Transfer RNA genes of Euglena gracilis chloroplast DNA

Summary Transfer RNA genes have been mapped to at least nine different loci on the physical map of the Euglena gracilis chloroplast genome. One of these loci in the ribosomal RNA operons is present three times per genome. The DNA sequences of six of the nine different loci, containing 21 different tRNA genes, have been determined. Genes corresponding to the amino acids Ala, Arg, Asn, Cys, Gln, Gly (2), Glu, His, Ile, Leu (2), Met (2), Phe, Ser, Thr, Trp, Tyr, Val, and one unassigned species have been identified. All genes except one are found in clusters of 2–6 genes. None of the known genes contains introns, nor codes for the 3-CCA terminus. In addition to these genes, two pseudo tRNA genes are present in the rDNA leader region.     

Transfer RNA genes associated with the 16S and 23S rRNA genes of Euglena chloroplast DNA

Hybridization studies of Euglena chloroplast ¹²⁵I-labeled tRNAs to restriction fragments of Euglena chloroplast DNA have shown that the spacer between the 16S and 23S rRNA genes, in two and possibly all three of the ribosomal DNA units, contains genes for tRNA^Ile and tRNA^Ala, whereas a tRNA gene (for either tRNA^Trp or tRNA^Glu) is located before probably all four 16S rRNA genes present on the chloroplast DNA molecule.     

Sequence of histidyl tRNA,present as a chloroplast insert in mtDNA ofZea mays

Unfractionated tRNA, isolated from maize mitochondria, has been specifically labeled at the -CCA end and used to recover a tRNA gene-bearing fragment from a clone bank of maize mitochondrial DNA. This gene has been mapped, sequenced and found to carry the anticodon for histidine. The sequence of the gene and that of bases in its near vicinity are identical to maize chloroplast tRNA^His, although sequences more distant on the fragment are not homologous with cpDNA. The junction of the cpDNA insert has been sequenced.     

Mapping of transfer RNA genes on tobacco chloroplast DNA

Tobacco chloroplast tRNAs have been purified by two-dimensional polyacrylamide gel electrophoresis, identified by aminoacylation, labelled at their 3-end and hybridized to tobacco chloroplast DNA restriction fragments, in order to establish a tRNA gene map. These hybridization studies have revealed the localization of at least seven genes in each inverted repeat region, a minimum of 22 tRNA genes in the large single copy region and one tRNA gene in the small single copy region. Comparison of the tobacco chloroplast tRNA gene map to that of maize shows many similarities, but also some differences suggesting that DNA sequence rearrangements have occurred in the chloroplast genome during evolution.     

Distribution of transfer RNA genes in thePisum sativum chloroplast DNA

Purified chloroplast tRNAs were isolated fromPisum sativum leaves and radioactively labeled at their 3′ end using tRNA nucleotidyl transferase and α³²P-labeled CTP. Pea ctDNA was fragmented using a number of restriction endonucleases and hybridized with thein vitro labeled chloroplast tRNAs by DNA transfer method. Genes for tRNAs have been found to be dispersed throughout the chloroplast genome. A closer analysis of the several hybrid regions using recombinant DNA plasmids have shown that tRNA genes are localized in the chloroplast genome in both single and multiple arrangements. Two dimensional gel electrophoresis of total ct tRNA have identified 36 spots. All of them have been found to hybridize withPisum sativum ctDNA. Using recombinant clones, 30 of the tRNA spots have been mapped inPisum sativum ctDNA.     

Zea mays chloroplast ribosomal RNA genes are part of a 22,000 base pair inverted repeat

Zea mays chloroplast rDNA exists in two identical units. Each unit contains one sequence for the 16, 23 and 5S rRNAs in the order given. The 16 and 23S sequences in each unit are separated by a 2100 base pair (bp) spacer. The DNA sequence for 5S RNA is closely linked to that for the 23S RNA. Within the above unit, the three RNAs are transcribed from a single DNA strand. The two rDNA units on the circular chloroplast DNA molecule are separated from each other by 18,500 bp in one direction and by 106,100 bp in the other direction. The two rDNA units have an inverted orientation with respect to each other. Each rDNA unit is part of a 22,000 bp sequence which is repeated with inverted orientation.     

Cellular content of chloroplast DNA and chloroplast ribosomal RNA genes in Euglena gracilis during chloroplast development.

