Skip to main content
PMC home page
Genetics logoLink to Genetics
. 1997 Feb;145(2):467–478. doi: 10.1093/genetics/145.2.467

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 1, J Mendel-Hartvig 1, A Barkan 1
PMCID: PMC1207810  PMID: 9071599

Abstract

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.

Full Text

The Full Text of this article is available as a PDF (6.2 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Barkan A. Nuclear Mutants of Maize with Defects in Chloroplast Polysome Assembly Have Altered Chloroplast RNA Metabolism. Plant Cell. 1993 Apr;5(4):389–402. doi: 10.1105/tpc.5.4.389. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Barkan A., Walker M., Nolasco M., Johnson D. A nuclear mutation in maize blocks the processing and translation of several chloroplast mRNAs and provides evidence for the differential translation of alternative mRNA forms. EMBO J. 1994 Jul 1;13(13):3170–3181. doi: 10.1002/j.1460-2075.1994.tb06616.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Chandler V. L., Hardeman K. J. The Mu elements of Zea mays. Adv Genet. 1992;30:77–122. doi: 10.1016/s0065-2660(08)60319-3. [DOI] [PubMed] [Google Scholar]
  4. Cline K., Henry R. Import and routing of nucleus-encoded chloroplast proteins. Annu Rev Cell Dev Biol. 1996;12:1–26. doi: 10.1146/annurev.cellbio.12.1.1. [DOI] [PubMed] [Google Scholar]
  5. Flachmann R., Michalowski C. B., Löffelhardt W., Bohnert H. J. SecY, an integral subunit of the bacterial preprotein translocase, is encoded by a plastid genome. J Biol Chem. 1993 Apr 5;268(10):7514–7519. [PubMed] [Google Scholar]
  6. Franklin A. E., Hoffman N. E. Characterization of a chloroplast homologue of the 54-kDa subunit of the signal recognition particle. J Biol Chem. 1993 Oct 15;268(29):22175–22180. [PubMed] [Google Scholar]
  7. Glick B. S., Beasley E. M., Schatz G. Protein sorting in mitochondria. Trends Biochem Sci. 1992 Nov;17(11):453–459. doi: 10.1016/0968-0004(92)90487-t. [DOI] [PubMed] [Google Scholar]
  8. Hartl F. U., Ostermann J., Guiard B., Neupert W. Successive translocation into and out of the mitochondrial matrix: targeting of proteins to the intermembrane space by a bipartite signal peptide. Cell. 1987 Dec 24;51(6):1027–1037. doi: 10.1016/0092-8674(87)90589-7. [DOI] [PubMed] [Google Scholar]
  9. Henry R., Kapazoglou A., McCaffery M., Cline K. Differences between lumen targeting domains of chloroplast transit peptides determine pathway specificity for thylakoid transport. J Biol Chem. 1994 Apr 8;269(14):10189–10192. [PubMed] [Google Scholar]
  10. Karnauchov I., Cai D., Schmidt I., Herrmann R. G., Klösgen R. B. The thylakoid translocation of subunit 3 of photosystem I, the psaF gene product, depends on a bipartite transit peptide and proceeds along an azide-sensitive pathway. J Biol Chem. 1994 Dec 30;269(52):32871–32878. [PubMed] [Google Scholar]
  11. Knott T. G., Robinson C. The secA inhibitor, azide, reversibly blocks the translocation of a subset of proteins across the chloroplast thylakoid membrane. J Biol Chem. 1994 Mar 18;269(11):7843–7846. [PubMed] [Google Scholar]
  12. Laidler V., Chaddock A. M., Knott T. G., Walker D., Robinson C. A SecY homolog in Arabidopsis thaliana. Sequence of a full-length cDNA clone and import of the precursor protein into chloroplasts. J Biol Chem. 1995 Jul 28;270(30):17664–17667. doi: 10.1074/jbc.270.30.17664. [DOI] [PubMed] [Google Scholar]
