On the nature of the polymorphism of the small subunit of ribulose-1,5-diphosphate carboxylase in the amphidiploid Nicotiana tabacum

The structure and regulation of homeologous tobacco endochitinase genes of Nicotiana sylvestris and N. tomentosiformis origin

The fungicidal class I chitinases are believed to be important in the induced defense response of plants. We isolated and partially characterized genomic clones representing two members, CHN14 and CHN50, of the gene subfamily encoding these enzymes in Nicotiana tabacum L. cv. Havana 425. The coding sequences of genes CHN14, CHN50, and CHN48, which was cloned earlier, are identical at 79-95% of the positions. Tobacco is an amphidiploid species derived from ancestors most closely related to the present-day species N. sylvestris and N. tomentosiformis. Southern analysis of genomic DNA, comparison of deduced amino acid sequences, and partial sequencing of the purified enzymes suggest that the gene pairs CHN48/CHN50 and CHN14/CHN14' are homeologues. Gene CHN48, which encodes chitinase A (Mr ca. 34 kDa), and gene CHN14 are derived from N. tomentosiformis; whereas gene CHN50, which encodes chitinase B (Mr ca. 32 kDa), and gene CHN14' are derived from N. sylvestris. Class I chitinases are induced in leaves of plants treated with ethylene or infected with the fungal pathogen Cercospora nicotianae and in cultured cells transferred to medium without added auxin and cytokinin. RNase protection assays show that under these conditions transcripts encoded by the homeologues CHN48 and CHN50 account for greater than 90% of the total chitinase mRNA. The less abundant transcript, CHN48, consistently showed a greater degree of induction than CHN50. Expression of the homeologues CHN14 and CHN14' represented less than 10% of the total chitinase mRNA. They showed a pattern of hormonal regulation similar to CHN48 and CHN50, but transcripts of these genes were not detected in leaves infected with C. nicotianae. Therefore the two sets of homeologues are regulated in the same way by hormones and respond differently to infection by a pathogen.

Absence of some truncated genes in the amphidiploid Nicotiana tabacum

As an initial step towards understanding how a multigene family evolves after an interspecific hybridization and subsequent chromosomal doubling, genomic Southern blots of three related species were compared: Nicotiana tabacum (the progeny), and Nicotiana sylvestris and Nicotiana tomentosiformis (the progenitors). Genomic restriction fragments generated by two endonucleases were hybridized with a cDNA of the small subunit of ribulose bisphosphate carboxylase from N. sylvestris. The restriction pattern of the DNA of the progenitors revealed considerable polymorphism of restriction-fragment lengths. All the fragments in N. tabacum, except one, have a corresponding fragment in one of the progenitors. Some fragments present in the parents were absent from the progeny: they may correspond to truncated genes consisting of only part of the 3' portion of the gene.

A simple gene-expression system for the small subunit of ribulose bisphosphate carboxylase in leaves ofNicotiana sylvestris

InNicotiana sylvestris only four transcripts coding for the small subunit of RUBISCO are present in leaves. They are very closely related as they are identical in the nucleotide sequence of the non-coding regions and show only three silent point differences in the region coding for the mature peptide.The main difference among these four transcripts lies in the length of the non-coding regions. Half of the SmRNA population as confirmed by direct RNA sequencing has an additional nucleotide sequence in the leader region. Two cDNAs have an additional nucleotide sequence at the end of the 3' non-coding region. Based on these criteria the transcripts were classified into two groups:.group I has a 73-nucleotide-long leader sequence and the nucleotides T, A and C at position 327, 432 and 519 in the coding region..group II has a 60-nucleotide-long leader sequence and the nucleotides C, G and T at these positions in the coding region.The two cDNAs showing a difference in the length of the 3' non-coding region belong to group II.The study of all these transcripts argues for the possibility that only two families of genes are expressed in leaves ofN. sylvestris.

Complete sequence of one of the mRNAs coding for the small subunit of ribulose bisphosphate carboxylase of Nicotiana sylvestris

The combination of cDNA and RNA sequencing techniques has enabled determination of the complete sequence of one of the mRNAs coding for the precursor of the small subunit of ribulose bisphosphate carboxylase of Nicotiana sylvestris. In this 898-nucleotide-long mRNA, 540 nucleotides code for the entire 180-amino-acid-long precursor polypeptide consisting of the 57-amino acid-long transit peptide and the 123-amino-acid-long mature protein, while 60 and 195 nucleotides belong to the 5' and 3' noncoding flanking regions, respectively. The 5' end, which is very rich in AG residues, contains several direct and indirect repeated sequences, and a possible hairpin structure. The 3' end, terminated by a 103-nucleotide-long poly-A tail, is very rich in AU residues but does not contain the classical polyadenylation signal sequence.

Analysis of catalytic subunit microheterogeneity in ribulosebisphosphate carboxylase/oxygenase from Nicotiana tabacum

Urea isoelectric focusing of dissociated, carboxymethylated Nicotiana tabacum ribulose-1,5-bisphosphate carboxylase/oxygenase reveals catalytic subunit microheterogeneity. Aggregated or nonaggregated sucrose gradient-purified preparations and the crystalline protein displayed essentially identical large subunit multiple polypeptide patterns. Various pretreatments which fully dissociate the holoenzyme did not alter catalytic subunit microheterogeneity. Direct comparison of the carboxymethylated and noncarboxymethylated crystalline and sucrose gradient-purified proteins demonstrated that the large subunit multiple polypeptide pattern was not an artifact of carboxymethylation. The inclusion of the seryl protease inhibitor phenylmethylsulfonyl fluoride during purification of the holoenzyme did not affect the large subunit multiplicity. However, the addition of leupeptin, a potent thiol proteinase inhibitor, to all solutions during purification of the native protein markedly reduced large subunit polypeptide L3 and increased the staining of polypeptide L2, suggesting that L3 is a leupeptin-sensitive proteinase degradation product of L2. Polypeptide L1 also appeared to be a purification-related artifact, but derived from a modification of L2 other than that which yielded L3. We conclude that polypeptide L2 is the single, native isoelectric form of the catalytic subunit of tobacco ribulosebisphosphate carboxylase/oxygenase.

