Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper

Tomato and pepper are two Solanaceous fruit crops that display an enormous diversity in fruit morphology. In this review, we will present an overview of the history of tomato and pepper and discuss key plant traits that were specifically selected during domestication of the two species. The traits discussed are fruit weight, shape, colour, ripening, pungency and plant architecture. We will review these characteristics as well as the genetic loci or genes that control these features, questioning whether mutations at orthologous loci occurred independently in these two species or whether unique plant and fruit features resulted in selection at different genes.     

Effect of salinity changes on the bacterial diversity, photosynthesis and oxygen consumption of cyanobacterial mats from an intertidal flat of the Arabian Gulf

The effects of salinity fluctuation on bacterial diversity, rates of gross photosynthesis (GP) and oxygen consumption in the light (OCL) and in the dark (OCD) were investigated in three submerged cyanobacterial mats from a transect on an intertidal flat. The transect ran 1 km inland from the low water mark along an increasingly extreme habitat with respect to salinity. The response of GP, OCL and OCD in each sample to various salinities (65 per thousand, 100 per thousand, 150 per thousand and 200 per thousand) were compared. The obtained sequences and the number of unique operational taxonomic units showed clear differences in the mats' bacterial composition. While cyanobacteria decreased from the lower to the upper tidal mat, other bacterial groups such as Chloroflexus and Cytophaga/Flavobacteria/Bacteriodetes showed an opposite pattern with the highest dominance in the middle and upper tidal mats respectively. Gross photosynthesis and OCL at the ambient salinities of the mats decreased from the lower to the upper tidal zone. All mats, regardless of their tidal location, exhibited a decrease in areal GP, OCL and OCD rates at salinities > 100 per thousand. The extent of inhibition of these processes at higher salinities suggests an increase in salt adaptation of the mats microorganisms with distance from the low water line. We conclude that the resilience of microbial mats towards different salinity regimes on intertidal flats is accompanied by adjustment of the diversity and function of their microbial communities.     

The tomato homolog of the gene encoding UV-damaged DNA binding protein 1 (DDB1) underlined as the gene that causes the<Emphasis Type="Italic"> high pigment-1</Emphasis> mutant phenotype

A tomato EST sequence, highly homologous to the human and Arabidopsis thaliana UV-damaged DNA binding protein 1 (DDB1), was mapped to the centromeric region of the tomato chromosome 2. This region was previously shown to harbor the HP-1 gene, encoding the high pigment-1 (hp-1) and the high pigment-1^w (hp-1^w) mutant phenotypes. Recent results also show that the A. thaliana DDB1 protein interacts both genetically and biochemically with the protein encoded by DEETIOLATED1, a gene carrying three tomato mutations that are in many respects isophenotypic to hp-1: high pigment-2 (hp-2), high pigment-2^j (hp-2^j) and dark green (dg). The entire coding region of the DDB1 gene was sequenced in an hp-1 mutant and its near-isogenic normal plant in the cv. Ailsa Craig background, and also in an hp-1^w mutant and its isogenic normal plant in the GT breeding line background. Sequence analysis revealed a single A⁹³¹-to-T⁹³¹ base transversion in the coding sequence of the DDB1 gene in the hp-1 mutant plants. This transversion results in the substitution of the conserved asparagine at position 311 to a tyrosine residue. In the hp-1^w mutant, on the other hand, a single G²³⁹²-to-A²³⁹² transition was observed, resulting in the substitution of the conserved glutamic acid at position 798 to a lysine residue. The single nucleotide polymorphism that differentiates hp-1 mutant and normal plants in the cv. Ailsa Craig background was used to design a pyrosequencing genotyping system. Analysis of a resource F₂ population segregating for the hp-1 mutation revealed a very strong linkage association between the DDB1 locus and the photomorphogenic response of the seedlings, measured as hypocotyl length (25<LOD score<26, R²=62.8%). These results strongly support the hypothesis that DDB1 is the gene encoding the hp-1 and hp-1^w mutant phenotypes.Communicated by R. Hagemann     

In situ substrate conversion and assimilation by nitrifying bacteria in a model biofilm

Local nitrification and carbon assimilation activities were studied in situ in a model biofilm to investigate carbon yields and contribution of distinct populations to these activities. Immobilized microcolonies (related to Nitrosomonas europaea/eutropha, Nitrosomonas oligotropha, Nitrospira sp., and to other Bacteria) were incubated with [14C]-bicarbonate under different experimental conditions. Nitrifying activity was measured concomitantly with microsensors (oxygen, ammonium, nitrite, nitrate). Biofilm thin sections were subjected to fluorescence in situ hybridization (FISH), microautoradiography (MAR), and local quantification of [14C]-bicarbonate uptake (beta microimaging). Nitrifying activity and tracer assimilation were restricted to a surface layer of different thickness in the various experiments (substrate or oxygen limitation). Excess oxygen uptake under all conditions revealed heterotrophic activity fuelled by decay or excretion products during active nitrification. Depth limits and intensity of tracer incorporation profiles were in agreement with ammonia-oxidation activity (measured with microsensors), and distribution of incorporated tracer (detected with MAR). Microautoradiography revealed a sharp individual response of distinct populations in terms of in-/activity depending on the (local) environmental conditions within the biofilm. Net in situ carbon yields on N, expressed as e- equivalent ratios, varied between 0.005 and 0.018, and, thus, were in the lower range of data reported for pure cultures of nitrifiers.     

KCNK?: opening and closing the 2-P-domain potassium leak channel entails "C-type" gating of the outer pore.

Essential to nerve and muscle function, little is known about how potassium leak channels operate. KCNK? opens and closes in a kinase-dependent fashion. Here, the transition is shown to correspond to changes in the outer aspect of the ion conduction pore. Voltage-gated potassium (VGK) channels open and close via an internal gate; however, they also have an outer pore gate that produces "C-type" inactivation. While KCNK? does not inactivate, KCNK? and VGK channels respond in like manner to outer pore blockers, potassium, mutations, and chemical modifiers. Structural relatedness is confirmed: VGK residues that come close during C-type gating predict KCNK? sites that crosslink (after mutation to cysteine) to yield channels controlled by reduction and oxidization. We conclude that similar outer pore gates mediate KCNK? opening and closing and VGK channel C-type inactivation despite their divergent structures and physiological roles.     

Chemical Detection of Microbial Prey by Bacterial Predators

A motile, predacious bacterium which degraded Pythium debaryanum was strongly attracted to substances released into the medium by the fungus. A nonpredacious bacterium was not attracted to these substances. The predator bacterium was specifically attracted to cellulose and its oligomers which are known to be components of the cell wall of Pythium. Ethanol inhibited chemotaxis of the bacterium without affecting either its motility or its ability to degrade cellulose. A second predacious bacterium was isolated for the alga, Skeletonema costatum. The role of chemoreception in the detection of microbial prey by bacterial predators in natural habitats is discussed.     

Selective toxicity of engineered lentivirus lytic peptides in a CF airway cell model

Lentivirus lytic peptides (LLPs) are derived from HIV-1 and have antibacterial properties. LLP derivatives (eLLPs) were engineered for greater potency against Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA). Minimum bactericidal concentration (MBC) was determined in low and physiologic salt concentrations. MBC was decreased against SA and equivalent against PA in physiologic salt when compared to the parent compound LLP1. In a novel cystic fibrosis (CF) airway cell model, one derivative, WLSA5, reduced the number of adherent PA and only moderately affected CF cell viability. Overall, eLLPs are selectively toxic to bacteria and may be useful against CF airway infections.