Changes in pressure pain thresholds over C5-C6 zygapophyseal joint after a cervicothoracic junction manipulation in healthy subjects

OBJECTIVE

This study examines if C7-T1 manipulation results in changes in pressure pain thresholds (PPT) over bilateral C5-C6 zygapophyseal joints in asymptomatic subjects.

METHODS

Thirty subjects, 13 men and 17 women, without a current history of neck, shoulder, or upper extremity pain participated. Participants were randomly divided into 3 groups: experimental dominant group, subjects who received the manipulative thrust directed at the right side of the C7-T1 joint; experimental nondominant group, those who received the thrust on the left side of the C7-T1 joint; and a placebo group, those who received a sham-manual procedure. The outcome measure was the PPT on both right and left C5-C5 zygapophyseal joints, which was assessed at preintervention and 5 minutes postintervention by an assessor blinded to the treatment allocation of the subject. A 3-way repeated measures analysis of covariance was used to evaluate changes in PPT.

RESULTS

The analysis of covariance revealed time x group (F = 32.3; P < .001), time x side (F = 4.9; P < .05), time x sex (F = 7.93; P < .01), and time x group x sex (F = 7.606; P < .001) interactions. Post hoc analyses found that (a) both experimental groups showed greater improvements in PPT than the placebo group (P < .05), without significant differences between them (P > .6); (b) the right side had greater increases in PPT in both experimental groups (P < .05), but not within the placebo group (P > .8); (c) men experienced greater increases in PPT levels than women, particularly in the experimental nondominant group (P < .01). Within-group effect sizes were large for both experimental groups (d > 1), but small for the placebo condition (d < 0.2).

CONCLUSIONS

These results suggest that a C7-T1 manipulation induced changes in PPT in both right and left C5-C6 zygapophyseal joints in healthy subjects.

Myofascial trigger points and their relationship to headache clinical parameters in chronic tension-type headache

OBJECTIVE

To assess the presence of trigger points (TrPs) in several head and neck muscles in subjects with chronic tension-type headache (CTTH) and in healthy subjects; and to evaluate the relationship of these TrPs with forward head posture (FHP), headache intensity, duration, and frequency.

BACKGROUND

Tension-type headache (TTH) is a headache in which myofascial TrPs in head and neck muscles might play an important etiologic role.

DESIGN

A blinded, controlled, pilot study.

METHODS

Twenty-five CTTH subjects and 25 matched controls without headache were studied. TrPs in bilateral upper trapezius, sternocleidomastoids, and temporalis muscles were identified according to Simons et al's diagnostic criteria: tenderness in a hyperirritable spot within a palpable taut band, local twitch response elicited by snapping palpation, and elicited referred pain with palpation. A TrP was considered active if the subject recognized the evoked referred pain as familiar headache. If the evoked referred pain was not recognized as familiar headache, the TrP was considered as latent. Side-view pictures of each subject were taken in both sitting and standing positions in order to assess FHP by measuring the cranio-vertebral angle. Both measurements were made by a blinded assessor. A headache diary was kept for 4 weeks in order to assess headache intensity, frequency, and duration.

RESULTS

The mean number of TrPs on each CTTH subject was 3.9 (SD: 1.2), of which 1.9 (SD: 1.2) were active TrPs and 1.9 (SD: 0.8) were latent TrPs. Control subjects only exhibited latent TrPs (mean: 1.4; SD: 0.8). There was a significant difference between the CTTH group and the controls for active TrPs (P < .001), but not for latent TrPs (P > .05). Differences in the distribution of active and latent TrPs within each muscle were also significant for all the analyzed muscles (P < .01). CTTH subjects with active TrPs in the right upper trapezius muscle or left sternocleidomastoid muscle showed a greater headache intensity and duration, but not headache frequency, compared to those with latent TrPs (P < .05). Active TrPs in the right temporalis muscle were associated with longer headache duration (P < .01), whereas active TrPs in the left temporalis muscle were associated with greater headache intensity (P < .05). CTTH subjects with active TrPs in the analyzed muscles had a greater FHP than those with latent TrPs in both sitting and standing positions. Differences were only significant for TrPs in the left sternocleidomastoid and FHP in the sitting position (P < .01).

