Reduction of bacterial genome size and expansion resulting from obligate intracellular lifestyle and adaptation to soil habitat.

Prokaryotic organisms are exposed in the course of evolution to various impacts, resulting often in drastic changes of their genome size. Depending on circumstances, the same lineage may diverge into species having substantially reduced genomes, or such whose genomes have undergone considerable enlargement. Genome reduction is a consequence of obligate intracellular lifestyle rendering numerous genes expendable. Another consequence of intracellular lifestyle is reduction of effective population size and limited possibility of gene acquirement via lateral transfer. This causes a state of relaxed selection resulting in accumulation of mildly deleterious mutations that can not be corrected by recombination with the wild type copy. Thus, gene loss is usually irreversible. Additionally, constant environment of the eukaryotic cell renders that some bacterial genes involved in DNA repair are expandable. The loss of these genes is a probable cause of mutational bias resulting in a high A+T content. While causes of genome reduction are rather indisputable, those resulting in genome expansion seem to be less obvious. Presumably, the genome enlargement is an indirect consequence of adaptation to changing environmental conditions and requires the acquisition and integration of numerous genes. It seems that the need for a great number of capabilities is common among soil bacteria irrespective of their phylogenetic relationship. However, this would not be possible if soil bacteria lacked indigenous abilities to exchange and accumulate genetic information. The latter are considerably facilitated when housekeeping genes are physically separated from adaptive loci which are useful only in certain circumstances.</jats:p

Two plant signalling peptides: systemin and ENOD 40.

Recently several new evidences have appeared on biological role of native short peptides. This is an overview on two of them occurring in plants: systemin and ENOD 40.</jats:p

An efficient method of genomic DNA isolation from plant tissues.

The manuscript describes an easy method of isolation of plant genomic DNA. This method allowed us to isolate substantial amounts of good quality DNA from lupin (Lupinus luteus) tissues. The described method also appeared to be useful for genomic DNA isolation from tissues of other plants.</jats:p

Structure of yellow lupine genes coding for mitotic cyclins.

Cell cycle progression in eukaryotes is controlled by complexes of p34 protein kinases and cyclins. For the first time in plants, we have established the sequence of four yellow lupine mitotic cyclin B1 genes. Their coding regions and expression pattern were also characterised recently. Structure of all the four lupine genes is similar: they consist of nine exons and eight introns, analogously located, except Luplu;CycB1;3 lacking 7th intron. Analysis of 5'-regulatory sequences of two of them showed that both comprise M-specific activators (MSA), common to plant genes induced in late G2 and early M. Putative repressor binding sites CDE/CHR found in animal G2-specific promoters can also be detected in lupine genes. Controlling region of Luplu;CycB1;4 gene that is highly activated by IAA, contains up to 7 auxin response elements, while insensible to IAA Luplu;CycB1;4 gene have no such motifs. Further studies should be undertaken to determine precisely the functions of putative regulatory elements in the expression of lupine mitotic cyclins.</jats:p

Isolation and classification of a family of cyclin gene homologues in Lupinus luteus.

The lupine (Lupinus luteus cv. Ventus) cDNA clones encoding homologues of cyclin (CycB1;2, CycB1;3, CycB1;4) have been isolated from cDNA library prepared from roots inoculated with Bradyrhizobium lupini. Comparison of the deduced amino-acid sequences of CycB1;2, CycB1;3, CycB1;4 and previously described CycB1;1 (Deckert et al. 1996, Biochimie 78, 90-94) showed that they share 46-65% of identical amino acids. The presence of conserved residues (Renaudin et. al., in The Plant Cell Cycle, in the press; Renaudin et al., Plant Mol. Biol, in the press) along with phylogenetic analysis of known plant cyclins revealed that the four lupine sequences belong to subgroup 1 of B-like mitotic cyclins.</jats:p

Characterization and expression analysis of the yellow lupin (Lupinus luteus L.) gene coding for nodule specific proline-rich protein.

The LlPRP2 gene coding for a proline-rich protein shows a high level of similarity to, as well as significant differences from the family of ENOD2 nodule-specific genes. Several sequence motifs with putative regulatory function were identified in the 5' and 3' noncoding regions of the LlPRP2 gene. Northern blot analysis revealed that the expression of the LlPRP2 gene begins 9 days after inoculation of yellow lupin roots with Bradyrhizobium sp. (Lupinus); the expression is restricted to symbiotic nodules and is not detected in other tissues or organs. Detailed hybridization analysis showed that, when expression is activated, the LlPRP2 transcript is modified so as to produce at least three bands and a continuous distribution of decay intermediates. The modification of the LlPRP2 transcript probably involves degradation from the 5'- and/or 3'-ends of the RNA molecules. Southern blot analysis indicates that only one gene is present in the yellow lupin genome. The presence of genes homologous to the LlPRP2 gene was confirmed for three cultivars of yellow lupin and for Lupinus angustifolius. However, LlPRP2 homologues were not detected in Lupinus albus cv. Bac, indicating that this plant may lack the ENOD2 sequence.</jats:p