Genetics, Vol 145, 467-478, Copyright © 1997

INVESTIGATIONS

Transposon-Disruption of a Maize Nuclear Gene, tha1, Encoding a Chloroplast SecA Homologue: In Vivo Role of cp-SecA in Thylakoid Protein Targeting

R. Voelker, J. Mendel-Hartvig and A. Barkan
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403

A nuclear mutant of maize, tha1, which exhibited defects in the translocation of proteins across the thylakoid membrane, was described previously. A transposon insertion at the tha1 locus facilitated the cloning of portions of the tha1 gene. Strong sequence similarity with secA genes from bacteria, pea and spinach indicates that tha1 encodes a SecA homologue (cp-SecA). The tha1-ref allele is either null or nearly so, in that tha1 mRNA is undetectable in mutant leaves and cp-SecA accumulation is reduced >=40-fold. These results, in conjunction with the mutant phenotype described previously, demonstrate that cp-SecA functions in vivo to facilitate the translocation of OEC33, PSI-F and plastocyanin but does not function in the translocation of OEC23 and OEC16. Our results confirm predictions for cp-SecA function made from the results of in vitro experiments and establish several new functions for cp-SecA, including roles in the targeting of a chloroplast-encoded protein, cytochrome f, and in protein targeting in the etioplast, a nonphotosynthetic plastid type. Our finding that the accumulation of properly targeted plastocyanin and cytochrome f in tha1-ref thylakoid membranes is reduced only a few-fold despite the near or complete absence of cp-SecA suggests that cp-SecA facilitates but is not essential in vivo for their translocation across the membrane.

This article has been cited by other articles:

				S. M. Gross and J. B. Hollick Multiple Trans-Sensing Interactions Affect Meiotically Heritable Epigenetic States at the Maize pl1 Locus Genetics, June 1, 2007; 176(2): 829 - 839. [Abstract] [Full Text] [PDF]

				C. Sun, S. L. Rusch, J. Kim, and D. A. Kendall Chloroplast SecA and Escherichia coli SecA Have Distinct Lipid and Signal Peptide Preferences J. Bacteriol., February 1, 2007; 189(3): 1171 - 1175. [Abstract] [Full Text] [PDF]

				J. B. Hollick, J. L. Kermicle, and S. E. Parkinson Rmr6 Maintains Meiotic Inheritance of Paramutant States in Zea mays Genetics, October 1, 2005; 171(2): 725 - 740. [Abstract] [Full Text] [PDF]

				C.-W. Sun, L.-J. Chen, L.-C. Lin, and H.-m. Li Leaf-Specific Upregulation of Chloroplast Translocon Genes by a CCT Motif-Containing Protein, CIA 2 PLANT CELL, September 1, 2001; 13(9): 2053 - 2061. [Abstract] [Full Text] [PDF]

				A. M. Settles, A. Baron, A. Barkan, and R. A. Martienssen Duplication and Suppression of Chloroplast Protein Translocation Genes in Maize Genetics, January 1, 2001; 157(1): 349 - 360. [Abstract] [Full Text]

				M. B. Walker, L. M. Roy, E. Coleman, R. Voelker, and A. Barkan The Maize tha4 Gene Functions in Sec-Independent Protein Transport in Chloroplasts and Is Related to hcf106, tatA, and tatB J. Cell Biol., October 18, 1999; 147(2): 267 - 276. [Abstract] [Full Text] [PDF]

				P. Amin, D. A.C. Sy, M. L. Pilgrim, D. H. Parry, L. Nussaume, and N. E. Hoffman Arabidopsis Mutants Lacking the 43- and 54-Kilodalton Subunits of the Chloroplast Signal Recognition Particle Have Distinct Phenotypes Plant Physiology, September 1, 1999; 121(1): 61 - 70. [Abstract] [Full Text]

				E. Houben, J.-W. de Gier, and K. J. van Wijk Insertion of Leader Peptidase into the Thylakoid Membrane during Synthesis in a Chloroplast Translation System PLANT CELL, August 1, 1999; 11(8): 1553 - 1564. [Abstract] [Full Text]

				D. Schuenemann, P. Amin, E. Hartmann, and N. E. Hoffman Chloroplast SecY Is Complexed to SecE and Involved in the Translocation of the 33-kDa but Not the 23-kDa Subunit of the Oxygen-evolving Complex J. Biol. Chem., April 23, 1999; 274(17): 12177 - 12182. [Abstract] [Full Text] [PDF]

				K. Keegstra and K. Cline Protein Import and Routing Systems of Chloroplasts PLANT CELL, April 1, 1999; 11(4): 557 - 570. [Full Text]

				L. Leloup, A. J. M. Driessen, R. Freudl, R. Chambert, and M.-F. Petit-Glatron Differential Dependence of Levansucrase and alpha -Amylase Secretion on SecA (Div) during the Exponential Phase of Growth of Bacillus subtilis J. Bacteriol., March 15, 1999; 181(6): 1820 - 1826. [Abstract] [Full Text]

				E. J. Summer and K. Cline Red Bell Pepper Chromoplasts Exhibit in Vitro Import Competency and Membrane Targeting of Passenger Proteins from the Thylakoidal Sec and Delta pH Pathways but Not the Chloroplast Signal Recognition Particle Pathway Plant Physiology, February 1, 1999; 119(2): 575 - 584. [Abstract] [Full Text]

				K. K. Bernd and B. D. Kohorn Tip Loci: Six Chlamydomonas Nuclear Suppressors That Permit the Translocation of Proteins with Mutant Thylakoid Signal Sequences Genetics, July 1, 1998; 149(3): 1293 - 1301. [Abstract] [Full Text] [PDF]

				L. M. Roy and A. Barkan A SecY Homologue Is Required for the Elaboration of the Chloroplast Thylakoid Membrane and for Normal Chloroplast Gene Expression J. Cell Biol., April 20, 1998; 141(2): 385 - 395. [Abstract] [Full Text] [PDF]

				E. A. Leheny, S. A. Teter, and S. M. Theg Identification of a Role for an Azide-Sensitive Factor in the Thylakoid Transport of the 17-Kilodalton Subunit of the Photosynthetic Oxygen-Evolving Complex Plant Physiology, February 1, 1998; 116(2): 805 - 814. [Abstract] [Full Text] [PDF]

				T. Rohl and K. J. van Wijk In Vitro Reconstitution of Insertion and Processing of Cytochrome f in a Homologous Chloroplast Translation System J. Biol. Chem., September 14, 2001; 276(38): 35465 - 35472. [Abstract] [Full Text] [PDF]

				L. Zhang, V. Paakkarinen, M. Suorsa, and E.-M. Aro A SecY Homologue Is Involved in Chloroplast-encoded D1 Protein Biogenesis J. Biol. Chem., October 5, 2001; 276(41): 37809 - 37814. [Abstract] [Full Text] [PDF]