| Research Abstract |
I.We have succeeded in cloning the plastid genes, chlL and chlN,which are required for the light -independent biosynthesis of chlorophyll from two ferns (Pteridium aquilium and Adiantm capillus-veneris) and two conifers (Pinus thunbergii and Larix Kaempferi), and have determined their nucleotide sequences. (1) For Adiantum and Pteridium, we found out the possibility that RNA editing, a post-transcriptional process is necessary for correct expression of both the two chl genes. Isolation of RNA from Pteridium leaves and subsequent sequencing of the chlL cDNA revealed that the transcript encoded by chlL gene are post-tanscriptionally subject to extensive editing. (2) In coniferous plants, pine seedling is capable of light-independent biosynthesis of chlorophyll while larch seeding is incapable. However, sequence analysis showed that larch, as well as pine, has the homolog of chlL and chlN gene, respectively.
II.We have examined the transcription level of chlL and chlN genes in the fern protonemata and the conifer seedlings by northern blot analysis. (1) In dark-grown protonemata of Adiantum and Pteridium, each of the two chl genes was found to be transcribed as is the case of the light-grown protonemata. Each transcript had the size which was predictable from the coding region. The accumulation level of the transcripts in the dark were undistinguishable from those in the light. The similar results were obtained for pine seedlings. (2) For yellowish dark-grown seedlings of larch, we found that both the two chl genes were expressed to the same extent as for the green light-grown seedlings. In the dark-grown larch, however, the size of chlL transcript was remarkably larger than its expected size, whereas two different sizes of chlN transcript were detected. The presence of larger transcripts of chlL and chlN may be attributed to the lack of processing activity of polycistronic transcripts in larch plastide.
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