Adventitious rooting in response to long-term cold: a possible mechanism of clonal growth in alpine perennials.

Arctic alpine species experience extended periods of cold and unpredictable conditions during flowering. Thus, often, alpine plants use both sexual and asexual means of reproduction to maximize fitness and ensure reproductive success. We used the arctic alpine perennial Arabis alpina to explore the role of prolonged cold exposure on adventitious rooting. We exposed plants to 4°C for different durations and scored the presence of adventitious roots on the main stem and axillary branches. Our physiological studies demonstrated the presence of adventitious roots after 21 weeks at 4°C saturating the effect of cold on this process. Notably, adventitious roots on the main stem developing in specific internodes allowed us to identify the gene regulatory network involved in the formation of adventitious roots in cold using transcriptomics. These data and histological studies indicated that adventitious roots in A. alpina stems initiate during cold exposure and emerge after plants experience growth promoting conditions. While the initiation of adventitious root was not associated with changes of DR5 auxin response and free endogenous auxin level in the stems, the emergence of the adventitious root primordia was. Using the transcriptomic data, we discerned the sequential hormone responses occurring in various stages of adventitious root formation and identified supplementary pathways putatively involved in adventitious root emergence, such as glucosinolate metabolism. Together, our results highlight the role of low temperature during clonal growth in alpine plants and provide insights on the molecular mechanisms involved at distinct stages of adventitious rooting.

FLOWERING REPRESSOR AAA+ ATPase 1 is a novel regulator of perennial flowering in Arabis alpina.

Arabis alpina is a polycarpic perennial, in which PERPETUAL FLOWERING1 (PEP1) regulates flowering and perennial traits in a vernalization-dependent manner. Mutagenesis screens of the pep1 mutant established the role of other flowering time regulators in PEP1-parallel pathways. Here we characterized three allelic enhancers of pep1 (eop002, 085 and 091) which flower early. We mapped the causal mutations and complemented mutants with the identified gene. Using quantitative reverse transcriptase PCR and reporter lines, we determined the protein spatiotemporal expression patterns and localization within the cell. We also characterized its role in Arabidopsis thaliana using CRISPR and in A. alpina by introgressing mutant alleles into a wild-type background. These mutants carried lesions in an AAA+ ATPase of unknown function, FLOWERING REPRESSOR AAA+ ATPase 1 (AaFRAT1). AaFRAT1 was detected in the vasculature of young leaf primordia and the rib zone of flowering shoot apical meristems. At the subcellular level, AaFRAT1 was localized at the interphase between the endoplasmic reticulum and peroxisomes. Introgression lines carrying Aafrat1 alleles required less vernalization to flower and reduced number of vegetative axillary branches. By contrast, A. thaliana CRISPR lines showed weak flowering phenotypes. AaFRAT1 contributes to flowering time regulation and the perennial growth habit of A. alpina.

Arabis alpina: A perennial model plant for ecological genomics and life-history evolution.

Many model organisms were chosen and achieved prominence because of an advantageous combination of their life-history characteristics, genetic properties and also practical considerations. Discoveries made in Arabidopsis thaliana, the most renowned noncrop plant model species, have markedly stimulated studies in other species with different biology. Within the family Brassicaceae, the arctic-alpine Arabis alpina has become a model complementary to Arabidopsis thaliana to study the evolution of life-history traits, such as perenniality, and ecological genomics in harsh environments. In this review, we provide an overview of the properties that facilitated the rapid emergence of A. alpina as a plant model. We summarize the evolutionary history of A. alpina, including genomic aspects, the diversification of its mating system and demographic properties, and we discuss recent progress in the molecular dissection of developmental traits that are related to its perennial life history and environmental adaptation. From this published knowledge, we derive open questions that might inspire future research in A. alpina, other Brassicaceae species or more distantly related plant families.

Genetic and Molecular Analysis of Root Hair Development in Arabis alpina.

Root hair formation in Arabidopsis thaliana is a well-established model system for epidermal patterning and morphogenesis in plants. Over the last decades, many underlying regulatory genes and well-established networks have been identified by thorough genetic and molecular analysis. In this study, we used a forward genetic approach to identify genes involved in root hair development in Arabis alpina, a related crucifer species that diverged from A. thaliana approximately 26-40 million years ago. We found all root hair mutant classes known in A. thaliana and identified orthologous regulatory genes by whole-genome or candidate gene sequencing. Our findings indicate that the gene-phenotype relationships regulating root hair development are largely conserved between A. thaliana and A. alpina. Concordantly, a detailed analysis of one mutant with multiple hairs originating from one cell suggested that a mutation in the SUPERCENTIPEDE1 (SCN1) gene is causal for the phenotype and that AaSCN1 is fully functional in A. thaliana. Interestingly, we also found differences in the regulation of root hair differentiation and morphogenesis between the species, and a subset of root hair mutants could not be explained by mutations in orthologs of known genes from A. thaliana. This analysis provides insight into the conservation and divergence of root hair regulation in the Brassicaceae.

