DIFFERENTIALLY REGULATED GENE SETS IN DOUGLAS FIR SEEDS AND SOMATIC EMBRYOS. SANTOSH MISRA, MALINEE CHATIHAI, TIMOTHY J. TRANBARGER, BENJAMIN S. FORWARD, AND KARIA H. KAUKINEN Department of Biochemistry and Microbiology University of Victoria. Victoria. B.C. V8W 3P6. ABSTRACT. Differential screening of cDNA libraries of mid-maturation stage zygotic embryo 4-6 day old seedlings yielded a set of cDNAs preferentially expressed during embryogenesis and germination, respectively. Sequence analysis of embryo cDNAs identified these clones as ena isoforms of 2S storage proteins- albumins, and an MT -like protein. The expression of these ger different stages of zygotic and somatic embryogenesis was examined by Northern blot analysis different patterns of expression were observed for various isoforms of albumins. The MT-like gem expressed in embryos and needles and its expression was regulated by ABA, osmoticum as well as I ions. Partial DNA sequence analysis and predicted amino acid sequences of germination - IlSSO( cDNAs show we have isolated clones with homology to a range of plant proteins: including a chape 60-P, low molecular weight heat shock proteins (LMW HSPs), a luminal binding protein (BiP), a 1) chlorophyll alb binding protein (CAB), a thiol-protease precursor and a NADPH-P450 reductase. I seeds all the clones detected transcripts which increased by 2 days of germination. 1 . Introduction Seed development and germination are distinct metabolic events in which the status of storage pre contrast markedly and hence provide a model system to investigate the regulation of gene exprel Desiccation, an essential part of normal seed development, may activate genes for germination an( off the synthesis of embryogenesis related proteins. Several studies have revealed the presence of m in mature seed tissues, referred to as stored mRNA. which may be immediately available on rehydJ for translation of the proteins required for germination (Bewley and Marcus, 1990). Imbibition of II dormant seeds leads to the appearance of new and temporally distinct sets of mRNAs and gene pre that are absent in mature seeds (reviewed by Lane, 1991). Several of these gene products are involv the transformation of storage compounds into energy and anabolic substrates for germination (Bewle Marcus, 1990). Examples include enzymes of the glyoxylate cycle and enzymes involved in st product mobilization and nitrogen assimilation (reviewed in Bewley and Marcus, 1990). The storage tissue in conifer seeds is the haploid, maternally derived megagametophyte. In conta angiosperm storage tissues that originate and develop after fertilization, the megagametophy Douglas-fir and other conifers is fully developed before fertilization. Storage protein accumulation i megagametophye and the embryo starts during early and mid embryogenesis, repectively, and termi during the desiccation phase of seed maturation (Owens et al., 1993; Misra, 1994). During germin: proteins are mobilized from the megagametophyte to provide free amino acids to the embryo. elucidate the regulatory mechanisms involved in the expression of genes during germination and early seedling development of conifer seeds, we have initiated studies on the clomn characterization of developmentally regulated gene sets. We report here the cloning and analysis of of cDNAs from a Douglas-fir embryogenesis and germination-specific libraries. Northern blot an showed that these mRNAs are differentially expressed during zygotic embryogenesis. germinatio early seedling development The temporal expression pattern of genes in somatic embryos paralle observed in zygotic embryos indicating that somatic embryos may provide a useful system to fae studies of gene regulation in conifers. 197 M. R. Ahuja et al. (eds.), Somatic Cell Genetics and Molecular Genetics a/Trees, 197-204. © 1996 Kluwer Academic Publishers.