Two dimensional analysis of chloroplast proteins from normal and cytoplasmic male sterile Brassica napus

Stromal and thylakoid proteins isolated from normal (N) and cytoplasmic male sterile (cms) lines of Brassica napus have been compared using a two dimensional gel separation. It has been shown that: 1) stromal compartments of the two lines were very similar; 2) although there was extensive homology between protein maps of thylakoids isolated from the two lines, these could be distinguished by the spots corresponding to the β subunits of the coupling factor CF1 from the ATPase complex.

Inheritance behavior of information coding for small subunit polypeptides of fraction 1 protein

In various genera of plants, the small subunit of fraction 1 protein is often composed of more than one kind of polypeptide; these differ in isoelectric points and amino acid composition. Previous analysis of numerous individual progeny of Nicotiana tabacum (two kinds of polypeptides), N. glauca + N. langsdorffii parasexual hybrids (three kinds) and other examples showed no change in F-1 protein composition as a consequence of alternation of generations. Experiments reported here show that absence of one number of each of the 24 different pairs of chromosomes in an N. tabacum monosomic series and also absence of the "S" pair in a nullisome did not affect F-1 protein composition. Absence of the "E" pair caused reduction in the amount of the least acidic of the two kinds of N. tabacum small subunit polypeptides. The question of how many individual progeny of self-fertile hybrids would have to be analyzed to detect segregation of genes coding for F-1 protein small subunit polypeptides, if segregation occurs, was answered by analysis of F1 hybrids between N. otophora and N. tomentosiformis, and two subspecies of N. suaveolens, together with their F2 progeny. In both cases, analysis of 16 progeny was sufficient to demonstrate a segregation pattern of two F1 hybrid type to one each of the two parental types. Therefore, in the absence of segregation, it is likely that coding information for different kinds of F-1 protein small subunit polypeptides is sequestered on heterologous chromosomes, as postulated in previous reports.

Nicotiana Chromosome Coding for a Specific Polypeptide of the Small Subunit of Fraction 1 Protein

Fraction 1 protein has been isolated from leaves of a male sterile Nicotiana tabacum plant containing an extra N. debneyichromosome. The extra chromosome induces appearance of a third polypeptide composing the small subunit of fraction 1 protein, which otherwise contains two polypeptides as is shown by analysis of numerous different cultivars of N. tabacum.

Evolution of fraction 1 protein in the genus Lycopersicon

The large- and small-subunit polypeptide composition of fraction 1 protein contained in seven species of Lycopersicon and Solanum pennellii was determined by electrofocusing. The eight species of protein had large subunits composed of three polypeptides separated by about 0.05 pH unit, but there was no difference in the isoelectric points of the clusters of three polypeptides. By this criterion, no surviving mutations have appeared in the extranuclear DNA coding for the cluster of large-subunit polypeptides during a period of evolution which generated the eight species of plants. The genus Lycopersicon appears to be much younger than its sister genus Nicotiana in the family Solanaceae, where four types of polypeptide clusters have evolved. Three different small-subunit polypeptides whose isoelectric points are coded by nuclear DNA have arisen among the seven Lycopersicon species, and L. hirsutum and S. pennellii have proteins containing single polypeptides and are therefore considered older than L. chilense, L. chimielewskii, and L. parviflorum, whose proteins contain two polypeptides. L. cheesemanii, L. pimpinellifolium, and L. esculentum (and probably L. peruvianum) seem to be the most recently evolved species since their fraction 1 proteins have small subunits composed of three polypeptides.

Isolation, characterization, and crystallization of ribulosebisphosphate carboxylase from autotrophically grown Rhodospirillum rubrum

Serial culture of Rhodospirillum rubrum with 2% CO2 in H2 as the exclusive carbon source resulted in a rather large fraction of the soluble protein (greater than 40%) being comprised of ribulosebisphosphate carboxylase (about sixfold higher than the highest value previously reported). Isolation of the enzyme from these cells revealed that it has physical and kinetic properties similar to those previously described for the enzyme derived from cells grown on butyrate. Notably, the small subunit (which is a constituent of the carboxylase from eucaryotes and most procaryotes) was absent in the enzyme from autotrophically grown R. rubrum. Edman degradation of the purified enzyme revealed that the NH2 terminus is free (in contrast to the catalytic subunit of the carboxylase from eucaryotes) and that the NH2-terminal sequence is Met-Asp-Gln-Ser-Ser-Arg-Tyr-Val-Asn-Leu-Ala-Leu-Lys-Glu-Glu-Asp-Leu-Ile-Ala-Gly-Gly-Glx-His-Val-Leu-. Crystals of the enzyme were readily obtained by dialysis against distilled water.

Ribulose-1,5-bisphosphate carboxylase as a nuclear and chloroplast marker

The data on the primary structure of ribulose-1,5-bisphosphate carboxylase/oxygenase are reviewed. Examples of their use as markers and in the elucidation of the evolution, adaptation and function of this key enzyme are given.