Exogenous and endogenous factors controlling plastidial transcription

Plant development is highly influenced by environmental factors. Plastid gene expression was shown to differentially respond to environmental cues (Chory et al. 1995; Link 1996; Goldschmidt-Clermont 1998; Barkan and Goldschmidt-Clermont 2000). Therefore, cis- and trans-elements regulating differential gene expression in plastids were in the center of attention in the last decades (see Table 3 for summary). Regulatory sequence motifs upstream the -35 core promoter region were found in the promoters of rbcL and psbD-psbC. The rbcL gene is transcribed from a single PEP promoter with well conserved -35 and -10-elements and canonical spacing by 18 nucleotides (Shinozaki and Sugiura 1982; Mullet et al. 1985; Reinbothe et al. 1993; Isono et al. 1997a). In vitro studies demonstrated the importance of both the -35/-10 box spacing and sequence for rbcL promoter strength (Gruissem and Zurawski 1985; Hanley-Bowdoin et al. 1985). An upstream element, conserved between maize, pea, spinach, and tobacco was proposed to function as a binding site for the chloroplast DNA-binding factor 1 (CDF1) in maize (Lam et al. 1988). Interestingly, a segment of CDF1, region II, is reminiscent of the AT-rich UP element stimulating transcription in E. coli (Ross et al. 1993). However, analyses of transplastomic plants expressing chimeric PrbcL::uidA constructs demonstrated, that the rbcL core promoter is sufficient to obtain wild type rates of transcription (Shiina et al. 1998). Interestingly, another DNA-binding protein (RLBP, rbcL promoter-binding protein) binds specifically to the rbcL promoter core in tobacco (Fig. 4; -3 to -32; Kim et al. 2002). Only detectable in light-grown seedlings, RLBP is suggested to play a role in light-dependent rbcL transcription. However, stabilization of the rbcL mRNA via its 5' UTR is compensating for reduced rates of transcription in the dark and leads to light-dependent transcript accumulation (Shiina et al. 1998).

Tub Ii' 3. Transcription regulating factors in higher plants.







PEP-regulating factors

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