CONCLUSIONS

Active TrPs in upper trapezius, sternocleidomastoid, and temporalis muscles were associated with CTTH. CTTH subjects with active TrPs usually reported a greater headache intensity and longer headache duration than those with latent TrPs. CTTH subjects with active TrPs tended to have a greater FHP than CTTH subjects with latent TrPs.

One-year follow-up of two exercise interventions for the management of patients with ankylosing spondylitis: a randomized controlled trial

OBJECTIVE

To assess the long-term effects on functional and mobility outcomes of two exercise interventions for the management of patients with ankylosing spondylitis.

DESIGN

In an extended 12-mo follow-up of a randomized controlled trial, 40 patients who were diagnosed with ankylosing spondylitis according to the modified criteria of New York, allocated to control or experimental groups using a random numbers table, and who performed their respective exercise program at least three times per month, were included in this long-term study. The control group was treated during 15 sessions with a conventional exercise regimen in ankylosing spondylitis, whereas the experimental group received 15 sessions of exercises based on the treatment of the shortened muscle chains following the guidelines described by the Global Posture Reeducation method. These patients were followed up and assessed again 1 yr after entering the study, re-applying the same validated indexes: BASMI (Bath Ankylosing Spondylitis Metrology Index [tragus to wall distance, modified Schober test, cervical rotation, lumbar side flexion, and intermalleolar distance]), BASDAI (Bath Ankylosing Spondylitis Disease Activity Index), and BASFI (Bath Ankylosing Spondylitis Functional Index).

RESULTS

The intragroup comparison between follow-up and post-intervention data showed that both groups decrease their clinical and functional measures during the follow-up period. This decrease was only significant for lumbar side flexion and intermalleolar distance measurements, being more significant in the control group (P = 0.001 and P = 0.002, respectively). Intragroup differences between follow-up and pre-intervention assessments revealed that improvements in all mobility measures of the BASMI index and in the BASFI index were partially maintained at the 12-mo follow-up in the experimental group but not in the control group. The intergroup comparison (unpaired t test analysis) between changes on each outcome during the long-term follow-up (post-follow-up; and pre-follow-up) showed no significant differences in the decrease between post-intervention and follow-up data between the study groups. On the other hand, the intergroup comparison between pre-intervention and follow-up data revealed significant differences in almost all mobility measures of the BASMI index (except for cervical rotation) and in the BASFI index, in favor of the experimental group.

CONCLUSIONS

An exercise regimen based on the Global Posture Reeducation method and focusing on specific strengthening and flexibility exercises of the shortened muscle chains offers promising short- and long-term results in the management of patients who have ankylosing spondylitis.

Trigger points in the suboccipital muscles and forward head posture in tension-type headache

OBJECTIVE

To assess the presence of trigger points (TrPs) in the suboccipital muscles and forward head posture (FHP) in subjects with chronic tension-type headache (CTTH) and in healthy subjects, and to evaluate the relationship of TrPs and FHP with headache intensity, duration, and frequency.

BACKGROUND

Tension-type headache (TTH) is a prototypical headache in which myofascial TrPs in the cervical and pericranial musculature can play an important role.

DESIGN

A blinded, controlled pilot study.

METHODS

Twenty CTTH subjects and 20 matched controls without headache participated. TrPs were identified by eliciting referred pain with palpation, and increased referred pain with muscle contraction. Side-view pictures of each subject were taken in sitting and standing positions, in order to assess FHP by measuring the craniovertebral angle. Both measures were taken by a blinded assessor. A headache diary was kept for 4 weeks in order to assess headache intensity, frequency, and duration.

