Dated molecular phylogenies are the basis for understanding species diversity and for linking changes in rates of diversification with historical events such as restructuring in developmental pathways, genome doubling, or dispersal onto a new continent. Valid fossil calibration points are essential to the accurate estimation of divergence dates, but for many groups of flowering plants fossil evidence is unavailable or limited. Arabidopsis thaliana, the primary genetic model in plant biology and the first plant to have its entire genome sequenced, belongs to one such group, the plant family Brassicaceae. Thus, the timing of A. thaliana evolution and the history of its genome have been controversial. We bring previously overlooked fossil evidence to bear on these questions and find the split between A. thaliana and Arabidopsis lyrata occurred about 13 Mya, and that the split between Arabidopsis and the Brassica complex (broccoli, cabbage, canola) occurred about 43 Mya. These estimates, which are two-to threefold older than previous estimates, indicate that gene, genomic, and developmental evolution occurred much more slowly than previously hypothesized and that Arabidopsis evolved during a period of warming rather than of cooling. We detected a 2-to 10-fold shift in species diversification rates on the branch uniting Brassicaceae with its sister families. The timing of this shift suggests a possible impact of the Cretaceous-Paleogene mass extinction on their radiation and that Brassicales codiversified with pierid butterflies that specialize on mustard-oil-producing plants.he most important genetic model in plant biology is Arabidopsis thaliana. It is the first plant to have its entire genome sequenced, and it serves as a key comparison point with other eukaryotic genomes. A. thaliana is diploid and has a small genome distributed on just five chromosomes, considerations in its choice as a model (1). The age of the Arabidopsis crown group (CG), previously estimated at 5.8-3 Mya (2, 3), and of splits within Brassicaceae have been used to understand the pace of evolution in genes affecting self-incompatibility (4, 5), the rate of change in signal transduction and gene expression (6, 7), the persistence of shared chromosomal rearrangements in A. thaliana and Brassica oleracea (8), the tempo of evolution of miRNA sequences (9), the evolution of pierid butterflies specializing in plants that produce mustard oils (10), and the ages of wholegenome duplication (WGD) events giving rise to gene pairs in Arabidopsis (11). As genomes of additional Brassicaceae (e.g., Capsella rubella) and other Brassicales (e.g., Carica papaya) (12) are sequenced, the importance of robust estimates of divergence dates relating these genomes to one another and to the geological record increases substantially.The accuracy of divergence times inferred from sequence data depends on valid, verifiable fossils to calibrate phylogenetic trees. Previous dates for the origin of Arabidopsis relied on the report of fossil pollen assigned to the genus Rori...

Recent epidemiological studies have established an association between the common consumption of coffee or other caffeinated beverages and a reduced risk of developing Parkinson's disease (PD). To explore the possibility that caffeine helps prevent the dopaminergic deficits characteristic of PD, we investigated the effects of caffeine and the adenosine receptor subtypes through which it may act in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin model of PD. Caffeine, at doses comparable to those of typical human exposure, attenuated MPTP-induced loss of striatal dopamine and dopamine transporter binding sites. The effects of caffeine were mimicked by several A(2A) antagonists (7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH 58261), 3,7-dimethyl-1-propargylxanthine, and (E)-1,3-diethyl-8 (KW-6002)-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione) (KW-6002) and by genetic inactivation of the A(2A) receptor, but not by A(1) receptor blockade with 8-cyclopentyl-1,3-dipropylxanthine, suggesting that caffeine attenuates MPTP toxicity by A(2A) receptor blockade. These data establish a potential neural basis for the inverse association of caffeine with the development of PD, and they enhance the potential of A(2A) antagonists as a novel treatment for this neurodegenerative disease.

Abstract. A critical review of characters used in the systematics of the Brassicaceae is given, and aspects of the origin, classification, and generic delimitation of the family discussed. Molecular phylogenetic studies of the family were reviewed, and major clades identified. Based on molecular studies, especially from the ndhF chloroplast gene, and careful evaluation of morphology and generic circumscriptions, a new tribal alignment of the Brassicaceae is proposed. In all, 25 tribes are recognized, of which seven (Aethionemeae, Boechereae, Descurainieae, Eutremeae, Halimolobeae, Noccaeeae, and Smelowskieae) are described as new. For each tribe, the center(s) of distribution, morphology, and number of taxa are given. Of the 338 genera currently recognized in the Brassicaceae, about 260 genera (or about 77%) were either assigned or tentatively assigned to the 25 tribes. Some problems relating to various genera and tribes are discussed, and future research developments are briefly covered.

To estimate the evolutionary history of the mustard family (Brassicaceae or Cruciferae), we sampled 113 species, representing 101 of the roughly 350 genera and 17 of the 19 tribes of the family, for the chloroplast gene ndhF. The included accessions increase the number of genera sampled over previous phylogenetic studies by four-fold. Using parsimony, likelihood, and Bayesian methods, we reconstructed the phylogeny of the gene and used the Shimodaira-Hasegawa test (S-H test) to compare the phylogenetic results with the most recent tribal classification for the family. The resultant phylogeny allowed a critical assessment of variations in fruit morphology and seed anatomy, upon which the current classification is based. We also used the S-H test to examine the utility of trichome branching patterns for describing monophyletic groups in the ndhF phylogeny. Our phylogenetic results indicate that 97 of 114 ingroup accessions fall into one of 21 strongly supported clades. Some of these clades can themselves be grouped into strongly to moderately supported monophyletic groups. One of these lineages is a novel grouping overlooked in previous phylogenetic studies. Results comparing 30 different scenarios of evolution by the S-H test indicate that five of 12 tribes represented by two or more genera in the study are clearly polyphyletic, although a few tribes are not sampled well enough to establish para- or polyphyly. In addition, branched trichomes likely evolved independently several times in the Brassicaceae, although malpighiaceous and stellate trichomes may each have a single origin.

Highlights d m 6 A sites are highly maintained at different Arabidopsis developmental stages d Many m 6 A sites stabilize Arabidopsis adult leaf transcripts d m 6 A stabilizes mRNAs through inhibition of local ribonucleolytic cleavage d Dynamic, stress-specific m 6 A sites stabilize stress response protein transcripts