The Etched1 gene of Zea mays (L.) encodes a zinc ribbon protein that belongs to the transcriptionally active chromosome (TAC) of plastids and is similar to the transcription factor TFIIS

doi:10.1111/j.1365-313X.2004.02094.x

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Wiley InterScience

The Plant Journal

Volume 38 Issue 6, Pages 923 - 939

Published Online: 29 Apr 2004

Published in association with the Society for Experimental Biology

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The Etched1 gene of Zea mays (L.) encodes a zinc ribbon protein that belongs to the transcriptionally active chromosome (TAC) of plastids and is similar to the transcription factor TFIIS

Oswaldo da Costa e Silva ^1,†,‡ , René Lorbiecke ^1,‡ , Preeti Garg ¹ , Lenard Müller ² , Martina Waßmann ¹ , Patricia Lauert ¹ , Mike Scanlon ³ , An-Ping Hsia ⁴ , Patrick S. Schnable ⁴ , Karin Krupinska ² and Udo Wienand ^1,*

¹ Institut für Allgemeine Botanik und Botanischer Garten, Universität Hamburg, Ohnhorststr. 18, D-22 609 Hamburg, Germany, ² Botanisches Institut der Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany, ³ University Georgia, 3609 Plant Sciences, Athens, GA 30602, USA, and ⁴ Department of Agronomy and Center for Plant Genomics, Iowa State University, Ames, IA 50011, USA

^* For correspondence (fax +49 40 42816503; e-mail udo.wien@uni-hamburg.de).

^† Present address: BASF Plant Science GmbH, BPS-A30, 67056 Ludwigshafen, Germany.

^‡ Both authors contributed equally to this paper.

KEYWORDS

etched1 • plastid nucleoids • transcriptional active chromosome • transposon tagging • plastid transcription • TFIIS

ABSTRACT

Etched1 (et1) is a pleiotropic, recessive mutation of maize that causes fissured and cracked mature kernels and virescent seedlings. Microscopic examinations of the et1 phenotype revealed an aberrant plastid development in mutant kernels and mutant leaves. Here, we report on the cloning of the et1 gene by transposon tagging, the localization of the gene product in chloroplasts, and its putative function in the plastid transcriptional apparatus. Several alleles of Mutator (Mu)-induced et1 mutants, the et1-reference (et1-R) mutant, and Et1 wild-type were cloned and analyzed at the molecular level. Northern analyses with wild-type plants revealed that Et1 transcripts are present in kernels, leaves, and other types of tissue, and no Et1 expression could be detected in the et1 mutants analyzed. The ET1 protein is imported by chloroplasts and has been immunologically detected in transcriptionally active chromosome (TAC) fractions derived from chloroplasts. Accordingly, the relative transcriptional activity of TAC fractions was significantly reduced in chloroplasts of et1-R plants. ET1 is the first zinc ribbon (ZR) protein shown to be targeted to plastids. With regard to its localization and its striking structural similarity to the eukaryotic transcription elongation factor TFIIS, it is feasible that ET1 functions in plastid transcription elongation by reactivation of arrested RNA polymerases.