Photosynthetic electron transport differentially regulates the expression of superoxide dismutase genes in liverwort, Marchantia paleacea var. diptera.

Liverwort, Marchantia paleacea var. diptera, contains Mn-superoxide dismutase (Mn-SOD) in mitochondria, Fe-SOD in chloroplast and CuZn-SOD in cytosol. An Mn-SOD gene (MpMnSOD) was isolated from the liverwort. Using this clone together with the liverwort Fe-SOD and CuZn-SOD genes as probes, the expression of three SOD genes was investigated. Under heterotrophic conditions, the transcript of three SOD genes was accumulated light independently. On the other hand, under photoautotrophic conditions, the transcript levels of Fe-SOD and Mn-SOD increased in the light while that of CuZn-SOD decreased. The reverse occurred in the dark. In contrast to the transcript level, the activity of the three SODs was barely affected by light. The transcription inhibitor, cordycepin, inhibited either the light-promoted accumulation of Fe-SOD and Mn-SOD transcript or the light-induced reduction of the CuZn-SOD transcript. Photosynthetic electron transport inhibitors, DCMU and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, inhibited the photo-response in three SOD genes. These results suggest that the transcript abundance of three SOD genes in liverwort is regulated by photosynthetic electron transport but the mechanism regulating the transcript abundance of the CuZn-SOD gene is different from that of the Fe-SOD and Mn-SOD genes.