RESULTS

Sixty-five percent (13/20) CTTH subjects showed active TrPs and 35% (7/20) had latent TrPs in the suboccipital muscles. Six (30%) controls also had latent TrPs. Differences in the presence of suboccipital muscle TrPs between both the groups were significant for active TrPs (P < .001) but not for latent TrPs (P > .5). CTTH subjects with active TrPs reported a greater headache intensity and frequency than those with latent TrPs (P < .05). The degree of FHP was greater in CTTH subjects than in controls in both sitting and standing positions (P < .01). Within the CTTH group, there was a negative correlation between the craniovertebral angle and the frequency of headache (r(s) = -0.6, P < .01, in sitting position; r(s) = -0.5, P < .05, in standing position). CTTH subjects with active TrPs had a greater FHP than those with latent TrPs, though this difference was not significant.

CONCLUSIONS

Suboccipital active TrPs and FHP were associated with CTTH. CCTH subjects with active TrPs reported a greater headache intensity and frequency than those with latent TrPs. The degree of FHP correlated positively with headache duration, headache frequency, and the presence of suboccipital active TrPs.

Myofascial trigger points in the suboccipital muscles in episodic tension-type headache

Referred pain evoked by suboccipital muscle trigger points (TrPs) spreads to the side of the head over the occipital and temporal bones and is usually perceived as bilateral headache. This paper describes the presence of referred pain from suboccipital muscle TrPs in subjects with episodic tension-type headache (ETTH) and in healthy controls. Ten patients presenting with ETTH and 10 matched controls without headache were examined by a blinded assessor for the presence of suboccipital muscle TrPs. Diagnostic criteria described by Simons and Gerwin were adapted to diagnose TrPs, i.e. presence of tenderness in the suboccipital region, referred pain evoked by maintained pressure for 10 s, and increased referred pain on muscle contraction. Six ETTH patients (60%) had active TrPs and 4 had latent TrPs (40%). On the other hand, 2 control subjects also had latent TrPs. Differences in the presence of suboccipital muscle TrPs between both groups were significant for active TrPs (P<0.001), but not for latent TrPs. Active TrPs were only present in ETTH patients, although TrP activity was not related to any clinical variable concerning the intensity and the temporal profile of headache. Myofascial TrPs in the suboccipital muscles might contribute to the origin and/or maintenance of headache, but a comprehensive knowledge of the role of these muscles in tension-type headache awaits further research.

Forward head posture and neck mobility in chronic tension-type headache: a blinded, controlled study

Forward head posture (FHP) and neck mobility were objectively assessed in 25 patients with chronic tension-type headache (CTTH) and 25 healthy controls. Side-view pictures were taken in a sitting position to measure the cranio-vertebral angle. A cervical goniometer was employed to measure the range of all cervical motions. Patients with CTTH showed a smaller cranio-vertebral angle (45.3 degrees +/- 7.6 degrees) than controls (54.1 degrees +/- 6.3 degrees), thus presenting a greater FHP (P < 0.001). Patients also had lesser neck mobility for all cervical movements, except for right lateral flexion (P < 0.01). There was a positive correlation between the cranio-vertebral angle and neck mobility. Within the CTTH group, a negative correlation was found between the cranio-vertebral angle and headache frequency, but neck mobility did not correlate with headache parameters. Further research is needed to define a potential role of FHP and restricted neck mobility in the origin or maintenance of TTH.

Are Manual Therapies Effective in Reducing Pain From Tension-Type Headache?

OBJECTIVES

A systematic review was performed to establish whether manual therapies have specific efficacy in reducing pain from tension-type headache (TTH).

METHODS

Computerized literature searches were performed in MEDLINE, EMBASE, AMED, MANTIS, CINAHL, PEDro, and Cochrane databases. Papers were included if they described clinical (open noncontrolled studies) or randomized controlled trials in which any form of manual therapy was used for TTH, and if they were published after 1994 in the English language. The methodologic quality of the trials was assessed using the PEDro scale. Levels of scientific evidence, based on the quality and the outcomes of the studies, were established for each manual therapy: strong, moderate, limited, and inconclusive evidence.

