SPATIAL AND TEMPORAL PATTERN OF LIGHT-REGULATED GENE-EXPRESSION DURING TOBACCO SEEDLING DEVELOPMENT - THE PHOTOSYSTEM II-RELATED GENES LHCB (CAB) AND PSBP (OEE2)

The white mustard (Sinapis alba L.) Lhcb1*1 and PsbP*1 genes that code for proteins related to photosystem II (PSII) in chloroplasts were examined by analysis of promoter fragment beta-glucuronidase (GUS) reporter constructs in transgenic tobacco (Nicotiana tabacum L.) seedlings. The endogenous tobacco genes and the introduced mustard genes follow the same kinetics during seedling development and they show the same expression characteristics for light regulation and for the influence of a 'plastidic signal'. Hence, the cellular environment of the host plant always dominates the regulation of Lhcb1*1 and PsbP*1 gene expression; as with the mustard system clear differences in the temporal pattern and the physiological responses could be seen. The spatio-temporal pattern of gene expression was analysed in the different organs of the transgenic tobacco seedlings. In the cotyledons, expression at the PsbP*1? promoter starts in advance, and both genes show a rather uniform distribution of expression during seedling development. In the hypocotyl, a sequential basipetal pattern could be detected and a coordinated expression for the two promoters was analysed. The hypocotyl base is only included in this expression pattern if the seedlings receive light at early stages of development, whereas in later stages gene expression is repressed. A model is proposed that divides tobacco seedling development into three main phases.