The Diverse Roles of FLOWERING LOCUS C in Annual and Perennial Brassicaceae Species.

Most temperate species require prolonged exposure to winter chilling temperatures to flower in the spring. In the Brassicaceae, the MADS box transcription factor FLOWERING LOCUS C (FLC) is a major regulator of flowering in response to prolonged cold exposure, a process called vernalization. Winter annual Arabidopsis thaliana accessions initiate flowering in the spring due to the stable silencing of FLC by vernalization. The role of FLC has also been explored in perennials within the Brassicaceae family, such as Arabis alpina. The flowering pattern in A. alpina differs from the one in A. thaliana. A. alpina plants initiate flower buds during vernalization but only flower after subsequent exposure to growth-promoting conditions. Here we discuss the role of FLC in annual and perennial Brassicaceae species. We show that, besides its conserved role in flowering, FLC has acquired additional functions that contribute to vegetative and seed traits. PERPETUAL FLOWERING 1 (PEP1), the A. alpina FLC ortholog, contributes to the perennial growth habit. We discuss that PEP1 directly and indirectly, regulates traits such as the duration of the flowering episode, polycarpic growth habit and shoot architecture. We suggest that these additional roles of PEP1 are facilitated by (1) the ability of A. alpina plants to form flower buds during long-term cold exposure, (2) age-related differences between meristems, which enable that not all meristems initiate flowering during cold exposure, and (3) differences between meristems in stable silencing of PEP1 after long-term cold, which ensure that PEP1 expression levels will remain low after vernalization only in meristems that commit to flowering during cold exposure. These features result in spatiotemporal seasonal changes of PEP1 expression during the A. alpina life cycle that contribute to the perennial growth habit. FLC and PEP1 have also been shown to influence the timing of another developmental transition in the plant, seed germination, by influencing seed dormancy and longevity. This suggests that during evolution, FLC and its orthologs adopted both similar and divergent roles to regulate life history traits. Spatiotemporal changes of FLC transcript accumulation drive developmental decisions and contribute to life history evolution.

Beyond flowering time: diverse roles of an APETALA2-like transcription factor in shoot architecture and perennial traits.

Polycarpic perennials maintain vegetative growth after flowering. PERPETUAL FLOWERING 1 (PEP1), the orthologue of FLOWERING LOCUS C (FLC) in Arabis alpina regulates flowering and contributes to polycarpy in a vernalisation-dependent pathway. pep1 mutants do not require vernalisation to flower and have reduced return to vegetative growth as all of their axillary branches become reproductive. To identify additional genes that regulate flowering and contribute to perennial traits we performed an enhancer screen of pep1. Using mapping-by-sequencing, we cloned a mutant (enhancer of pep1-055, eop055), performed transcriptome analysis and physiologically characterised the role it plays on perennial traits in an introgression line carrying the eop055 mutation and a functional PEP1 wild-type allele. eop055 flowers earlier than pep1 and carries a lesion in the A. alpina orthologue of the APETALA2 (AP2)-like gene, TARGET OF EAT2 (AaTOE2). AaTOE2 is a floral repressor and acts upstream of SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 5 (AaSPL5). In the wild-type background, which requires cold treatment to flower, AaTOE2 regulates the age-dependent response to vernalisation. In addition, AaTOE2 ensures the maintenance of vegetative growth by delaying axillary meristem initiation and repressing flowering of axillary buds before and during cold exposure. We conclude that AaTOE2 is instrumental in fine tuning different developmental traits in the perennial life cycle of A. alpina.

Natural Variation in Adventitious Rooting in the Alpine Perennial Arabis alpina.