RESULTS

Only six studies met the inclusion criteria. These trials evaluated different manual therapy modalities: spinal manipulation (three trials), classic massage (one trial), connective tissue manipulation (two trials), soft tissue massage (one trial), Dr. Cyriax's vertebral mobilization (one trial), manual traction (one trial), and CV-4 craniosacral technique (one trial). Methodologic PEDro quality scores ranged from 2 to 8 points out of a theoretical maximum of 10 points (mean=5.8+/-2.1). Analysis of the quality and the outcomes of all trials did not provide rigorous evidence that manual therapies have a positive effect in reducing pain from TTH: spinal manipulative therapy showed inconclusive evidence of effectiveness (level 4), whereas soft tissue techniques showed limited evidence (level 3).

CONCLUSIONS

The authors found no rigorous evidence that manual therapies have a positive effect in the evolution of TTH. The most urgent need for further research is to establish the efficacy beyond placebo of the different manual therapies currently applied in patients with TTH.

Methodological quality of randomized controlled trials of spinal manipulation and mobilization in tension-type headache, migraine, and cervicogenic headache

STUDY DESIGN

Literature review of quality of clinical trials.

OBJECTIVE

To determine the methodological quality of published randomized controlled trials that used spinal manipulation and/or mobilization to treat patients with tension-type headache (TTH), cervicogenic headache (CeH), and migraine (M) in the last decade.

BACKGROUND

TTH, CeH, and M are the most prevalent types of headaches seen in adults. Individuals who have headaches frequently use physical therapy, manual therapy, or chiropractic care. Randomized controlled trials are considered an optimal method with which to assess the efficacy of any intervention.

METHODS

Computerized literature searches were performed in MEDLINE, EMBASE, COCHRANE, AMED, MANTIS, CINHAL, and PEDro databases. Randomized controlled trials in which spinal manipulation and/or mobilization had been used for TTH, CeH, and M published in a peer-reviewed journal as full text, and with at least 1 clinically relevant outcome measure (ie, headache intensity, duration, or frequency) were reviewed. The methodological quality of the studies was assessed independently by 2 reviewers using a set of predefined criteria.

RESULTS

Only 8 studies met all the inclusion criteria. One clinical trial evaluated spinal manipulation and mobilization together, and the remaining 7 assessed spinal manipulative therapy. No controlled trials analyzing exclusively the effects of spinal mobilization were found. Methodological scores ranged from 35 to 56 points out of a theoretical maximum of 100 points, indicating an overall poor methodology of the studies. Only 2 studies obtained a high-quality score (greater than 50 points). No significant differences in quality scores were found based on the type of headache investigated. Methodological quality was not associated with the year of publication (before 2000, or later) nor with the results (positive, neutral, negative) reported in the studies. The most common flaws were a small sample size, the absence of a placebo control group, lack of blinded patients, and no description of the manipulative procedure.

CONCLUSIONS

There are few published randomized controlled trials analyzing the effectiveness of spinal manipulation and/or mobilization for TTH, CeH, and M in the last decade. In addition, the methodological quality of these papers is typically low. Clearly, there is a need for high-quality randomized controlled trials assessing the effectiveness of these interventions in these headache disorders.

Spinal manipulative therapy in the management of cervicogenic headache

Patients suffering from cervicogenic headache (CeH) are commonly treated with spinal manipulative therapy. We have analyzed the quality and the outcomes of published, randomized, controlled trials assessing the effectiveness of spinal manipulation in CeH. Among 121 relevant articles, only two met all the inclusion criteria. Methodological quality scores were 8/10 and 7/10 points. Only one of the trials made use of a headache diary. Both the trials reported positive (+) results on headache intensity, headache duration, and medication intake, so that spinal manipulative therapy obtained strong evidence of effectiveness (level 1) with regard to these outcomes. Conversely, spinal manipulation obtained no more than limited evidence (level 3) in reducing headache frequency, as it was analyzed only in one study with positive (+) results. A greater number of well-designed, randomized, controlled trials are required to confirm or refute the effectiveness of spinal manipulation in the management of CeH.

Two Exercise Interventions for the Management of Patients with Ankylosing Spondylitis

OBJECTIVE

The purpose of this clinical trial was to evaluate the impact of a 4-month comprehensive protocol of strengthening and flexibility exercises developed by our research group versus conventional exercises for patients with Ankylosing Spondylitis (AS) on functional and mobility outcomes.

