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JXB Advance Access published online on June 1, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm100
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Characterization of monofunctional aspartate kinase genes in maize and their relationship with free amino acid content in the endosperm

Xuelu Wang1 *, Jose A. Lopez-Valenzuela1 {dagger}, Bryan C. Gibbon1, Bertrand Gakiere2 {ddagger}, Gad Galili2 and Brian A. Larkins1,§

1Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA
2Department of Plant Science, Weizmann Institute, 76100 Rehovot, Israel

§ To whom correspondence should be addressed. E-mail: Larkins{at}Ag.Arizona.edu

A quantitative trait locus has previously been identified in maize (Zea mays L.) that influences the level of free amino acids in the endosperm, especially those from the aspartate pathway: lysine, threonine, methionine, leucine, and isoleucine. Because this locus occurs in a region of the genome containing ask2, a monofunctional aspartate kinase, the nature of the monofunctional aspartate kinase genes in the parental inbreds, Oh545o2 and Oh51Ao2, was investigated. Two genes, Ask1 and Ask2 were isolated, and Ask2 was mapped to the ask2 locus. Nucleotide sequence analysis of the Ask2 alleles from Oh545o2 and Oh51Ao2 showed they differ by one amino acid. Both alleles complemented a yeast aspartate kinase mutant, hom3, and based on the growth of the yeast mutant it appeared that Ask2-Oh545o2 produces an enzyme with greater total activity than that encoded by the Oh51Ao2 allele. The results suggest that the higher level of free amino acids derived from the aspartate pathway in Oh545o2 endosperm results from a single amino acid change in the ASK2 enzyme that has pleiotropic effects on its activity.

Key words: Aspartate kinase, endosperm, lysine, opaque2, Zea mays

* Present address: The State Key Laboratory of Genetic Engineering, The School of Life Sciences, Fudan University, Shanghai 200433, China.

{dagger} Present address: Facultad de Ciencias Químico-Biológicas, Universidad Autónoma de Sinaloa, 80000 Culiacán Sin, Mexico.

{ddagger} Present address: Université Paris-Sud, Institut de Biotechnologie des Plantes, UMR 8618, F-91405, Orsay, France.

Received 2 March 2007; Revised 6 April 2007 Accepted 17 April 2007


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