Pollen dispersal was characterized within a population of the narrowly endemic perennial herb, Centaurea corymbosa, using exclusion-based and likelihood-based paternity analyses carried out on microsatellite data. Data were used to fit a model of pollen dispersal and to estimate the rates of pollen flow and mutation/genotyping error, by developing a new method. Selfing was rare (1.6%). Pollen dispersed isotropically around each flowering plant following a leptokurtic distribution, with 50% of mating pairs separated by less than 11 m, but 22% by more than 40 m. Estimates of pollen flow lacked precision (0-25%), partially because mutations and/or genotyping errors (0.03-1%) could also explain the occurrence of offspring without a compatible candidate father. However, the pollen pool that fertilized these offspring was little differentiated from the adults of the population whereas strongly differentiated from the other populations, suggesting that pollen flow rate among populations was low. Our results suggest that pollen dispersal is too extended to allow differentiation by local adaptation within a population. However, among populations, gene flow might be low enough for such processes to occur.

Using synchronized tobacco Bright Yellow-2 cells and cDNAamplified fragment length polymorphism-based genomewide expression analysis, we built a comprehensive collection of plant cell cycle-modulated genes. Approximately 1,340 periodically expressed genes were identified, including known cell cycle control genes as well as numerous unique candidate regulatory genes. A number of plant-specific genes were found to be cell cycle modulated. Other transcript tags were derived from unknown plant genes showing homology to cell cycle-regulatory genes of other organisms. Many of the genes encode novel or uncharacterized proteins, indicating that several processes underlying cell division are still largely unknown.

SummaryGenetical metabolomics [metabolite profiling combined with quantitative trait locus (QTL) analysis] has been proposed as a new tool to identify loci that control metabolite abundances. This concept was evaluated in a case study with the model tree Populus. Using HPLC, the peak abundances were analyzed of 15 closely related flavonoids present in apical tissues of two full-sib poplar families, Populus deltoides cv. S9-2 · P. nigra cv. Ghoy and P. deltoides cv. S9-2 · P. trichocarpa cv. V24, and correlation and QTL analysis were used to detect flux control points in flavonoid biosynthesis. Four robust metabolite quantitative trait loci (mQTL), associated with rate-limiting steps in flavonoid biosynthesis, were mapped. Each mQTL was involved in the flux control to one or two flavonoids. Based on the identities of the affected metabolites and the flavonoid pathway structure, a tentative function was assigned to three of these mQTL, and the corresponding candidate genes were mapped. The data indicate that the combination of metabolite profiling with QTL analysis is a valuable tool to identify control points in a complex metabolic pathway of closely related compounds.

No abstract

The AFLP technique was used to assess the genetic relationships among the cultivated papaya ( Carica papaya L.) and related species native to Ecuador. Genetic distances based on AFLP data were estimated for 95 accessions belonging to three genera including C. papaya, at least eight Vasconcella species and two Jacaratia species. Cluster analysis using different methods and principal co-ordinate analysis (PCO), based on the AFLP data from 496 polymorphic bands generated with five primer combinations, was performed. The resulted grouping of accessions of each species corresponds largely with their taxonomic classifications and were found to be consistent with other studies based on RAPD, isozyme and cpDNA data. The AFLP analysis supports the recent rehabilitation of the Vasconcella group as a genus; until recently Vasconcella was considered as a section within the genus Carica. Both cluster and PCO analysis clearly separated the species of the three genera and illustrated the large genetic distance between C. papaya accessions and the Vasconcella group. The specific clustering of the highly diverse group of Vasconcella x heilbornii accessions also suggests that these genotypes may be the result of bi-directional introgression events between Vasconcella stipulata and Vasconcella cundinamarcensis.

Aim The downstream hydrochoric spread of seeds of aquatic and riparian plant species, without upstream compensation, can be expected to result in downstream accumulation of population genetic diversity. This idea has been termed the 'unidirectional dispersal hypothesis' and is the genetic equivalent of the more generally known 'drift paradox'. Our aim was to test this unidirectional diversity hypothesis, and to present a general synthesis of the patterns of population genetic variation across different riparian and aquatic plant species along rivers.Location The Meuse River (Belgium) and rivers world-wide.Methods First, we used amplified fragment length polymorphism markers to compare patterns of within-and between-population genetic diversity among three riparian plant species (Sisymbrium austriacum, Erysimum cheiranthoides and Rorippa sylvestris), typically occurring in different habitats along a gradient perpendicular to the Meuse River. Second, we performed a meta-analysis on studies reporting on the population genetic structure of riparian and aquatic plant species along rivers.Results Along the Meuse River, we found significant genetic differentiation among populations of all three riparian species, and significant isolation by distance for one of them (R. sylvestris). There was no clear association between the typical habitat of a species and its population genetic structure. None of the three species provided evidence for the unidirectional dispersal hypothesis. The meta-analysis, based on 21 data records, did not support the unidirectional dispersal hypothesis either. Average weighted population genetic differentiation across species was significant.Main conclusions Important mechanisms of upstream seed dispersal, probably through zoochory, together with higher seed recruitment opportunities in upstream habitats due to density dependence of recruitment, may explain the absence of downstream accumulation of genetic diversity. Also, it seems difficult to find consistent patterns in genetic variation in species from aquatic and riparian habitats. We argue that this is due to the recurrent extinctions and colonizations characteristic of these habitats, resulting in complex genetic patterns. Our results strongly support previous suggestions that stream ecology should consistently embrace metapopulation theory to be able to understand patterns of genetic diversity, as well as species diversity.

Using a low-salt extractlon procedure, we isolated nuclear scaffolds from tobacco that bind specific plant DNA fragments in vitro. One of these fragments was characterized in more detail; this characterization showed that it contains sequences with structural propertles analogous to animal scaffold attachment regions (SARs). We showed that scaffold attachment is evolutlonarily conserved between plants and animals, although different SARs have different binding affinities. Furthermore, we demonstrated that flanking a chimeric transgene with the characterized SAR-containing fragment reduces significantly the varlation in expression in series of transformants with an active insertlon, whereas a SAR fragment from the human P-globin locus does not. Moreover, the frequency distribution patterns of transgene activities showed that most of the transformants containing the plant SAR fragment had expression levels clustered around the mean. These data suggest that the particular plant DNA fragment can insulate the reporter gene from expression-influencing effects exerted from the host chromatin.

An improved cDNA-AFLP method for genomewide expression analysis has been developed. We demonstrate that this method is an efficient tool for quantitative transcript profiling and a valid alternative to microarrays. Unique transcript tags, generated from reverse-transcribed messenger RNA by restriction enzymes, were screened through a series of selective PCR amplifications. Based on in silico analysis, an enzyme combination was chosen that ensures that at least 60% of all the mRNAs were represented by an informative sequence tag. The sensitivity and specificity of the method allows one to detect poorly expressed genes and distinguish between homologous sequences. Accurate gene expression profiles were determined by quantitative analysis of band intensities, and subtle differences in transcriptional activity were revealed. A detailed screen for cell cycle-modulated genes in tobacco demonstrates the usefulness of the technology for genome-wide expression analysis.