DESIGN

Randomized controlled trial. Forty-five patients diagnosed with AS according to the modified criteria of New York were allocated to control or experimental groups using a random numbers table. The control group was treated with a conventional protocol of physical therapy in AS, whereas the experimental group was treated with the protocol suggested by our research group. The conventional intervention consisted of 20 exercises: motion and flexibility exercises of the cervical, thoracic, and lumbar spine; stretching of the shortened muscles; and chest expansion exercises. The experimental protocol is based on the postural affectation of the AS and the treatment of the shortened muscle chains in these patients according to the Global Posture Reeducation (GPR) method. This intervention employs specific strengthening and flexibility exercises in which the shortened muscle chains are stretched and strengthened. The study lasted 4 mos. During this period, patients received a weekly group session managed by an experienced physiotherapist. Each session lasted an hour, and there were 15 total sessions. Changes in activity, mobility, and functional capacity were evaluated by an assessor blinded to the intervention, using the following previously validated scores from the Bath group: BASMI (tragus to wall distance, modified Schober test, cervical rotation, lumbar side flexion, and intermalleolar distance), BASDAI (The Bath Ankylosing Spondylitis Disease Activity Index), and BASFI (The Bath Ankylosing Spondylitis Functional Index).

RESULTS

Both groups showed an improvement (prepost scores) in all the outcome measures, mobility measures of the BASMI index, as well as in BASFI and BASDAI indexes. In the control group, the improvement in tragus to wall distance (P=0.009) and in lumbar side flexion (P=0.02) was statistically significant. Although the rest of the outcomes also improved, they did not reach a significant level (P>0.05). In the experimental group, the improvement in all the clinical measures of the BASMI index (P<0.01) and in the BASFI index (P=0.003) was statistically significant. The intergroup comparison between the improvement (prepost scores) in both groups showed that the experimental group obtained a greater improvement than the control group in all the clinical measures of the BASMI index, except in tragus to wall distance, as well as in the BASFI index.

CONCLUSIONS

The experimental protocol developed by our research group, based on the GPR method and specific strengthening and flexibility exercises of the muscle chains, offers promising results in the management of patients suffering from AS. Further trials on this topic are required.

Pleiotropic effects of the Arabidopsis cryptochrome 2 allelic variation underlie fruit trait-related QTL

The previous molecular identification of a flowering time QTL segregating in the Arabidopsis L er x Cvi cross, demonstrated that natural allelic variation at the blue light photoreceptor CRY2 gene affects flowering time (El-Assal et al., 2001). In addition, previous works on the same cross have mapped several QTL affecting other unrelated life history traits in the CRY2 genomic region. In the present report, we have used a set of Arabidopsis L er transgenic plants carrying four different functional CRY2 transgenes for phenotypic analyses, with the aim of exploring the extent of pleiotropy of CRY2 allelic variation. It is concluded that previously identified QTL affecting fruit length, ovule number per fruit, and percentage of unfertilized ovules are caused by this same Ler/Cvi CRY2 allelic variation. In addition, dose effects of the CRY2-L er allele are detected for fruit length. A seed weight QTL at the map position of CRY2 could not be confirmed and also no effect on seed dormancy was observed. Thus, it is shown that transgenic plants carrying different alleles can be a useful tool to attribute QTL for different complex traits to a specific locus, even when the relationship among the traits has not been previously suggested.

A QTL for flowering time in Arabidopsis reveals a novel allele of CRY2

Variation of flowering time is found in the natural populations of many plant species. The underlying genetic variation, mostly of a quantitative nature, is presumed to reflect adaptations to different environments contributing to reproductive success. Analysis of natural variation for flowering time in Arabidopsis thaliana has identified several quantitative trait loci (QTL), which have yet to be characterized at the molecular level. A major environmental factor that determines flowering time is photoperiod or day length, the length of the light period, which changes across the year differently with geographical latitude. We identified the EDI locus as a QTL partly accounting for the difference in flowering response to the photoperiod between two Arabidopsis accessions: the laboratory strain Landsberg erecta (Ler), originating in Northern Europe, and Cvi, collected in the tropical Cape Verde Islands. Positional cloning of the EDI QTL showed it to be a novel allele of CRY2, encoding the blue-light photoreceptor cryptochrome-2 that has previously been shown to promote flowering in long-day (LD) photoperiods. We show that the unique EDI flowering phenotype results from a single amino-acid substitution that reduces the light-induced downregulation of CRY2 in plants grown under short photoperiods, leading to early flowering.