The cellular content of chloroplast DNA in Euglena gracilis has been quantitatively determined. DNA was extracted from Euglena cells at various stages of chloroplast development and renatured in the presence of trace amounts of 3H-labeled chloroplast DNA. From the kinetics of renaturation of the 3H-labeled chloroplast DNA, compared with the kinetics of renaturation of excess nonradioactive chloroplast DNA, the fraction of cellular DNA represented by chloroplast DNA was calculated. The content of chloroplast DNA was found to increase from 4.9 to 14.6% of cellular DNA during light-induced chloroplast development. Correcting for the change in DNA mass per cell, the number of copies of chloroplast DNA is found to vary from 1400 to 2900 per cell. During this developmental transition, the cellular content of the chloroplast ribosomal RNA genes varies from 1900 to 5200 copies per cell. The ratio of the number of copies of rRNA genes to chloroplast genomes per cell remains in the range of 1-2 throughout chloroplast development, ruling out selective amplification of chloroplast rRNA genes as a means of regulation of rRNA gene expression. Direct measurement of the number of rRNA cistrons per 9.2 X 10(7) dalton genome yields a value of 1 or 2.     

Mapping of the ribosomal RNA genes on spinach chloroplast DNA.

Spinach chloroplast ribosomal RNAs have been hybridized to restriction endonuclease fragments of spinach chloroplast DNA. All three RNA species (23S, 16S and 5S) hybridized to a single large fragment when the DNA was digested with either Sall or Pstl. Hybridization of 23S RNA to fragments produced by Smal yielded two radioactive bands which corresponded to the bi-molar 2.5 X 10(6) and 1.15 X 10(6) Mr fragments. 16S RNA also hybridized to two, bi-molar Smal fragments (3.4 X 10(6) and 2.5 X 10(6) Mr) and 5S RNA hybridized to the 1.15 X 10(6) Mr bi-molar Smal fragment. The 23S RNA and 16S RNA cistrons were each also shown to contain a single EcoRI site. From the data it was possible to conclude that the ribosomal RNA genes are located on the inverted repeat region of the spinach chloroplast DNA restriction map [1,2], that the sequence of the cistrons is 16S - 23S - 5S and that the size of the spacer between the 16S and 23S RNA cistrons is approximately 0.90 X 10(6) Mr.     

Chloroplast ribosomal RNA genes in the chloroplast DNA of Euglena gracilis

Euglena chloroplast DNA has a buoyant density in CsCI of 1.686. Shearing this DNA produces a satellite band at density 1.700. The satellite, easily lost during preparative CsCI gradient centrifugation of chloroplast DNA, contains the genes for chloroplast ribosomal RNA. Pure Euglena chloroplast DNA is shown to contain one set of ribosomal RNA genes for each 90 × 10⁶ daltons of DNA.     

Gel formation on nodal root surfaces ofZea mays

Summary A gel forms profusely on the surface of nodal roots of corn. The nature and properties of the material was investigated with the purpose of understanding the mucilaginous layer which exists at the root-soil interface. Acid hydrolysis of the material revealed that it contained uronic acids, galactose, arabinose, xylose, and frucose in an approximate molecular ratio of (3:7:5:11). In addition to these sugars glucose and fructose were also present in the exudate of first or second stage nodal roots. The enzymes acid phosphatase and ATPase were present in the gel. ATPase was only slightly stimulated by K. The gel showed phosphatase activity over a broad range in pH. Contribution from the Department of Agronomy, Purdue University, Lafayette, Indiana, U.S.A. Journal Paper No. 3696 of the Purdue Agricultural Experiment Station.     

Nucleotide sequences of transfer RNA genes in the Pisum sativum chloroplast DNA

Summary Eight transfer RNA (tRNA) genes which were previously mapped to five regions of the Pisum sativum (pea) chloroplast DNA (ctDNA) have been sequenced. They have been identified as tRNA^Val(GAC), tRNA^Asn(GUU), tRNA^Arg(ACG), tRNA^Leu(CAA), tRNA^Tyr(GUA), tRNA^Glu(UUC), tRNA^His(GUG), and tRNA^Arg(UCU) by their anticodons and by their similarity to other previously identified tRNA genes from the chloroplast DNAs of higher plants or from E. gracilis. In addition,two other tRNA genes, tRNA^Gly (UCC) and tRNA^Ile(GAU), have been partially sequenced. The tRNA genes are compared to other known chloroplast tRNA genes from higher plants and are found to be 90–100% homologous. In addition there are similarities in the overall arrangement of the individual genes between different plants. The 5 flanking regions and the internal sequences of tRNA genes have been studied for conserved regions and consensus sequences. Two unusual features have been found: there is an apparent intron in the D-loop of the tRNA^Gly(UCC), and the tRNA^Glu(UUC) contains GATTC in its T-loop.     

