Vladimir A. Berdnikov

Histone H1 of the garden pea (Pisum sativum L.) ; composition, developmental changes, allelic polymorphism and inheritance

Abstract Histone H1 of the garden pea ( Pisum sativum L. ), as a rule, is represented by seven subtypes, as revealed by the high resolution acetic acid/urea polyacrylamide gel electrophoresis. Each subtype has molecular variants differing in the electrophoretic mobility and is encoded by a single gene. Gene His1 , coding for the slowest subtype 1, was mapped on chromosome 5. A complex locus His(2–6) , containing closely linked genes encoding subtypes 2 to 6, and the gene His7 of the subtype 7 were mapped on chromosome 1, with the distance of approximately 30 cM between them. Histone H1 spectrum changes during the maturation of tissues: subtype 7 is relatively abundant in all young tissues and gradually disappears in the course of their maturation, while the relative amount of subtype 6 increases. Several other legume species tested have H1 spectra homologous to that of the garden pea.

Adaptive Nature of Interspecies Variation of Histone H1 in Insects

SummaryAn electrophoretic analysis of histone H1 and its fragments was carried out for several orders of insects. A total of more than 500 histone H1 variants were examined. For some of them a study of general molecular structure was performed by the method of incomplete succinylation. The molecular length of the fragment containing the C-terminal domain presumably responsible for chromatin condensation was found to be highly variable. The variance of the logarithm of the electrophoretic mobility of H1, which reflects its molecular length, was estimated for seven insect orders. There was no relationship between this variance and the evolutionary age of an order. On the other hand, the variance turned out to correlate strongly with the recent species number in the order, indicating that the accumulation of variation in H1 molecular length was in line with the general intensity of adaptive processes in the orders. This result seems to provide evidence for an adaptive mode of the evolution of the molecular length of H1. The possible role of H1 variability in adaptive evolution is discussed.

Large changes in the structure of the major histone H1 subtype result in small effects on quantitative traits in legumes

Electrophoretic analysis of the most abundant subtype of histone H1 (H1-1) of 301 accessions of grasspea (Lathyrus sativus) and 575 accessions of lentil (Lens culinaris) revealed allelic variants which most probably arose due to recent mutations. In each species, a single heterozygote for a mutation was taken for construction of isogenic lines carrying different H1-1 variants. Sequencing of alleles encoding H1-1 in lentil, grasspea, pea and Lathyrus aphaca showed the presence of an extended region in C-terminal tail which we termed ‘regular zone’ (RZ). It consists of 14 6-amino-acid units of which 12 (pea and Lathyrus species) or 13 (lentil) are represented by an AKPAAK sequence. The structure of the hypervariable unit 8 is species-specific. At the DNA level most AKPAAK units differ in the third codon positions, implying the action of natural selection preserving the RZ organization. In lentil, the fast variant lost two units (including unit 8), while one AKPAAK repeat of the slow variant is transformed into an anomalous SMPAAK. The mutant variant of the grasspea H1-1 differs from the standard one by duplication of an 11-amino-acid segment in N-terminal tail. The isogenic lines of lentil and grasspea were compared for a number of quantitative traits, some of them showing small (1–8%) significant differences.

Phenotypic effect of substitution of allelic variants for a histone H1 subtype specific for growing tissues in the garden pea (Pisum sativum L.)

In pea, subtype H1-7 of histone H1 is specific for young actively growing tissues and disappears from chromatin of mature tissues. We sequenced the alleles coding for three main variants, numbered according to the increase of the electrophoretic mobility. Allele 1 differs from the most common allele 2 by eight nucleotide substitutions, two of them associated with amino acid replacements, His->Tyr in the globular domain and Ala->Val in the C-terminal domain. Allele 3 differs from alleles 1 and 2 by a 24-bp deletion in the part coding for the C-terminal domain. In three greenhouse experiments, we compared quantitative traits in nearly isogenic lines differing by these H1-7 variants. In experiment 1, three lines bearing either of the three allelic variants were compared, the other experiments involved pairs of lines bearing variants 1 and 3. In all experiments, statistically significant differences between the lines were registered, mostly related to the plant size. The most prominent effect was associated with plant growth dynamics. Plants of line 3, carrying the 8-amino acid deletion in histone H1-7, on average grew slower. In two experiments, the differences of the mean stem length persisted throughout plant growth while in experiment 2 differences disappeared upon maturity. The H1-7 subtype is supposed to be related to maintenance of chromatin state characteristic for cell growth and division.

