Plastidial transporters KEA1, -2, and -3 are essential for chloroplast osmoregulation, integrity, and pH regulation in Arabidopsis
- Univ. of California, San Diego, La Jolla, CA (United States)
- Univ. of Cologne (Germany)
- Univ. of Gothenburg (Sweden)
- Michigan State Univ., East Lansing, MI (United States)
Multiple K+ transporters and channels and the corresponding mutants have been described and studied in the plasma membrane and organelle membranes of plant cells. However, knowledge about the molecular identity of chloroplast K+ transporters is limited. Potassium transport and a well-balanced K+ homeostasis were suggested to play important roles in chloroplast function. Because no loss-of-function mutants have been identified, the importance of K+ transporters for chloroplast function and photosynthesis remains to be determined. In this paper, we report single and higher-order loss-of-function mutants in members of the cation/proton antiporters-2 antiporter superfamily KEA1, KEA2, and KEA3. KEA1 and KEA2 proteins are targeted to the inner envelope membrane of chloroplasts, whereas KEA3 is targeted to the thylakoid membrane. Higher-order but not single mutants showed increasingly impaired photosynthesis along with pale green leaves and severely stunted growth. The pH component of the proton motive force across the thylakoid membrane was significantly decreased in the kea1kea2 mutants, but increased in the kea3 mutant, indicating an altered chloroplast pH homeostasis. Electron microscopy of kea1kea2 leaf cells revealed dramatically swollen chloroplasts with disrupted envelope membranes and reduced thylakoid membrane density. Unexpectedly, exogenous NaCl application reversed the observed phenotypes. Furthermore, the kea1kea2 background enables genetic analyses of the functional significance of other chloroplast transporters as exemplified here in kea1kea2Na+/H+ antiporter1 (nhd1) triple mutants. Taken together, the presented data demonstrate a fundamental role of inner envelope KEA1 and KEA2 and thylakoid KEA3 transporters in chloroplast osmoregulation, integrity, and ion and pH homeostasis.
- Research Organization:
- Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Laboratory
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF); National Institute of Environmental Health Sciences (NIEHS)
- Grant/Contract Number:
- FG02-91ER20021; FG02-03ER15449; MCB0918220; P42ES010337
- OSTI ID:
- 1602746
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Vol. 111, Issue 20; ISSN 0027-8424
- Publisher:
- National Academy of SciencesCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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