Transfer RNA gene mapping studies on chloroplast DNA from Chlamydomonas reinhardii

Total tRNA of Chlamydomonas reinhardii was fractionated by 2-dimensional gel electrophoresis. Sixteen tRNAs specific for eleven amino acids could be identified by aminoacylation with Escherichia coli tRNA synthetases. Hybridization of these tRNAs with chloroplast restriction fragments allowed for the localization of the genes of tRNA^Tyr, tRNA^Pro, tRNA^Phe (2 genes), tRNA^Ile (2 genes) and tRNA^His (2 genes) on the chloroplast genome of C. reinhardii. The genes for tRNA^Ala (2 genes), tRNA^Asn and tRNA^Leu were mapped by using individual chloroplast tRNAs from higher plants as probes.     

Expression of genes for cell-wall proteins in dividing and wounded tissues ofZea mays L.

Hydroxyproline-rich glycoproteins (HRGPs) fromZea mays have been immunolocalized in the cell wall of root tip cells using ultrathin sections and antibodies ellicited against the purified protein. The accumulation of mRNA corresponding to this protein was studied using the cDNA probe. Maximum accumulation of the mRNA was found in tissues with a high proportion of dividing cells such as those in the root tip of young maize seedlings and a close relationship with cellular division was also observed in in-vitro cultures. However, the level of the mRNA in elongating tissues was minimal, as shown by studies carried out on the elongation zones of root tips and coleoptiles. The mRNA was induced by stress conditions, particularly by wounding young leaves and coleoptiles. It is concluded that in maize this group of proline-rich cell-wall proteins accumulates during cell division and not during cell elongation or differentiation, and participates in the stress-response mechanisms of the plant.     

Sequencing of the 16S-23S spacer in a ribosomal RNA operon of Zea mays chloroplast DNA reveals two split tRNA genes

The nucleotide sequence of th 16S-23S spacer from a ribosomal RNA operon of Zea mays chloroplast DNA has been determined. It contains two tRNA genes, coding for tRNAlle (AUCU) and tRNAAla (GCGA), which are split by intervening sequences of 949 and 806 base pairs, respectively. Homology between the two introns suggests that they have a common origin.     

Arrangement of the ribosomal RNA genes in chloroplast DNA of Leguminosae

Summary The circular chloroplast DNA from three species of plants in the taxonomic family Leguminosae were examined using electron microscopic techniques and restriction endonuclease digestion. Chloroplast DNAs from chickpea (Cicer arietinum), mung bean (Vigna radiata), and soy bean (Glycine max) were found to range in size from 119–151 kilobase pairs by contour length measurements. Sizes of the chloroplast DNAs have been further confirmed using different restriction endonucleases. Two of the chloroplast DNAs examined, soy bean and mung bean, contain a region approximately 15.9–18% of their monomer length that is repeated in reverse polarity. This repeated region separates a small unique region that ranges in size from 18.75–20.4 kilobase pairs and a large unique region that ranges in size from 73.4–85 kbp. This feature was not found in the chloroplast DNA of chickpea. R-loop hybridizations performed using chloroplast ribosomal RNAs demonstrate that the two ribosomal gene sets of the mung been and soy bean are arranged in inverted orientation within this repeated region. In contrast, the chickpea chloroplast DNA posesses a single ribosomal RNA gene set in the circular molecule. In all three chloroplast DNAs examined, the genes encoding the chloroplast 23S and 16S ribosomal RNA genes are separated by a spacer region which ranges in size from 2.2 to 2.48 kbp.     

Response ofZea mays roots to infection withPhytophthora cinnamomi

Summary Zea mays is a non-host ofPhytophthora cinnamomi; plants survive contact with this fungus both in the field and in pot trials. TheZ. mays-P. cinnamomi interaction has been studied by light and electron microscopy. In the epidermal layer, fungal hyphae grow intercellularly through the middle lamella. This is always the case for the first hyphal contact with any cell. Hyphae making second or subsequent contacts with a cell grow preferentially between the cell wall and plasma membrane of the infected cell rather than through the middle lamella.Papillae (callose deposits) are formed in response to some, but not all, regions of contact between the plant cell and the hypha. They do not completely encase the hypha and do not stop hyphal growth. The plasma membrane-cell wall interface of the host cell must be intact for effective papilla formation, as papillae are rarely formed when the hyphae grow between the plasma membrane and the cell wall.