Light-independent developmental regulation of cab gene expression in Arabidopsis thaliana seedlings.

We found a transient increase in the amount of mRNA for four nuclear genes encoding chloroplast proteins during early development of Arabidopsis thaliana. This increase began soon after germination as cotyledons emerged from the seed coat; it occurred in total darkness and was not affected by external factors, such as gibberellins or light treatments used to stimulate germination. Three members of the cab gene family and the rbcS-1A gene exhibited this expression pattern. Because timing of the increase coincided with cotyledon emergence and because it occurred independently of external stimuli, we suggest that this increase represents developmental regulation of these genes. Further, 1.34 kilobases of the cab1 promoter was sufficient to confer this expression pattern on a reporter gene in transgenic Arabidopsis seedlings. The ability of the cab genes to respond to phytochrome preceded this developmental increase, showing that these two types of regulation are independent. IMAGES: