Arabidopsis thaliana is one of the most intensively studied plant species. More recently, information is accumulating about its closest relatives, the former genus CARDAMINOPSIS: A. thaliana diverged from these relatives, actually treated within three major lineages (Arabidopsis lyrata, Arabidopsis halleri, and Arabidopsis arenosa), [almost equal to]5 mya. Significant karyotype evolution in A. thaliana with base chromosome number reduction from x=8 to x=5 might indicate and favor effective genetic isolation from these other species, although hybrids are occurring naturally and have been also constituted under controlled conditions. We tested the evolutionary significance to separate the x=5 from the x=8 lineage using DNA sequence data from the plastome and the nuclear ribosomal DNA based on an extensive, representative worldwide sampling of nearly all taxonomic entities. We conclude that (i) A. thaliana is clearly separated phylogenetically from the x=8 lineage, (ii) five major lineages outside A. thaliana can be identified (A. lyrata, A. arenosa, A. halleri, Arabidopsis croatica, and Arabidopsis pedemontana) together with Arabidopsis cebennensis, and (iii) centers of genetic and morphological diversity are mostly in congruence and are located close to the Balkans in Austria and Slovakia outside glaciated and permafrost regions with few notable exceptions.

A potential mechanism of light regulation of the succinate dehydrogenase (SDH) expression in Arabidopsis thaliana leaves was studied. As was shown by dot-hybridization and polymerase chain reaction in real time (RT-PCR), the SDH mRNA level in wild-type Arabidopsis thaliana plants changed depending on light conditions. The level of SDH mRNA in darkness was higher than in the light. The analysis of Arabidopsis thaliana plants carrying the mutant genes of phytochromes A and B showed that phytochrome A was involved in the regulation of the SDH enzyme activity. The active form of phytochrome A suppressed the SDHI-2 gene expression, and that resulted in decreasing activity of SDH.

The information on morphological and anatomical features of Arabidopsis thaliana (L.) Нeynh. root mutants cultured in vivo and searching of an optimal conditions for plants growth is presented. The positive effect of presence into substrate of diatoms (Bacillariophyta) on A. thaliana plants growth and development is recorded. | Наведено дані щодо морфолого-анатомічних ознак кореневих мутантів рослин Arabidopsis thaliana (L.) Heynh. під час його культивування in vivo з метою підбору оптимальних умов вирощування рослин. Відмічено позитивний вплив на рост і розвиток рослин A. thaliana наявності у субстраті діатомових водоростей (Bacillariophyta).

Seeds of Arabidopsis thaliana are hosts for three mycotoxin-producing Aspergillus species, A. flavus, A. nidulans and A. parasiticus, enabling an Aspergillus-Arabidopsis infection (AAI) assay to be developed. The AAI assay involved inoculation of 10- to 12-mg aliquots of uniformly cultivated, surface-sterilized A. thaliana seeds in microcentrifuge tubes. Use of microcentrifuge tubes facilitated qualitative and quantitative analyses of post-infection characteristics such as sporulation and mycotoxin production. Cultivation of A. thaliana seeds under uniform environmental conditions is necessary to limit genotype-independent seed-lot variability. Using the A. nidulans oxylipin mutant, ΔppoABC, and two well-characterized A. thaliana pathogen-defence mutants, ein2-1 and pad4-1, the AAI assay permitted genetic analysis of seed infection and mycotoxin production. Sporulation, but not mycotoxin production, was impaired in A. nidulans ΔppoABC, while A. thaliana ein2-1 and pad4-1 had a small but detectable influence on A. nidulans sporulation that appeared to be dependent on seed age.

Cytosine methylation of repetitive sequences is widespread in plant genomes, occurring in both symmetric (CpG and CpNpG) as well as asymmetric sequence contexts. We used the methylation-dependent restriction enzyme McrBC to profile methylated DNA using tiling microarrays of Arabidopsis Chromosome 4 in two distinct ecotypes, Columbia and Landsberg erecta. We also used comparative genome hybridization to profile copy number polymorphisms. Repeated sequences and transposable elements (TEs), especially long terminal repeat retrotransposons, are densely methylated, but one third of genes also have low but detectable methylation in their transcribed regions. While TEs are almost always methylated, genic methylation is highly polymorphic, with half of all methylated genes being methylated in only one of the two ecotypes. A survey of loci in 96 Arabidopsis accessions revealed a similar degree of methylation polymorphism. Within-gene methylation is heritable, but is lost at a high frequency in segregating F(2) families. Promoter methylation is rare, and gene expression is not generally affected by differences in DNA methylation. Small interfering RNA are preferentially associated with methylated TEs, but not with methylated genes, indicating that most genic methylation is not guided by small interfering RNA. This may account for the instability of gene methylation, if occasional failure of maintenance methylation cannot be restored by other means.

cyclo-Oxylipin-galactolipids (cGL) are mono- or digalactosyldiglycerides carrying a cyclo-oxylipin in the sn1- and/or sn2-position or esterified to the galactose moiety. These compounds were recently identified in Arabidopsis thaliana. We provide evidence that cGL are mainly, if not exclusively, part of the thylakoid and can be hydrolysed by lipolytic activities associated with photosynthesis-related protein complexes in vitro. Using HPLC/ESI-mass spectrometry, cGL are shown to be restricted in occurrence to the genus Arabidopsis, they do not occur in other plants tested. A. thaliana cGL are rapidly and transiently formed upon wounding with characteristic changes in composition of the cGL-fraction. While the biological role of cGL is not understood, the genus Arabidopsis may present a model-case of chemical evolution of a novel class of regulatory molecules.

Canalization is a fundamental feature of many developmental systems, yet the genetic basis for this property remains elusive. We examine the genetic basis of microenvironmental canalization in the model plant Arabidopsis thaliana, focusing on differential developmental stability between genotypes in one fitness and four quantitative morphological traits. We measured developmental stability in genetically identical replicates of two populations of recombinant inbred (RI) lines and one population of geographically widespread accessions of A. thaliana grown in two different photoperiod-controlled environments. We were able to map quantitative trait loci associated with developmental stability. We also identified a candidate gene, ERECTA, that may contribute to microenvironmental canalization in rosette leaf number under long-day photoperiods, and analysis of mutant lines indicates that the er-105 allele results in increased canalization for this trait. ERECTA, which encodes a signaling protein, appears to act as an ecological amplifier by transducing developmental noise (e.g., microenvironmental variation) into phenotypic differentiation. We also measured genotypic selection on four plant architecture traits and find evidence for selection for both increased and decreased canalization at various traits.