Genetic studies on the acidification capacity of sunflower roots induced under iron stress

Under stress of iron deficiency roots of sunflower (Helianthus annuus L.) increase proton efflux which acidifies the root medium, increase the ferric reducing capacity and the exudation of phenolic compounds. Differences have been found previously among sunflower inbred lines in the capacity of their roots to lower pH and it was also found that this character is under genetic control.This work presents the results of an inheritance study made by crossing two genotypes, one (CMS HA 89) without acidification capacity and another (RHA 271) with it. Plants were grown individually in 75 mL vessels with an aerated solution low in iron. After 4 days, solutions were changed to one without iron and the pH of the medium was measured during the following days. Results from F₁, F₂, and backcross generations can be explained with two pairs of alleles controlling the character, being the relation between alleles of complete dominance at both gene pairs, but either gene, when dominant is epistatic to the other.     

Genetic structure of the population of Sicily.

Genetic heterogeneity within Sicily was investigated on the basis of ACP1, ADA, ESD, GLO1, PGD, PGM1, PGM2, SODA, ABO, and MN gene frequencies, and compared to those of other regions of Italy for which these same loci have been examined. Correspondence analysis revealed no differences within the island, at least at the provincial level, but showed genetic differentiation among Italian regions, distinctly clustering northern, central, and southern populations, respectively. These data indicate a close relationship between Sicily and southern Italy. In addition, the contribution of Middle Eastern populations to the gene pool of Sicily was evident.     

Chymotrypsin-like enzymes are involved in sperm penetration through the vitelline coat of Ciona intestinalis egg

In Ciona intestinalis, sperm penetration through the egg vitelline coat is an essential event of fertilization. We investigated whether trypsin- and chymotrypsin-like enzymes are involved in this event. Inhibitors and peptide substrates for chymotrypsin-like enzymes blocked the overall process of fertilization in a concentration-dependent manner. The inhibitory activity was specifically exerted on the step of sperm penetration. Chymotrypsin-like protease activity was identified in spermatozoa with the fluorogenic synthetic substrate Suc-Ala-Ala-Phe-AMC, which was the most effective substrate in blocking sperm penetration. These data indicate that a chymotrypsin-like protease activity is a sperm lysin of Ciona intestinalis.     

Variation in nitrate metabolism in biovars of Pseudomonas solanacearum

A collection of 327 strains of Pseudomonas solanacearum , representing five biovars, was divisible into three groups on the basis of differences in nitrate metabolism. Nine strains (2.8%), of which seven were biovar 2 from bacterial wilt of potato, were nitrate reduction-deficient and failed to produce nitrite from nitrate by either of two methods of detection in five different media. A second group of 231 strains, comprising biovars 1 and 2 and a single biovar 3 strain, produced nitrite from nitrate and grew vigorously in the presence of nitrate under anaerobic conditions but were deficient in ability to denitrify. A third group comprising 57 strains of biovar 3, 28 of biovar 4 and one each of biovar 2 and 5 produced nitrite from nitrate and gave profuse growth and gas production from nitrate under anaerobic conditions. However, production of gas from nitrate (denitrification) was not a consistently reproducible property in some of the media tested. Gas production results were most reproducible when a semi-solid succinate/nitrate or glycerol/nitrate medium was used. Serial passage of four nitrate reduction-deficient isolates in nitrate medium did not restore ability to reduce nitrate.     

Processing of the intron-encoded U16 and U18 snoRNAs: the conserved C and D boxes control both the processing reaction and the stability of the mature snoRNA.

A novel class of small nucleolar RNAs (snoRNAs), encoded in introns of protein coding genes and originating from processing of their precursor molecules, has recently been described. The L1 ribosomal protein (r-protein) gene of Xenopus laevis and its human homologue contain two snoRNAs, U16 and U18. It has been shown that these snoRNAs are excised from their intron precursors by endonucleolytic cleavage and that their processing is alternative to splicing. Two sequences, internal to the snoRNA coding region, have been identified as indispensable for processing the conserved boxes C and D. Competition experiments have shown that these sequences interact with diffusible factors which can bind both the pre-mRNA and the mature U16 snoRNA. Fibrillarin, which is known to associate with complexes formed on C and D boxes of other snoRNAs, is found in association with mature U16 RNA, as well as with its precursor molecules. This fact suggests that the complex formed on the pre-mRNA remains bound to U16 throughout all the processing steps. We also show that the complex formed on the C and D boxes is necessary to stabilize mature snoRNA.     

Loss of the ORF in the SSUrDNA group I intron of one Naegleria lineage.

We have found a Naegleria lineage in which the SSUrDNA contains a group I intron with a length of 375 nucleotides. This is a unique finding because all group I introns detected until now in Naegleria are 1.3 kilobases long and contain an open reading frame coding for 245 amino acids. Sequence data show that the 375 nucleotide-long intron is at the same place in the SSUrDNA as, and is descendant from, the 1.3 kilobase group I intron present in other species of Naegleria. Our data indicate that in one lineage of Naegleria the group I intron lost part of its DNA that is not contributing to the secondary structure but that carries the open reading frame. The amoeboflagellate genus Naegleria contains strains without the intron and strains with the intron, with or without an open reading frame. Therefore, this genus provides a unique opportunity to study the function and evolution of both the group I intron and the open reading frame.