Regulation of 7S globulin gene expression in zygotic and somatic embryos of oil palm

We describe here the characterization and expression analysis of the oil pa lm GLO7A gene encoding a 7S globulin protein. Previous work carried out in our laboratory showed that 7S globulins accumulate in the oil palm zygotic embryo mostly between the 14 and 17 weeks after pollination. To investigate further the regulation of 7S globulin gene expression in both zygotic and somatic embryos of oil palm, we isolated a cDNA clone, GLO7A, for use as a probe in northern hybridization studies. The nucleotide sequence of the GLO 7A cDNA reveals that it encodes a polypeptide of 572 amino acids (66 kDa) s haring significant sequence similarities with various vicilin-like proteins of both dicotyledonous and monocotyledonous plants. Northern hybridization analysis shows that 7S globulin mRNA accumulation in zygotic embryos is te mporally regulated with a profile essentially the same as that observed at the protein level. In somatic embryos, 7S globulin proteins were found to o ccur in amounts approximately 80 times lower than those in zygotic embryos. This lack of 7S globulin protein accumulation in somatic embryos is mirror ed by a low accumulation of the GLO7A mRNA, The in vitro production of 7S g lobulins (and more generally salt-soluble proteins) is improved by the addi tion to the culture medium of arginine, sucrose and ABA, the effects of the se 3 components being additive. To investigate further the action of the 3 molecules of interest, we performed parallel studies on mRNA and protein ab undance. Our studies of transcript accumulation suggest that ABA and sucros e act directly on mRNA synthesis or stability; however, it appears that the re are also translational or post-translational regulatory factors which ac t to limit protein accumulation in somatic embryos. The GLO7A gene promoter was cloned and sequenced to assess whether GLO7A gene expression might be modulated by cis-acting promoter elements related to those found in other p lants. Two motifs resembling ABREs (ABA-responsive elements) and one motif resembling a seed-specific promoter element were identified within the 5 ' flanking sequence.