Analysis of promoter selectivity of plastid sigma factors in Arabidopsis thaliana

Abstract

In higher plants, chloroplasts have at least two types of RNA polymerases(RNAPs), the bacterial-type RNAP (PEP; plastid-encoded RNAP) and the T7 bacteriophage type RNAP (NEP; nuclear-encoded RNAP). PEP transcribes preferentially the genes encoding the proteins implicated in the characteristic functions of chloroplasts and is composed of plastid-encoded core enzyme subunits and a nuclear-encoded sigma factor, which presumably confer promoter-specific transcription initiation on RNAP. In higher plant genome analysis, a number of putative sigma factors have been identified. These multiple sigma factors are considered to recognize different sets of promoter sequences and regulate the activity of PEP in response to the developmental stage and various environmental clues. To analyze the promoter selectivity of sigma factors in Arabidopsis thaliana, each of six sig genes was expressed transiently in protoplasts and the transcription of 12 plastid genes in each transformant was measured by means of the run-on transcription assay. In this assay, three sigma factors were found to elevate the PEP activity for different plastid genes, indicating that each sigma factor has different promoter recognition property. The regulation mechanism of transcription of plastid genes through sigma factors will be discussed.