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.) Lhcb11 and PsbP*1 genes that code for proteins related to photosystem II (PSII) in chloroplasts were ex amined by analysis of promoter fragment beta-glucuronidase (GUS) repor ter 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 e xpression characteristics for light regulation and for the influence o f a 'plastidic signal'. Hence, the cellular environment of the host pl ant always dominates the regulation of Lhcb11 and PsbP*1 gene express ion; as with the mustard system clear differences in the temporal patt ern and the physiological responses could be seen. The spatio-temporal pattern of gene expression was analysed in the different organs of th e transgenic tobacco seedlings. In the cotyledons, expression at the P sbP1? promoter starts in advance, and both genes show a rather unifor m distribution of expression during seedling development. In the hypoc otyl, a sequential basipetal pattern could be detected and a coordinat ed expression for the two promoters was analysed. The hypocotyl base i s only included in this expression pattern if the seedlings receive li ght at early stages of development, whereas in later stages gene expre ssion is repressed. A model is proposed that divides tobacco seedling development into three main phases.