockout plants were more sensitive to salt stress.
- Taxon
- plantsViridiplantaee0
- Treatment
- knockoute0
- Outcome
- sensitive to salt stresse0
- Direction
- more sensitivee0
Not reportedComparator
Verbatim
e0“the knockout plants have a delay in germination and are more sensitive to salt stress”
Claim · model-written summary
PHLO overexpression increased plant height.
Not reportedComparator
Verbatim
e0“Plants that overexpress PHLO have increased height and seed weight”
Claim · model-written summary
PHLO overexpression increased seed weight.
- Taxon
- PlantsViridiplantaee0
- Treatment
- overexpress PHLOe0
- Gene
- PHLOe0
- Outcome
- seed weighte0
- Direction
- increasede0
Not reportedComparator
Verbatim
e0“Plants that overexpress PHLO have increased height and seed weight”
Claim · model-written summary
Long-term aphid feeding upregulated 45 candidate proteins in sieve elements.
- Treatment
- long-term (5-week) aphid infectione0
- Interactor
- aphide0pest
- Outcome
- candidate proteinse0
- Direction
- upregulatede0
- Value
- 45 candidate proteinse0
Not reportedTaxonComparator
Verbatim
e0“Our analysis identified 45 candidate proteins that are significantly upregulated during a long-term (5-week) aphid infection”