Arctic alpine species follow a mixed clonal-sexual reproductive strategy based on the environmental conditions at flowering. Here, we explored the natural variation for adventitious root formation among genotypes of the alpine perennial Arabis alpina that show differences in flowering habit. We scored the presence of adventitious roots on the hypocotyl, main stem and axillary branches on plants growing in a long-day greenhouse. We also assessed natural variation for adventitious rooting in response to foliar auxin spray. In both experimental approaches, we did not detect a correlation between adventitious rooting and flowering habit. In the greenhouse, and without the application of synthetic auxin, the accession Wca showed higher propensity to produce adventitious roots on the main stem compared to the other accessions. The transcript accumulation of the A. alpina homologue of the auxin inducible GH3.3 gene (AaGH3.3) on stems correlated with the adventitious rooting phenotype of Wca. Synthetic auxin, 1-Naphthaleneacetic acid (1-NAA), enhanced the number of plants with adventitious roots on the main stem and axillary branches. A. alpina plants showed an age-, dosage- and genotype-dependent response to 1-NAA. Among the genotypes tested, the accession Dor was insensitive to auxin and Wca responded to auxin on axillary branches.

Vernalization shapes shoot architecture and ensures the maintenance of dormant buds in the perennial Arabis alpina.

Perennials have a complex shoot architecture with axillary meristems organized in zones of differential bud activity and fate. This includes zones of buds maintained dormant for multiple seasons and used as reservoirs for potential growth in case of damage. The shoot of Arabis alpina, a perennial relative of Arabidopsis thaliana, consists of a zone of dormant buds placed between subapical vegetative and basal flowering branches. This shoot architecture is shaped after exposure to prolonged cold, required for flowering. To understand how vernalization ensures the maintenance of dormant buds, we performed physiological and transcriptome studies, followed the spatiotemporal changes of auxin, and generated transgenic plants. Our results demonstrate that the complex shoot architecture in A. alpina is shaped by its flowering behavior, specifically the initiation of inflorescences during cold treatment and rapid flowering after subsequent exposure to growth-promoting conditions. Dormant buds are already formed before cold treatment. However, dormancy in these buds is enhanced during, and stably maintained after, vernalization by a BRC1-dependent mechanism. Post-vernalization, stable maintenance of dormant buds is correlated with increased auxin response, transport, and endogenous indole-3-acetic acid levels in the stem. Here, we provide a functional link between flowering and the maintenance of dormant buds in perennials.

Genetic and molecular analysis of trichome development in Arabis alpina.

The genetic and molecular analysis of trichome development in Arabidopsis thaliana has generated a detailed knowledge about the underlying regulatory genes and networks. However, how rapidly these mechanisms diverge during evolution is unknown. To address this problem, we used an unbiased forward genetic approach to identify most genes involved in trichome development in the related crucifer species Arabisalpina In general, we found most trichome mutant classes known in A. thaliana We identified orthologous genes of the relevant A. thaliana genes by sequence similarity and synteny and sequenced candidate genes in the A. alpina mutants. While in most cases we found a highly similar gene-phenotype relationship as known from Arabidopsis, there were also striking differences in the regulation of trichome patterning, differentiation, and morphogenesis. Our analysis of trichome patterning suggests that the formation of two classes of trichomes is regulated differentially by the homeodomain transcription factor AaGL2 Moreover, we show that overexpression of the GL3 basic helix-loop-helix transcription factor in A. alpina leads to the opposite phenotype as described in A. thaliana Mathematical modeling helps to explain how this nonintuitive behavior can be explained by different ratios of GL3 and GL1 in the two species.

Seed traits are pleiotropically regulated by the flowering time gene PERPETUAL FLOWERING 1 (PEP1) in the perennial Arabis alpina.

The life cycles of plants are characterized by two major life history transitions-germination and the initiation of flowering-the timing of which are important determinants of fitness. Unlike annuals, which make the transition from the vegetative to reproductive phase only once, perennials iterate reproduction in successive years. The floral repressor PERPETUAL FLOWERING 1 (PEP1), an ortholog of FLOWERING LOCUS C, in the alpine perennial Arabis alpina ensures the continuation of vegetative growth after flowering and thereby restricts the duration of the flowering episode. We performed greenhouse and garden experiments to compare flowering phenology, fecundity and seed traits between A. alpina accessions that have a functional PEP1 allele and flower seasonally and pep1 mutants and accessions that carry lesions in PEP1 and flower perpetually. In the garden, perpetual genotypes flower asynchronously and show higher winter mortality than seasonal ones. PEP1 also pleiotropically regulates seed dormancy and longevity in a way that is functionally divergent from FLC. Seeds from perpetual genotypes have shallow dormancy and reduced longevity regardless of whether they after-ripened in plants grown in the greenhouse or in the experimental garden. These results suggest that perpetual genotypes have higher mortality during winter but compensate by showing higher seedling establishment. Differences in seed traits between seasonal and perpetual genotypes are also coupled with differences in hormone sensitivity and expression of genes involved in hormonal pathways. Our study highlights the existence of pleiotropic regulation of seed traits by hub developmental regulators such as PEP1, suggesting that seed and flowering traits in perennial plants might be optimized in a coordinated fashion.

