Searching for mechanisms leading to albino plant formation in cereals

Microspore embryogenesis is a method of great importance for plant production in many species. Its practical use in monocotyledonous plants, however, is limited due to the occurrence of albino plants. Molecular examinations of such albino plants showed an aberrant form of plastids and, frequently, deletions in their plastid DNA. Moreover, in Our preceding work we found typical deficiencies in plastid transcription and translation. Nevertheless, there are also indications for an involvement of the nuclear genome in albino plant formation. To address these questions, we characterised, on the one hand, a plastid factor, which is possibly involved in the formation of plastid DNA deletions, and investigated, on the other hand, nuclear gene expression in albino plants. The Ycf1 gene is present in the plastid genomes of dicots, while monocots only have a truncated pseudogene. The disruption ycf1 in tobacco showed that it is essential for the survival of dicotyledonous plants. In addition, we replaced the tobacco ycf1 by the pseudogene of rice and found rearrangements in the plastid genomes of the resulting plants indicating that the ycf1 locus plays a role in the stability of plastid DNA. The study on nuclear gene expression showed that there is an extensive alteration of transcript levels in albino plants. We found that the respective genes encode proteins with a broad range Of functions in plants. All these findings taken together suggest that albino plant formation is a complex phenomenon in which both, plastid and nuclear factors or their defective interactions are involved.