Light-dependent expression in liverwort cells of chlL/N and chlB identified as chloroplast genes involved in chlorophyll synthesis in the dark

Abstract

Summary Suspension cultures of both a yellow and a green cell line from the liverwort Marchantia paleacea var. diptera developed high levels of chlorophyll in the light. In the dark in organic medium, the yellow line synthesized chlorophyll but at greatly reduced levels, while the green line produced the same level of chlorophyll as that observed in the light. To elucidate the regulatory mechanism of light-independent chlorophyll synthesis in the liverwort, expression patterns of chloroplast genes were investigated. In the yellow line, levels of chlL, chlN and chlB transcripts, which have been identified as genes involved in light-independent protochlorophyllide reduction in Chlamydomonas and Plectonema, were considerably lower than those in the light. On the other hand, in the green line these genes were transcribed at the same level in the dark as in the light. In both cell lines, expression of the psaA/B genes encoding the PS-I core protein and the psbB/C genes encoding the core protein of PS-II occurred in a light-dependent manner. When the yellow line cells subcultured in the dark for 1 year were cultured in the light, the levels of both chlB and psaA transcripts increased after 3 days to the same levels as those in cells cultured continuously in the light. These results indicate that chlL/N and chlB, identified as genes involved in chlorophyll synthesis in the dark, are also photoregulated in the yellow line, while these genes in the green line are expressed in a light-independent manner.