Dissertation
THE PLASTIDIAL ΑLPHA-GLUCAN PHOSPHORYLASE HAS AN UNEXPECTED ROLE IN PHOTOSYNTHESIS
Doctor of Philosophy (PhD), Washington State University
01/2019
Handle:
https://hdl.handle.net/2376/110961
Abstract
In plants, there are two isoforms of phosphorylase with different subcellular localization; cytosolic Pho2 and plastidial Pho1. Pho2, structurally and functionally resemble glycogen phosphorylases, and is involved in the degradation of maltose. Pho1 also resembles glycogen phosphorylases structurally, apart from a 50-80 amino acid long domain (L80) with unknown function. Recent genetic studies identified Pho1 as a component of starch biosynthesis in rice and Chlamydomonas reinhardtii. Even then, the role of the L80 region remained puzzling as its removal (Pho1ΔL80) did not alter the kinetic properties of recombinant rice Pho1ΔL80. In this dissertation, I present my findings on the role of Pho1 and its L80 region in rice (Oryza sativa). To study the role of Pho1 and characterize the role of the L80 region, I complemented pho1- mutant rice plant (BMF136) either with the wildtype Pho1 or the Pho1 gene lacking L80 region (Pho1ΔL80). Complementation of BMF136 by Pho1 restored normal seed phenotype and growth. By contrast, complementation of BMF136 by Pho1ΔL80 enhanced seed weight, plant productivity and growth rate above wildtype levels. Analysis of proteins interacting with Pho1 identified PsaC subunit of photosystem-I. To identify the physiological role of Pho1-PsaC interaction in photosynthesis, we investigated the PSI and gas exchange properties of wildtype, BMF136 and transgenic BMF136 plants. The result of these experiments revealed that while the removal of Pho1 reduced photosynthetic efficiency below wildtype in vivo, the removal of just the L80 region of Pho1 increases photosynthetic efficiency above wildtype in vivo. Although the expression of Pho1ΔL80 and not Pho1 stimulated PSI in vivo, both Pho1 and Pho1ΔL80 stimulated PSI equally in vitro. These differences suggest the presence of an in vivo regulatory process that acts through the L80 region, and regulates the Pho1 stimulation of PSI. Pho1ΔL80 expressing BMF136 plants were severely stressed under cold, revealing that the L80 region is an essential regulator of Pho1 stimulation of PSI under cold stress. Overall, these findings provide novel insight into the role of rice Pho1 and its L80 region, and how it can play a role in the photosynthesis.
Metrics
65 File views/ downloads
28 Record Views
Details
- Title
- THE PLASTIDIAL ΑLPHA-GLUCAN PHOSPHORYLASE HAS AN UNEXPECTED ROLE IN PHOTOSYNTHESIS
- Creators
- Kaan Koper
- Contributors
- Thomas W Okita (Advisor)Chulhee Kang (Committee Member)Asaph Cousins (Committee Member)Hanjo Hellmann (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Program in Molecular Plant Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 127
- Identifiers
- 99900581501601842
- Language
- English
- Resource Type
- Dissertation