Maize defective kernel5 is a bacterial TamB homologue required for chloroplast envelope biogenesis

Author:

Zhang Junya1ORCID,Wu Shan2,Boehlein Susan K.12,McCarty Donald R.12,Song Gaoyuan3,Walley Justin W.3ORCID,Myers Alan4ORCID,Settles A. Mark12ORCID

Affiliation:

1. Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL

2. Horticultural Sciences Department, University of Florida, Gainesville, FL

3. Plant Pathology and Microbiology, Iowa State University, Ames, IA

4. Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA

Abstract

Chloroplasts are of prokaryotic origin with a double-membrane envelope separating plastid metabolism from the cytosol. Envelope membrane proteins integrate chloroplasts with the cell, but envelope biogenesis mechanisms remain elusive. We show that maize defective kernel5 (dek5) is critical for envelope biogenesis. Amyloplasts and chloroplasts are larger and reduced in number in dek5 with multiple ultrastructural defects. The DEK5 protein is homologous to rice SSG4, Arabidopsis thaliana EMB2410/TIC236, and Escherichia coli tamB. TamB functions in bacterial outer membrane biogenesis. DEK5 is localized to the envelope with a topology analogous to TamB. Increased levels of soluble sugars in dek5 developing endosperm and elevated osmotic pressure in mutant leaf cells suggest defective intracellular solute transport. Proteomics and antibody-based analyses show dek5 reduces levels of Toc75 and chloroplast envelope transporters. Moreover, dek5 chloroplasts reduce inorganic phosphate uptake with at least an 80% reduction relative to normal chloroplasts. These data suggest that DEK5 functions in plastid envelope biogenesis to enable transport of metabolites and proteins.

Funder

National Institute of Food and Agriculture

China Scholarship Council

Vasil-Monsanto Endowment

Publisher

Rockefeller University Press

Subject

Cell Biology

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