Expression of two cloned mRNA sequences during development and germination of spores of the sensitive fern, Onoclea sensibilis L.

A library of complementary DNA (cDNA) clones has been prepared from poly(A)+RNA of spores of the sensitive fern, Onoclea sensibilis L. By differential hybridization with labeled probes made to poly(A)+RNA of spores, gametophytes and leaves, two spore-specific clones (pOSS68 and pOSS194) were selected and characterized. Northern blot analysis showed that RNA sequences homologous to the two cDNA clones first appear in the post-meiotic spore and increase in abundance during spore maturity. Both RNA sequences decay during photoinduced germination of the spores and do not reappear in the gametophytes. In spores imbibed in the dark under conditions which do not favor germination, no significant decrease in pOSS194-mRNA abundance is noted. In contrast, the decrease in pOSS68 mRNA in dark-imbibed spores parallels that observed in photoinduced spores. The predicted amino-acid sequence of pOSS194 has a striking similarity to the early light-inducible proteins expressed during the greening of etiolated pea and barley seedlings, whereas that of pOSS68 shows some homology to proteins encoded by late-embryogenesis-abundant mRNAs of angiosperm embryos.