BackgroundEpigenetic modifications, such as cytosine methylation, are inherited in plant species and may occur in response to biotic or abiotic stress, affecting gene expression without changing genome sequence. Laguncularia racemosa, a mangrove species, occurs in naturally contrasting habitats where it is subjected daily to salinity and nutrient variations leading to morphological differences. This work aims at unraveling how CpG-methylation variation is distributed among individuals from two nearby habitats, at a riverside (RS) or near a salt marsh (SM), with different environmental pressures and how this variation is correlated with the observed morphological variation.Principal FindingsSignificant differences were observed in morphological traits such as tree height, tree diameter, leaf width and leaf area between plants from RS and SM locations, resulting in smaller plants and smaller leaf size in SM plants. Methyl-Sensitive Amplified Polymorphism (MSAP) was used to assess genetic and epigenetic (CpG-methylation) variation in L. racemosa genomes from these populations. SM plants were hypomethylated (14.6% of loci had methylated samples) in comparison to RS (32.1% of loci had methylated samples). Within-population diversity was significantly greater for epigenetic than genetic data in both locations, but SM also had less epigenetic diversity than RS. Frequency-based (GST) and multivariate (βST) methods that estimate population structure showed significantly greater differentiation among locations for epigenetic than genetic data. Co-Inertia analysis, exploring jointly the genetic and epigenetic data, showed that individuals with similar genetic profiles presented divergent epigenetic profiles that were characteristic of the population in a particular environment, suggesting that CpG-methylation changes may be associated with environmental heterogeneity.ConclusionsIn spite of significant morphological dissimilarities, individuals of L. racemosa from salt marsh and riverside presented little genetic but abundant DNA methylation differentiation, suggesting that epigenetic variation in natural plant populations has an important role in helping individuals to cope with different environments.

Forest fragments along the Atlantic coastland of Brazil have been highly impacted by extensive human activities for the last 400 years. Caesalpinia echinata (Leguminosae-Caesalpinioideae), brazilwood, was overexploited during this period due to its economical importance as a dye. As a result, the species has become endangered and today its total population size is very restricted. We have assessed the distribution of genetic variation between five natural populations of brazilwood by means of RAPD (random amplified polymorphic DNA) markers. Of the total genetic variability, 28.5% was attributable to differences between two geographical groups, 29.6% to population differences within groups and 42.0% to individual differences within populations. The high level of population differentiation observed is in contrast to that expected for a primarily outcrossed woody perennial plant, and suggests that there may be a degree of inbreeding. Our results are in agreement with previous studies which postulated that C. echinata has always occurred in clumps, being common in some places but rare in between. From a conservation point of view, different populations representing different regions should be protected and, yet, plants with different origins should not be synthesized into populations in a recovery process at the risk of loss and dilution of genetic information. This study demonstrates that RAPD markers were effective in establishing a clear correlation between genetic and geographical distance and in identifying areas of maximum diversity, and may be used as an initial approach to assess the partitioning of genetic variation in this endangered species.Peer reviewe

Heart-of-palm (Euterpe edulis Mart.) is a wild palm with a wide distribution throughout the Atlantic Rainforest. Populations of E. edulis represent important renewable natural resources but are currently under threat from predatory exploitation. Furthermore, because the species is indigenous to the Atlantic Rainforest, which is located in the most economically developed and populated region of Brazil, social and economic pressures have devastated heart-of-palm forests. In order to estimate the partitioning of genetic variation of endangered E. edulis populations, 429 AFLP markers were used to analyse 150 plants representing 11 populations of the species distribution range. Analysis of the genetic structure of populations carried out using analysis of molecular variance (AMOVA) revealed moderate genetic variation within populations (57. 4%). Genetic differentiation between populations (FST = 0.426) was positively correlated with geographical distance. These results could be explained by the historical fragmentation of the Atlantic coastal region, together with the life cycle and mating system. The data obtained in this work should have important implications for conservation and future breeding programmes of E. edulis.