Abstract
Plastids contain a eubacterial-type RNA polymerase (PEP) that is responsible for transcription of photosynthesis genes encoded by plastid genome. Analogous to the eubacterial enzyme, PEP is a multi-subunit enzyme composed of a catalytic core complex (a2bbb) and a sigma factor that confers transcription specificity. Arabidopsis contains six plastid sigma factors (AtSig1-AtSig6) encoded by nuclear genome, although the core subunits are encode by plastid genome. Recently, general (AtSig6) and specialized (AtSig2 and AtSig5) sigma factors in plastids have been characterized by analyses of T-DNA tag mutants. To learn more on the functions of AtSig2 and AtSig6, we have invented double mutant plants (sig2sig6). The double mutant exhibited albino cotyledons and true leaves, although the single mutants showed pale green phenotypes. Interestingly, transcripts of psbB operon were seriously defected in the double mutant. These results suggested that AtSig2 and AtSig6 might play a major role in chloroplast transcription