Genetic analysis of seed-soluble oligosaccharides in relation to seed storability of Arabidopsis

Seed oligosaccharides (OSs) and especially raffinose series OSs (RSOs) are hypothesized to play an important role in the acquisition of desiccation tolerance and consequently in seed storability. In the present work we analyzed the seed-soluble OS (sucrose, raffinose, and stachyose) content of several Arabidopsis accessions and thus identified the genotype Cape Verde Islands having a very low RSO content. By performing quantitative trait loci (QTL) mapping in a recombinant inbred line population, we found one major QTL responsible for the practically monogenic segregation of seed stachyose content. This locus also affected the content of the two other OSs, sucrose, and raffinose. Two candidate genes encoding respectively for galactinol synthase and raffinose synthase were located within the genomic region around this major QTL. In addition, three smaller-effect QTL were identified, each one specifically affecting the content of an individual OS. Seed storability was analyzed in the same recombinant inbred line population by measuring viability (germination) under two different seed aging assays: after natural aging during 4 years of dry storage at room temperature and after artificial aging induced by a controlled deterioration test. Thus, four QTL responsible for the variation of this trait were mapped. Comparison of the QTL genetic positions showed that the genomic region containing the major OS locus did not significantly affect the seed storability. We concluded that in the studied material neither RSOs nor sucrose content had a specific effect on seed storability.

The late flowering phenotype of fwa mutants is caused by gain-of-function epigenetic alleles of a homeodomain gene

The transition to flowering in Arabidopsis thaliana is delayed in fwa mutant plants. FWA was identified by loss-of-function mutations in normally flowering revertants of the fwa mutant, and it encodes a homeodomain-containing transcription factor. The DNA sequence of wild-type and fwa mutant alleles was identical in the genomic region of FWA. Furthermore, the FWA gene is ectopically expressed in fwa mutants and silenced in mature wild-type plants. This silencing is associated with extensive methylation of two direct repeats in the 5' region of the gene. The late flowering phenotype, ectopic FWA expression, and hypomethylation of the repeats were also induced in the ddm1 hypomethylated background. Mechanisms for establishment and maintenance of the epigenetic mark on FWA are discussed.

The late flowering phenotype of fwa mutants is caused by gain-of-function epigenetic alleles of a homeodomain gene

The transition to flowering in Arabidopsis thaliana is delayed in fwa mutant plants. FWA was identified by loss-of-function mutations in normally flowering revertants of the fwa mutant, and it encodes a homeodomain-containing transcription factor. The DNA sequence of wild-type and fwa mutant alleles was identical in the genomic region of FWA. Furthermore, the FWA gene is ectopically expressed in fwa mutants and silenced in mature wild-type plants. This silencing is associated with extensive methylation of two direct repeats in the 5' region of the gene. The late flowering phenotype, ectopic FWA expression, and hypomethylation of the repeats were also induced in the ddm1 hypomethylated background. Mechanisms for establishment and maintenance of the epigenetic mark on FWA are discussed.

Naturally occurring variation in Arabidopsis: an underexploited resource for plant genetics

The definition of gene functions requires the phenotypic characterization of genetic variants. Currently, such functional analysis of Arabidopsis genes is based largely on laboratory-induced mutants that are selected in forward and reverse genetic studies. An alternative complementary source of genetic variation is available: the naturally occurring variation among accessions. The multigenic nature of most of this variation has limited its application until now. However, the use of genetic methods developed to map quantitative trait loci, in combination with the characteristics and resources available for molecular biology in Arabidopsis, allow this variation to be exploited up to the molecular level. Here, we describe the current tools available for the forward genetic analysis of this variation, and review the recent progress in the detection and mapping of loci and the cloning of large-effect genes.