Evolution of the regular zone of histone H1 in Fabaceae plants

An analysis of the histone H1 subtype, H1-1, in eight legumes belonging to four genera of the tribe Vicieae (Pisum, Lathyrus, Lens, and Vicia), revealed an extended region consisting of the tandemly repeated AKPAAK motifs. We named this region the Regular zone (RZ). The AKPAAK motifs are organized into two blocks separated by a short (two or six amino acids) intervening sequence (IS). The distal block contains six AKPAAK motifs, while the number of repeats in the proximal block varies from six in V. faba to seven in the other species. In V. hirsuta, the first two repeated units of the proximal block are octapeptides AKAKPAAK. The apparent rate of synonymous substitutions in the blocks of RZ is much higher than in the rest of the gene. This can be explained by repeat shuffling within each block. In the C-domain of the orthologous H1 subtype from Medicago truncatula (tribe Trifolieae), a region corresponding to the RZ of Vicieae species was found. It also consists of two blocks of AKPAAK motifs (four and three repeats in the proximal and distal blocks, respectively). These blocks are separated by a 20-amino acid IS. The first 20 amino acids of the Medicago RZ are not part of AKPAAK repeats. We hypothesise that the RZ has most probably evolved as a result of an expansion of AKPAAK repeats from two separate sites in the C-domain. This process started tens of millions of years ago and was most likely directed by positive selection.

Perchloric acid extractable low-Mralbumins SCA and SAA from cotyledons and seed axes of pea (Pisum sativum L.)

Abstract Using 5% HClO4 extraction and 0.9 N acetic acid/8 M urea/15% polyacrylamide gel electrophoresis two new low -M r albumins were revealed in pea (Pisum sativum L) seeds. One of them, termed SCA, predominates among perchloric acid extractable proteins of cotyledons, the other, SAA, in seed axes. Both proteins exhibit similarities in M r (∼10 kDa), amino acid composition, and antigenic properties. Screening of a world-wide pea collection (∼ 900 accessions) revealed three electrophoretic variants of SCA, which demonstrate a monogenic mode of inheritance. The corresponding gene SCA proved to be linked to r-tl gene complex. All but a few cultivated peas have the same SCA variant. No variants of SAA were observed. Three more perchloric extractable proteins reacting with anti-SCA serum in pea seeds were found. Genes of two of them turned out to be linked to SCA. Proteins resembling SCA and SAA by electrophoretic mobility, antigenic properties, and different concentration in cotyledons and seed axes were found in several other legume species examined. A differential expression of SCA and SAA proteins in seed organs might indicate their function to be related to differences in the physiological state of tissues of a germinating seed. There is apparently a family of several SCA-like proteins that are encoded by a cluster of closely linked genes.

Trisomics of garden pea ( Pisum sativum L.) readily respond to selection for increased fertility

428 Earlier, Berdnikov et al. [1] suggested a hypothesis of the origin of plant B-chromosomes from tertiary trisomics. Tertiary trisomics are organisms with the karyotype supplemented with an exchange chromosome formed from fragments of two chromosomes of the normal set via reciprocal translocation. If the exchange chromosome is small, trisomics may arise in the progeny of heterozygotes for translocation owing to abnormal segregation of a tetravalent in meiosis I. Extraploidy brings about gene imbalance, so, trisomics have a lowered vigor and fertility. However, if the region of the main chromosome set covered by the exchange extrachromosome carries a lethal in a homozygous state, while the extrachromosome carries the normal allele, then only extraploid progeny (trisomics) will be viable. This may happen in a small natural population. Under these conditions, natural selection would favor functional diploidization of trisomics, i.e., accumulation of missense mutations in dose-dependent genes, including those in the extrachromosome. With time, the extrachromosome may become “genetically empty,” no longer causing gene imbalance even if present in several doses, and also acquire mechanisms of meiotic drive (preferential transfer to gametes), thereby becoming a B-chromosome.