pSAS10

A novel dehydrin gene (VrDhn1) was isolated from an embryo cDNA library of Vigna radiata (L.) Wilczek (mungbean) variety VC1973A. The intronless VrDhn1 gene encodes a protein belonging to the Y(2)K-type dehydrin family. VrDhn1 protein accumulated in embryos and cotyledons during seed maturation and disappeared 2 days after seed imbibition (DAI). The expression of VrDhn1 mRNA and accumulation of VrDhn1 protein were at high levels in mature seeds, but neither mRNA nor protein was detected in mungbean vegetative tissues under normal growth conditions. The VrDhn1 mRNA level was extremely high in mature seeds and decreased to ~30% at 1 DAI, and was not detectable at ~7 DAI. Tissue dehydration, salinity and exogenous ABA markedly induced VrDhn1 transcripts in plants as measured by quantitative real-time reverse transcription-PCR (qRT-PCR). VrDhn1 protein was not detected using immunoblots in seedlings under stress treatments. In mature seeds or 1 DAI seedlings, VrDhn1 proteins were immunolocalized in the nucleus and cytoplasm. VrDhn1 exhibited low affinity for non-specific interaction with DNA using electrophoretic mobility shift assays (EMSAs), and the exogenous addition of Zn(2+) or Ni(2+) stimulated interaction. The His-tagged VrDhn1 (30.17 kDa) protein showed a molecular mass of 63.1 kDa on gel filtration, suggesting a dimer form. This is the first report showing that a Y(2)K-type VrDhn1 enters the nucleus and interacts with DNA during seed maturation.

Proteinase A is a papain-like cysteine endopeptidase of vetch (Vicia sativa L.) which was assumed to initiate storage-globulin breakdown just after the onset of seed germination. This enzyme was purified from cotyledons of vetch seedlings. On gelatin-containg SDS gels, active proteinase A migrated with an apparent molecular mass of 21 kDa, whereas after heat denaturation its molecular size on SDS/PAGE was 29 kDa. Although proteinase A is capable of hydrolyzing storage globulins in vitro it could not be localized in the protein-body fraction of cotyledons from germinating seeds. cDNA clones encoding proteinase A precursor have been obtained by PCR. The precursor is composed of an N-terminal signal sequence followed by a propeptide, the region encoding mature proteinase A, and a C-terminal KDEL sequence. Mature proteinase A with a derived molecular mass of 25,244 Da does not have the KDEL sequence. The derived amino acid sequence of the proteinase A precursor is 78.2% identical to sulfhydryl-endopeptidase (SH-EP), a cysteine endopeptidase from germinating Vigna mungo seedlings. Northern blot analysis indicated that proteinase A mRNA appears de novo in cotyledons of 1-day-germinated vetch seeds, where its amount increases up to day 6. No proteinase A mRNA was detected in other vetch organs, not even in the embryo axis, which contains stored globulins. By means of antibodies raised against the purified and against recombinantly produced proteinase A, the 29-kDa bands of mature proteinase A were detected in cotyledon extracts of 6-day-germinated seeds when globulin degradation has already far proceeded. The reported data do not agree with the proposed triggering role of proteinase A in storage-globulin breakdown during germination.

A complementary DNA (cDNA) library has been constructed in lambda gt 10 from poly(A)+ mRNA isolated from auxin-deprived strawberry receptacles. By differential plaque filter hybridization, a cDNA (lambda SAR5) to an auxin-repressed mRNA has been isolated. The expression of the auxin-repressed gene is studied at various stages of normal fruit development and in fruits of variant strawberry genotype using lambda SAR5 as a probe. Northern analyses of RNA isolated from pollinated and unpollinated fruits of various developmental stages revealed that mRNA corresponding to the lambda SAR5 clone is repressed during normal fruit development, and the level of lambda SAR5 mRNA is regulated by endogenous auxin. Furthermore, results with both normal and variant genotype strawberry fruit indicate that there is a positive correlation between growth of strawberry fruit and repression of mRNA corresponding to the lambda SAR5 clone. The lambda SAR5 cDNA has been sequenced and is 723 nucleotides in length. The deduced protein has 111 amino acid residues with a molecular mass of 12.5 kDa. The putative polypeptide starts at nucleotide position 20 and ends at 352. The molecular weight of the predicted polypeptide is in agreement with the molecular weight of the in vitro translated polypeptide of hybrid selected mRNA. A comparison of the nucleotide and deduced amino acid sequence of lambda SAR5 with nucleotide and protein sequences in data banks has not revealed any homology to known proteins.