INTRON SEQUENCES ARE INVOLVED IN THE PLASTID-DEPENDENT AND LIGHT-DEPENDENT EXPRESSION OF THE SPINACH PSAD GENE

Plastid- and light-regulated expression of the spinach PsaD gene in tr ansgenic tobacco requires sequences downstream of the transcription st art site, and promoter sequences alone are not sufficient to respond t o these stimuli. The spinach PsaD mRNA level in transgenic tobacco is still plastid- and light-responsive when the expression of the intron- containing transcription unit is driven by the 35S RNA CaMV promoter i ndicating that PsaD contains (a) gene-internal control element(s). If the genomic PsaD sequence in the latter construct was replaced by the cDNA, a constitutive expression of the PsaD transcript level was obser ved. It is concluded that the intron sequence contributes to the plast id- and light-dependent expression of the spinach PsaD gene.