Introduction

Already at the beginning of the last century, the German geneticist and plant breeder Erwin Baur proposed that the non-Mendelian inheritance of leaf variegations can be explained with the assumption that chloroplasts (plastids) contain their own genetic material (Baur 1909, 1910; reviewed in Hagemann 2000, 2002). More than half a century later, the discovery of plastid DNA (Chun et al. 1963; Sager and Ishida 1963; Tewari and Wildman 1966) ultimately confirmed Baur's ingenious hypothesis. During the following decades, the plastid genome (plas-tome), its coding capacity and gene expression have been the subject of extensive molecular studies and today, the chloroplast represents the by far best-studied genetic compartment of the plant cell.

Due to its cyanobacterial ancestry, the plastome has retained numerous pro-karyotic features, including a bacterial-type circular genome structure, genome packaging in nucleoids, organization of genes in operons, and a prokaryotic gene

Topics in Current Genetics, Vol. 19

R. Bock (Ed.): Cell and Molecular Biology of Plastids

DOI 10.1007/4735_2007_0223 / Published online: 14 April 2007

© Springer-Verlag Berlin Heidelberg 2007

Fig. 1. Physical map of the tomato (Solanum lycopersicum, formerly Lycopersicon esculen-tum) plastid genome as a typical example of a plastid genome in higher plants (modified from Kahlau et al. 2006). Genes inside the circle are transcribed clockwise; genes outside the circle are transcribed counterclockwise. The two large inverted repeat regions IRA and IRB are shown as fat lines. Asterisks indicate intron-containing genes; introns are depicted as open boxes. For gene products and their functions, compare Table 1.

Fig. 1. Physical map of the tomato (Solanum lycopersicum, formerly Lycopersicon esculen-tum) plastid genome as a typical example of a plastid genome in higher plants (modified from Kahlau et al. 2006). Genes inside the circle are transcribed clockwise; genes outside the circle are transcribed counterclockwise. The two large inverted repeat regions IRA and IRB are shown as fat lines. Asterisks indicate intron-containing genes; introns are depicted as open boxes. For gene products and their functions, compare Table 1.

expression machinery. This chapter provides an overview of our current understanding of (i) the structural properties of the plastid DNA, (ii) structure and function of the plastome and (iii) the inheritance of plastids and their genomes.

Table 1. Plastid-encoded genes and conserved open reading frames (ycf = hypothetical chloroplast reading frame) in higher plants

Gene

Gene product

Functions and remarks

psaA

A subunit of PSI

reaction center subunit, essential for PSI function

psaB

B subunit of PSI

reaction center subunit, essential for PSI function

psaC

C subunit of PSI

essential cofactor-binding subunit

psaI

I subunit of PSI

small subunit, not essential for PSI function

psaJ

J subunit of PSI

small subunit, not essential for PSI function

ycf

Ycf3 protein

essential PSI assembly factor, contains three tetratricopeptide (TPR) repeats

ycf4

Ycf4 protein

essential PSI assembly factor

psbA

D1 protein of PSII

reaction center, also termed 'herbicide-binding protein', essential for PSII function

psbB

CP47 subunit of PSII

inner antenna protein, essential for PSII function

psbC

CP43 subunit of PSII

inner antenna protein, essential for PSII function

psbD

D2 protein of PSII

reaction center, essential for PSII function

psbE

a-subunit of cyto

essential for PSII assembly/stability/function,

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