  13. Li X., Henry R., Yuan J., Cline K., Hoffman N. E. A chloroplast homologue of the signal recognition particle subunit SRP54 is involved in the posttranslational integration of a protein into thylakoid membranes. Proc Natl Acad Sci U S A. 1995 Apr 25;92(9):3789–3793. doi: 10.1073/pnas.92.9.3789. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Luehrsen K. R., Taha S., Walbot V. Nuclear pre-mRNA processing in higher plants. Prog Nucleic Acid Res Mol Biol. 1994;47:149–193. doi: 10.1016/s0079-6603(08)60252-4. [DOI] [PubMed] [Google Scholar]
  15. Mant A., Nielsen V. S., Knott T. G., Møller B. L., Robinson C. Multiple mechanisms for the targeting of photosystem I subunits F, H, K, L, and N into and across the thylakoid membrane. J Biol Chem. 1994 Nov 4;269(44):27303–27309. [PubMed] [Google Scholar]
  16. Martienssen R. A., Barkan A., Freeling M., Taylor W. C. Molecular cloning of a maize gene involved in photosynthetic membrane organization that is regulated by Robertson's Mutator. EMBO J. 1989 Jun;8(6):1633–1639. doi: 10.1002/j.1460-2075.1989.tb03553.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Nakai M., Goto A., Nohara T., Sugita D., Endo T. Identification of the SecA protein homolog in pea chloroplasts and its possible involvement in thylakoidal protein transport. J Biol Chem. 1994 Dec 16;269(50):31338–31341. [PubMed] [Google Scholar]
  18. Nelson T., Harpster M. H., Mayfield S. P., Taylor W. C. Light-regulated gene expression during maize leaf development. J Cell Biol. 1984 Feb;98(2):558–564. doi: 10.1083/jcb.98.2.558. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Nohara T., Nakai M., Goto A., Endo T. Isolation and characterization of the cDNA for pea chloroplast SecA. Evolutionary conservation of the bacterial-type SecA-dependent protein transport within chloroplasts. FEBS Lett. 1995 May 15;364(3):305–308. doi: 10.1016/0014-5793(95)00415-6. [DOI] [PubMed] [Google Scholar]
  20. Reith M., Munholland J. A High-Resolution Gene Map of the Chloroplast Genome of the Red Alga Porphyra purpurea. Plant Cell. 1993 Apr;5(4):465–475. doi: 10.1105/tpc.5.4.465. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Robinson C., Klösgen R. B. Targeting of proteins into and across the thylakoid membrane--a multitude of mechanisms. Plant Mol Biol. 1994 Oct;26(1):15–24. doi: 10.1007/BF00039516. [DOI] [PubMed] [Google Scholar]
  22. Scaramuzzi C. D., Hiller R. G., Stokes H. W. Identification of a chloroplast-encoded secA gene homologue in a chromophytic alga: possible role in chloroplast protein translocation. Curr Genet. 1992 Nov;22(5):421–427. doi: 10.1007/BF00352444. [DOI] [PubMed] [Google Scholar]
  23. Smeekens S., Weisbeek P., Robinson C. Protein transport into and within chloroplasts. Trends Biochem Sci. 1990 Feb;15(2):73–76. doi: 10.1016/0968-0004(90)90180-j. [DOI] [PubMed] [Google Scholar]
  24. Voelker R., Barkan A. Two nuclear mutations disrupt distinct pathways for targeting proteins to the chloroplast thylakoid. EMBO J. 1995 Aug 15;14(16):3905–3914. doi: 10.1002/j.1460-2075.1995.tb00062.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Yuan J., Henry R., McCaffery M., Cline K. SecA homolog in protein transport within chloroplasts: evidence for endosymbiont-derived sorting. Science. 1994 Nov 4;266(5186):796–798. doi: 10.1126/science.7973633. [DOI] [PubMed] [Google Scholar]
  26. de Boer D., Cremers F., Teertstra R., Smits L., Hille J., Smeekens S., Weisbeek P. In vivo import of plastocyanin and a fusion protein into developmentally different plastids of transgenic plants. EMBO J. 1988 Sep;7(9):2631–2635. doi: 10.1002/j.1460-2075.1988.tb03115.x. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Genetics are provided here courtesy of Oxford University Press

RESOURCES