The plastid genome of higher plants contains more than one hundred genes for photosynthesis,
gene expression, and other processes. Plastid transcription is done by two types of
RNA polymerase, PEP and NEP. PEP is a eubacteria-type RNA polymerase that is essential
for chloroplast development. In Arabidopsis thaliana, six sigma factors (SIG1-6) are
encoded by the nuclear genome, and postulated to determine the transcription specificity
of PEP. In this study, we constructed a DNA microarray for all of the plastid protein-coding
genes, and analyzed the effects of the sig2 lesion on the global plastid gene expression.
Of the 79 plastid protein genes, it was found that only the psaJ transcript was decreased
in the mutant, whereas transcripts of 47 genes were rather increased. Since many of
the upregulated genes are under the control of NEP, it was suggested that the NEP
activity was increased in the sig2-1 mutant.