Natural allelic variation identifies new genes in the Arabidopsis circadian system

We have analysed the circadian rhythm of Arabidopsis thaliana leaf movements in the accession Cvi from the Cape Verde Islands, and in the commonly used laboratory strains Columbia (Col) and Landsberg (erecta) (Ler), which originated in Northern Europe. The parental lines have similar rhythmic periods, but the progeny of crosses among them reveal extensive variation for this trait. An analysis of 48 Ler/Cvi recombinant inbred lines (RILs) and a further 30 Ler/Col RILs allowed us to locate four putative quantitative trait loci (QTLs) that control the period of the circadian clock. Near-isogenic lines (NILs) that contain a QTL in a small, defined chromo- somal region allowed us to confirm the phenotypic effect and to map the positions of three period QTLs, designated ESPRESSO, NON TROPPO and RALENTANDO. Quantitative trait loci at the locations of RALENTANDO and of a fourth QTL, ANDANTE, were identified in both Ler/Cvi and Ler/Col RIL populations. Some QTLs for circadian period are closely linked to loci that control flowering time, including FLC. We show that flc mutations shorten the circadian period such that the known allelic variation in the MADS-box gene FLC can account for the ANDANTE QTL. The QTLs ESPRESSO and RALENTANDO identify new genes that regulate the Arabidopsis circadian system in nature, one of which may be the flowering-time gene GIGANTEA.

Natural allelic variation at seed size loci in relation to other life history traits of Arabidopsis thaliana

We have analyzed two Arabidopsis strains differing in the mean seed size and seed number they produced. The accession Cape Verde Islands (Cvi) yielded on average about 40% fewer seeds than the laboratory strain Landsberg erecta (Ler), but Cvi seeds were almost twice as heavy. Maternal and nonmaternal genetic factors were involved in the seed size variation, and interactions between both types of factors presumably occurred. The Ler/Cvi seed size difference increased through seed development from ovule maturation until seed desiccation, suggesting that multiple processes of seed development were affected. In addition, it involved changes in the final cell number and cell size of the seed coat and the embryo. Cell number variation was controlled mainly by maternal factors, whereas nonmaternal allelic variation mostly affected cell size. By using a recombinant inbred line population derived from Ler and Cvi, we mapped quantitative trait loci (QTLs) affecting 12 life history traits related to seed size, fruit size, seed number, and plant resources. Five of the seed size QTLs colocated with QTLs for other traits, suggesting that they control seed size via maternal components affecting ovule number and/or carpel development, ovule development, or reproductive resource allocation in the mother plant. The six remaining putative seed size QTLs did not show a significant effect on any other trait, suggesting that this allelic variation may be involved specifically in seed development processes.

Analysis of natural allelic variation at flowering time loci in the Landsberg erecta and Cape Verde Islands ecotypes of Arabidopsis thaliana

We have analyzed the flowering behavior of two Arabidopsis ecotypes: the laboratory strain Landsberg erecta (Ler) and an ecotype from the tropical Cape Verde Islands (Cvi). They differ little in their flowering phenotypes and in their responses to photoperiod length changes and to vernalization treatment. However, segregating populations derived from crosses between them showed a much larger variation. An approach of quantitative trait locus (QTL) mapping in recombinant inbred lines (RILs) grown under three environments differing in day-length and/or vernalization treatment has been used to detect and locate flowering loci. Four main QTLs were identified, designated early day-length insensitive (EDI), flowering F, G, and H (FLF, FLG, and FLH, respectively), to which most of the flowering behavior differences could be attributed. To further characterize the individual loci, near isogenic lines were constructed by introgressing Cvi early alleles of EDI and FLH into the Ler genetic background. EDI-Cvi alleles produce earliness under both long- and short-day photoperiods, rendering Ler plants almost day-length neutral. In addition, RILs were selected to analyze FLF and FLG. These loci interact epistatically and RILs carrying late alleles at FLF and FLG were very responsive to vernalization and showed an increased response to photoperiod length changes. The possible role of these loci for the control of flowering is discussed in the context of the current Arabidopsis model.