PERPETUAL FLOWERING2 coordinates the vernalization response and perennial flowering in Arabis alpina.

The floral repressor APETALA2 (AP2) in Arabidopsis regulates flowering through the age pathway. The AP2 ortholog in the alpine perennial Arabis alpina, PERPETUAL FLOWERING 2 (PEP2), was previously reported to control flowering through the vernalization pathway via enhancing the expression of another floral repressor PERPETUAL FLOWERING 1 (PEP1), the ortholog of Arabidopsis FLOWERING LOCUS C (FLC). However, PEP2 also regulates flowering independently of PEP1. To characterize the function of PEP2, we analyzed the transcriptomes of pep2 and pep1 mutants. The majority of differentially expressed genes were detected between pep2 and the wild type or between pep2 and pep1, highlighting the importance of the PEP2 role that is independent of PEP1. Here, we demonstrate that PEP2 activity prevents the up-regulation of the A. alpina floral meristem identity genes FRUITFUL (AaFUL), LEAFY (AaLFY), and APETALA1 (AaAP1), ensuring floral commitment during vernalization. Young pep2 seedlings respond to vernalization, suggesting that PEP2 regulates the age-dependent response to vernalization independently of PEP1. The major role of PEP2 through the PEP1-dependent pathway takes place after vernalization, when it facilitates PEP1 activation both in the main shoot apex and in axillary branches. These multiple roles of PEP2 in the vernalization response contribute to the A. alpina life cycle.

Extended Vernalization Regulates Inflorescence Fate in Arabis alpina by Stably Silencing PERPETUAL FLOWERING1.

The alpine perennial Arabis alpina initiates flower buds during prolonged exposure to cold. In the accession Pajares, we demonstrate that the length of vernalization influences flowering time and inflorescence fate but does not affect the axillary branches that maintain vegetative growth. The expression of floral organ identity genes gradually increases in the main shoot apex during vernalization, correlating with an increase in floral commitment. In northern Arabidopsis (Arabidopsis thaliana) accessions, the length of vernalization modulates the stable silencing of the floral repressor FLOWERING LOCUS C (FLC). We demonstrate that expression of PERPETUAL FLOWERING1 (PEP1), the ortholog of FLC in A. alpina, is similarly influenced by the duration of the exposure to cold. Extended vernalization results in stable silencing of PEP1 in the inflorescence. In contrast, insufficient vernalization leads to PEP1 reactivation after cold treatment, which correlates with delayed flowering and the appearance of floral reversion phenotypes such as bracts and vegetative inflorescence branches. Floral reversion phenotypes are reduced in the pep1-1 mutant, suggesting that PEP1 regulates the fate of the inflorescence after vernalization. The effect of vernalization duration on stable silencing of PEP1 is specific to meristems that initiate flowering during cold treatment. Extended vernalization fails to silence PEP1 in young seedlings and axillary branches that arise from buds initiated during cold treatment, which remain vegetative. We conclude that the duration of vernalization in A. alpina differentially regulates PEP1 in the inflorescence and axillary branches. PEP1 has a dual role regulating meristem fate; it prevents meristems from flowering and antagonizes inflorescence development after vernalization.

Oxygen-Glucose Deprivation (OGD) Modulates the Unfolded Protein Response (UPR) and Inflicts Autophagy in a PC12 Hypoxia Cell Line Model.

Hypoxia is the lack of sufficient oxygenation of tissue, imposing severe stress upon cells. It is a major feature of many pathological conditions such as stroke, traumatic brain injury, cerebral hemorrhage, perinatal asphyxia and can lead to cell death due to energy depletion and increased free radical generation. The present study investigates the effect of hypoxia on the unfolded protein response of the cell (UPR), utilizing a 16-h oxygen-glucose deprivation protocol (OGD) in a PC12 cell line model. Expression of glucose-regulated protein 78 (GRP78) and glucose-regulated protein 94 (GRP94), key players of the UPR, was studied along with the expression of glucose-regulated protein 75 (GRP75), heat shock cognate 70 (HSC70), and glyceraldehyde 3-phosphate dehydrogenase, all with respect to the cell death mechanism(s). Cells subjected to OGD displayed upregulation of GRP78 and GRP94 and concurrent downregulation of GRP75. These findings were accompanied with minimal apoptotic cell death and induction of autophagy. The above observation warrants further investigation to elucidate whether autophagy acts as a pro-survival mechanism that upon severe and prolonged hypoxia acts as a concerted cell response leading to cell death. In our OGD model, hypoxia modulates UPR and induces autophagy.

