Control of Gene Expression During the Early Phase of Chloroplast Development

Abstract

Light induces changes in the expression of nuclear and chloroplast genes in higher plants [3, 4, 10, 27] and algae 13]. These alterations belong to the most impressive examples in the regulation of genes both with respect to velocity and quantity. The expression of roughly 10 to 20 prevalent mRNA’s and their correspondent proteins is regulated during this process. These effects fall into two groups. In one group the proteins and mRNA’s disappear with illumination [3, 25], whereas in the other, larger group light exerts a positive control. To the latter belong chloroplast membrane proteins like the light-harvesting chlorophyll a/b protein (LHCP) [3, 9], the 32,000 MW photogene [18, 19], as well as chloroplast stromal proteins like ribulose-1,5-bisphosphate carboxylase (RuBPCase) [28], and the isoenzmyes of chloroplast glyceraldehyde phosphate dehydrogenase (NADP·GAP·DH) [8]. These lightinducible processes involve the regulation of transcription [14] but also rather probably posttranscriptional and posttranslational events such as mRNA and protein de-gradation [4, 6, 31]. Finally, it has been also found that the assembly of membranes is under the influence of light [4, 6]. These events are presented in Fig. l for the two most impressive proteins in barley. It should be stressed, however, that there exist dramatic differences with respect to particular proteins and different species in the degree of light-dependent regulation [6, 8]; this indicates that the expression of distinct genes can be coupled to a different extent to the photoreceptors which are blue light receptors in the case of algae [29] and phytochrome primarily in higher plants [1, 2].