Campus Units

Agronomy, Biochemistry, Biophysics and Molecular Biology, Roy J. Carver Department of

Document Type

Article

Publication Version

Published Version

Publication Date

1-2-2018

Journal or Book Title

Proceedings of the National Academy of Sciences of the United States of America

Volume

115

Issue

1

First Page

E24

Last Page

E33

DOI

10.1073/pnas.1715668115

Abstract

Maize opaque2 (o2) mutations are beneficial for endosperm nutritional quality but cause negative pleiotropic effects for reasons that are not fully understood. Direct targets of the bZIP transcriptional regulator encoded by o2 include pdk1 and pdk2 that specify pyruvate phosphate dikinase (PPDK). This enzyme reversibly converts AMP, pyrophosphate, and phosphoenolpyruvate to ATP, orthophosphate, and pyruvate and provides diverse functions in plants. This study addressed PPDK function in maize starchy endosperm where it is highly abundant during grain fill. pdk1 and pdk2 were inactivated individually by transposon insertions, and both genes were simultaneously targeted by endosperm-specific RNAi. pdk2 accounts for the large majority of endosperm PPDK, whereas pdk1 specifies the abundant mesophyll form. The pdk1- mutation is seedling-lethal, indicating that C4 photosynthesis is essential in maize. RNAi expression in transgenic endosperm eliminated detectable PPDK protein and enzyme activity. Transgenic kernels weighed the same on average as nontransgenic siblings, with normal endosperm starch and total N contents, indicating that PPDK is not required for net storage compound synthesis. An opaque phenotype resulted from complete PPDK knockout, including loss of vitreous endosperm character similar to the phenotype conditioned by o2-. Concentrations of multiple glycolytic intermediates were elevated in transgenic endosperm, energy charge was altered, and starch granules were more numerous but smaller on average than normal. The data indicate that PPDK modulates endosperm metabolism, potentially through reversible adjustments to energy charge, and reveal that o2- mutations can affect the opaque phenotype through regulation of PPDK in addition to their previously demonstrated effects on storage protein gene expression.

Comments

This article is published as Ryan R. Lappe, John W. Baier, Susan K. Boehlein, Ryan Huffman, Qiaohui Lin, Fabrice Wattebled, A. Mark Settles, L. Curtis Hannah, Ljudmilla Borisjuk, Hardy Rolletschek, Jon D. Stewart, M. Paul Scott, Tracie A. Hennen-Bierwagen, and Alan M. Myers. Functions of maize genes encoding pyruvate phosphate dikinase in developing endosperm. PNAS 2018 115 (1) E24-E33. doi: 10.1073/pnas.1715668115.

Rights

Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.

Language

en

File Format

application/pdf

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