Low Dose Administration of Glutamate Triggers a Non-Apoptotic, Autophagic Response in PC12 Cells.

BACKGROUND/AIMS: Increasing amounts of the neurotransmitter glutamate are associated with excitotoxicity, a phenomenon related both to homeostatic processes and neurodegenerative diseases such as multiple sclerosis. METHODS: PC12 cells (rat pheochromocytoma) were treated with various concentrations of the non-essential amino acid glutamate for 0.5-24 hours. The effect of glutamate on cell morphology was monitored with electron microscopy and haematoxylin-eosin staining. Cell survival was calculated with the MTT assay. Expression analysis of chaperones associated with the observed phenotype was performed using either Western Blotting at the protein level or qRT-PCR at the mRNA level. RESULTS: Administration of glutamate in PC12 cells in doses as low as 10 µM causes an up-regulation of GRP78, GRP94 and HSC70 protein levels, while their mRNA levels show the opposite kinetics. At the same time, GAPDH and GRP75 show reduced protein levels, irrespective of their transcriptional rate. On a cellular level, low concentrations of glutamate induce an autophagy-mediated pro-survival phenotype, which is further supported by induction of the autophagic marker LC3. CONCLUSION: The findings in the present study underline a discrete effect of glutamate on neuronal cell fate depending on its concentration. It was also shown that a low dose of glutamate orchestrates a unique expression signature of various chaperones and induces cell autophagy, which acts in a neuroprotective fashion.

Genome expansion of Arabis alpina linked with retrotransposition and reduced symmetric DNA methylation.

Despite evolutionary conserved mechanisms to silence transposable element activity, there are drastic differences in the abundance of transposable elements even among closely related plant species. We conducted a de novo assembly for the 375 Mb genome of the perennial model plant, Arabis alpina. Analysing this genome revealed long-lasting and recent transposable element activity predominately driven by Gypsy long terminal repeat retrotransposons, which extended the low-recombining pericentromeres and transformed large formerly euchromatic regions into repeat-rich pericentromeric regions. This reduced capacity for long terminal repeat retrotransposon silencing and removal in A. alpina co-occurs with unexpectedly low levels of DNA methylation. Most remarkably, the striking reduction of symmetrical CG and CHG methylation suggests weakened DNA methylation maintenance in A. alpina compared with Arabidopsis thaliana. Phylogenetic analyses indicate a highly dynamic evolution of some components of methylation maintenance machinery that might be related to the unique methylation in A. alpina.

Functional aspects of the EGF-induced MAP kinase cascade: a complex self-organizing system approach.

The EGF-induced MAP kinase cascade is one of the most important and best characterized networks in intracellular signalling. It has a vital role in the development and maturation of living organisms. However, when deregulated, it is involved in the onset of a number of diseases. Based on a computational model describing a "surface" and an "internalized" parallel route, we use systems biology techniques to characterize aspects of the network's functional organization. We examine the re-organization of protein groups from low to high external stimulation, define functional groups of proteins within the network, determine the parameter best encoding for input intensity and predict the effect of protein removal to the system's output response. Extensive functional re-organization of proteins is observed in the lower end of stimulus concentrations. As we move to higher concentrations the variability is less pronounced. 6 functional groups have emerged from a consensus clustering approach, reflecting different dynamical aspects of the network. Mutual information investigation revealed that the maximum activation rate of the two output proteins best encodes for stimulus intensity. Removal of each protein of the network resulted in a range of graded effects, from complete silencing to intense activation. Our results provide a new "vista" of the EGF-induced MAP kinase cascade, from the perspective of complex self-organizing systems. Functional grouping of the proteins reveals an organizational scheme contrasting the current understanding of modular topology. The six identified groups may provide the means to experimentally follow the dynamics of this complex network. Also, the vulnerability analysis approach may be used for the development of novel therapeutic targets in the context of personalized medicine.