Development of an AFLP based linkage map of Ler, Col and Cvi Arabidopsis thaliana ecotypes and construction of a Ler/Cvi recombinant inbred line population

An amplified fragment polymorphism (AFLP) based linkage map has been generated for a new Landsberg erecta/ Cape Verde Islands (Ler/Cvi) recombinant inbred line (RIL) population. A total of 321 molecular PCR based markers and the erecta mutation were mapped. AFLP markers were also analysed in the Landsberg erecta/Columbia (Ler/Col) RIL population (Lister and Dean, 1993) and 395 AFLP markers have been integrated into the previous Arabidopsis molecular map of 122 RFLPs, CAPSs and SSLPs. This enabled the evaluation of the efficiency and robustness of AFLP technology for linkage analyses in Arabidopsis. AFLP markers were found throughout the linkage map. The two RIL maps could be integrated through 49 common markers which all mapped at similar positions. Comparison of both maps led to the conclusion that segregating bands from a common parent can be compared between different populations, and that AFLP bands of similar molecular size, amplified with the same primer combination in two different ecotypes, are likely to correspond to the same locus. AFLPs were found clustering around the centromeric regions, and the authors have established the map position of the centromere of chromosome 3 by a quantitative analysis of AFLP bands using trisomic plants. AFLP markers were also used to estimate the polymorphism rate among the three ecotypes. The larger polymorphism rate found between Ler and Cvi compared to Ler and Col will mean that the new RIL population will provide a useful material to map DNA polymorphisms and quantitative trait loci.

Cytogenetics for the model system Arabidopsis thaliana

A detailed karyotype of Arabidopsis thaliana is presented using meiotic pachytene cells in combination with fluorescence in situ hybridization. The lengths of the five pachytene bivalents varied between 50 and 80 microns, which is 20-25 times longer than mitotic metaphase chromosomes. The analysis confirms that the two longest chromosomes (1 and 5) are metacentric and the two shortest chromosomes (2 and 4) are acrocentric and carry NORs subterminally in their short arms, while chromosome 3 is submetacentric and medium sized. Detailed mapping of the centromere position further revealed that the length variation between the pachytene bivalents comes from the short arms. Individual chromosomes were unambiguously identified by their combinations of relative lengths, arm-ratios, presence of NOR knobs and FISH signals with a 5S rDNA probe and chromosome specific DNA probes. Polymorphisms were found among six ecotypes with respect to the number and map positions of 5S rDNA loci. All ecotypes contain 5S rDNA in the short arms of chromosomes 4 and 5. Three different patterns were observed regarding the presence and position of a 5S rDNA locus on chromosome 3. Repetitive DNA clones enabled us to subdivide the pericentromeric heterochromatin into a central domain, characterized by pAL1 and 106B repeats, which accommodate the functional centromere and two flanking domains, characterized by the 17 A20 repeat sequences. The upper flanking domains of chromosomes 4 and 5, and in some ecotypes also chromosome 3, contain a 5S rDNA locus. The detection of unique cosmids and YAC sequences demonstrates that detailed physical mapping of Arabidopsis chromosomes by cytogenetic techniques is feasible. Together with the presented karyotype this makes Arabidopsis a model system for detailed cytogenetic mapping.

Genetic interactions among late-flowering mutants of Arabidopsis

Flowering time in Arabidopsis is controlled by a large number of genes, identified by induced mutations. Forty-two double mutants involving 10 of these loci were obtained and analyzed for their flowering behavior under long-day conditions, with and without vernalization, and under short-day conditions. The genetic interactions between the various mutants proved to be complex, although a major epistatic group (called group A) could be identified corresponding to the mutants, which are relatively insensitive to vernalization and daylength. In contrast, the genetic behavior of the mutants much more responsive to these environmental factors (group B) is more complex. The vernalization responsiveness of the group B mutants did not compensate for the lateness of the group A mutants. This indicated that these genes do not control vernalization sensitivity as such, but provide a factor that becomes limiting in short days. The classification of these mutants in different physiological groups is discussed in relation to the detected genetic interactions, and based on these interactions a more detailed model of their role in flowering initiation is proposed.