Poster: Late and Moved Abstracts

Abs # 1379: Knock-out of the plastid sigma factor SIG6 in Arabidopsis: effects on transcription of plastid-encoded genes.

Presenter:	Ishizaki, Yoko
Authors	Ishizaki, Yoko  (A)   Tsunoyama, Yuichi  (B)   Nakahira, Yoichi  (A)   Hatano, Kyoko  (C)   Kobori, Maki  (A)   Takeba, Go  (A)   Shiina, Takashi  (A)
Affiliations:	(A): Faculty of Human Environment, Kyoto Prefectural University (B): Radio Isotope Center, Kyoto University (C): Graduate School of Human and Environmental Studies, Kyoto University

Transcription in higher plant plastids is directed by two different RNA polymerases, termed PEP (plastid-encoded bacteria-like RNA polymerase) and NEP (nuclear-encoded phage-like RNA polymerase). PEP requires a nuclear-encoded sigma factor for recognition of promoter elements. A family of six sigma factor genes has been identified in Arabidopsis. It is expected that each sigma factor may have a specific function during chloroplast development and/or under specific environmental conditions. We identified a T-DNA-generated mutation in SIG6 gene of Arabidopsis that produces chlorophyll-deficient cotyledons in young seedlings. The T-DNA insertion cosegregated with the white cotyledon phenotype. The chlorophyll-deficient phenotype was restored in 8-d old seedlings, suggesting that SIG6 has a specific function in the early stage of chloroplast development in cotyledons. The mutation caused retardation of the accumulation of plastid genes transcribed by PEP, including psbA, psbD, rbcL, rrn16, psaA, atpB and trnE. On the other hand, the SIG6 mutants accumulated high levels of mRNAs for rpoB, rpoA and clpP, which are known to have promoters recognized by NEP. Interestingly, this transcription pattern is similar to the pattern of mutant plants lacking the PEP genes. It is likely that SIG6 is a specific sigma factor involved in the recognition of usual PEP promoters in early chloroplast biogenesis.