Rituximab en el tratamiento del síndrome del pulmón encogido del lupus eritematoso sistémico / Rituximab in the treatment of shrinking lung syndrome in systemic lupus erythematosus

El síndrome del pulmón encogido (SPE) es una manifestación poco frecuente del lupus eritematoso sistémico. Exponemos el caso de una paciente afectada de SPE, refractario al tratamiento con glucocorticoides e inmunosupresores, que tras el inicio de tratamiento con rituximab presentó marcada mejoría de los síntomas. Aunque la evidencia es escasa, el tratamiento con rituximab podría ser propuesto en el SPE cuando fracasa el tratamiento clásico (AU)

Shrinking lung syndrome (SLS) is a rare manifestation of systemic lupus erythematosus. We report the case of a patient with non-responding SLS (neither to glucocorticoids nor immunosupresors), who showed remarkable improvement after the onset of treatment with rituximab. Although there is a little evidence, treatment with rituximab could be proposed in SLS when classical treatment fails (AU)

Evolutionary conservation of cold-induced antisense RNAs of FLOWERING LOCUS C in Arabidopsis thaliana perennial relatives.

Antisense RNA (asRNA) COOLAIR is expressed at A. thaliana FLOWERING LOCUS C (FLC) in response to winter temperatures. Its contribution to cold-induced silencing of FLC was proposed but its functional and evolutionary significance remain unclear. Here we identify a highly conserved block containing the COOLAIR first exon and core promoter at the 3' end of several FLC orthologues. Furthermore, asRNAs related to COOLAIR are expressed at FLC loci in the perennials A. alpina and A. lyrata, although some splicing variants differ from A. thaliana. Study of the A. alpina orthologue, PERPETUAL FLOWERING 1 (PEP1), demonstrates that AaCOOLAIR is induced each winter of the perennial life cycle. Introduction of PEP1 into A. thaliana reveals that AaCOOLAIR cis-elements confer cold-inducibility in this heterologous species while the difference between PEP1 and FLC mRNA patterns depends on both cis-elements and species-specific trans-acting factors. Thus, expression of COOLAIR is highly conserved, supporting its importance in FLC regulation.

Chronic massive rotator cuff tear in rats: in vivo evaluation of muscle force and three-dimensional histologic analysis.

BACKGROUND: Massive rotator cuff tear repair is frequently complicated by unsatisfactory clinical results due to possible tendon retraction, muscle atrophy, and fatty degeneration. The objective of this study was the development of a chronic massive tear in a rat model and the evaluation of the muscle force in vivo and of the histologic changes in a 3- dimensional manner. METHODS: To simulate massive rotator cuff tears, both the supraspinatus (SS) and the infraspinatus (IS) tendons were surgically detached from the right humerus of 15 male adult Sprague-Dawley rats. Twelve weeks postoperatively, all animals underwent isometric tension recordings of both the SS and IS muscles. Histologic analysis and image deconvolution processing were performed to estimate the presence and the distribution of atrophy in 3 dimensions. RESULTS: An overall 30% and 35% reduction in muscle force of the SS and IS muscles, respectively, was observed compared with the left uninjured shoulder (P < .005). Histologic analysis revealed that the degeneration and the fatty infiltration were more evident near the tendon and at the dorsal side in both muscle groups. CONCLUSIONS: These results show that functional impairment of SS and IS muscles after chronic massive tendon tears could be attributed to the decrease in muscle force production during their repair on the greater tuberosity and, second, to the comparatively greater degeneration of their dorsal part.

Analysis of TTG1 function in Arabis alpina.

BACKGROUND: In Arabidopsis thaliana (A. thaliana) the WD40 protein TRANSPARENT TESTA GLABRA1 (TTG1) controls five traits relevant for the adaptation of plants to environmental changes including the production of proanthocyanidin, anthocyanidin, seed coat mucilage, trichomes and root hairs. The analysis of different Brassicaceae species suggests that the function of TTG1 is conserved within the family. RESULTS: In this work, we studied the function of TTG1 in Arabis alpina (A. alpina). A comparison of wild type and two Aattg1 alleles revealed that AaTTG1 is involved in the regulation of all five traits. A detailed analysis of the five traits showed striking phenotypic differences between A. alpina and A. thaliana such that trichome formation occurs also at later stages of leaf development and that root hairs form at non-root hair positions. CONCLUSIONS: The evolutionary conservation of the regulation of the five traits by TTG1 on the one hand and the striking phenotypic differences make A. alpina a very interesting genetic model system to study the evolution of TTG1-dependent gene regulatory networks at a functional level.