Abstract
Amyloplast is a subtype of plastids found in non-photoshynthetic tissues characterized by starch synthesis and storage. Tobacco BY-2 cultured cell is normally grown in an auxin-medium, and exchanging hormone from auxin to cytokinin induces differentiation of proplastid to amyloplast. In this system, expression of nuclear genes such as ADP-glucose pyrophosphatase(Agp), which are required for starch biosynthesis, are induced. However, involvement of plastid gene expression in amyloplast differentiation remains unclear.
We here examined plastid gene expression by northern analysis, and found that no major change during amyloplast differentiation was observed. Nevertheless, starch biosynthesis followed by amyloplast development was inhibited in the presence of plastid translation/transcription inhibitors, spectynomycin or rifampicin. Interestingly, we found that expression of nuclear-encoded starch biosynthesis genes such as Agp was repressed by addition of these inhibitors. These results suggest that plastid transcription/translation is required for amyloplast development via unknown signals regulating nuclear gene expression.
