Leaves and flowers begin life as outgrowths from the edges of shoot apical meristems. Stem cell divisions in the meristem center replenish cells that are incorporated into organ primordia at the ...meristem periphery and leave the meristem. Organ boundaries, regions of limited growth that separate forming organs from the meristem, serve to isolate these two domains and are critical for coordination of organogenesis and meristem maintenance. Boundary formation and maintenance are poorly understood processes, despite the identification of a number of boundary-specific transcription factors. Here we provide genetic and biochemical evidence that the Arabidopsis thaliana transcription factor LATERAL ORGAN BOUNDARIES (LOB) negatively regulates accumulation of the plant steroid hormone brassinosteroid (BR) in organ boundaries. We found that ectopic expression of LOB results in reduced BR responses. We identified BAS1 , which encodes a BR-inactivating enzyme, as a direct target of LOB transcriptional activation. Loss-of-function lob mutants exhibit organ fusions, and this phenotype is suppressed by expression of BAS1 under the LOB promoter, indicating that BR hyperaccumulation contributes to the lob mutant phenotype. In addition, LOB expression is BR regulated; therefore, LOB and BR form a feedback loop to modulate local BR accumulation in organ boundaries to limit growth in the boundary domain.
Upon detecting abiotic or biotic stress, plants generally reduce their growth, enabling resources to be conserved and diverted to stress response mechanisms. In Arabidopsis thaliana, the AT-hook ...motif nuclear-localized (AHL) transcription factor family has been implicated in restricting rosette growth in response to stress. However, the mechanism by which AHLs repress growth in rosettes is unknown. In this study, we establish that SUPPRESSOR OF PHYTOCHROME B4-#3 (SOB3) and other AHLs restrict petiole elongation by antagonizing the growth-promoting PHYTOCHROME-INTERACTING FACTORs (PIFs). Our data show that high levels of SOB3 expression lead to a short-petiole phenotype similar to that conferred by removal of PIF4. Conversely, the dominant-negative sob3-6 mutant has long petioles, a phenotype which is PIF-dependent. We further show that AHLs repress the expression of many PIF-activated genes, several of which are involved in hormone-mediated promotion of growth. Additionally, a subset of PIF-activated, AHL-repressed genes are directly bound by both SOB3 and PIFs. Finally, SOB3 reduces binding of PIF4 to shared target loci. Collectively, our results demonstrate that AHLs repress petiole growth by antagonizing PIF-mediated transcriptional activation of genes associated with growth and hormone pathways. By elucidating a mechanism via which the stress-responsive AHL transcription factor family influences growth in petioles, this study identifies a key step in the gene regulatory network controlling leaf growth in response to the environment.
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•AHL transcription factors repress petiole elongation in juvenile rosettes•The effect of AHLs on petiole growth is dependent on PIFs•AHLs bind to and repress the expression of genes directly activated by PIFs•PIF binding to target genes is reduced by ectopic AHL expression
Favero et al. demonstrate that the AHL transcription factors repress leaf petiole elongation by antagonizing key regulators of plant growth, the PIFs. AHLs bind to PIF-targeted loci and reduce PIF binding to these regions, thus inhibiting transcriptional activation of growth-promoting genes.
Heterostyly is a breeding system that promotes outbreeding through a combination of morphological and physiological floral traits. In Turnera these traits are governed by a single, hemizygous S-locus ...containing just three genes. We report that the S-locus gene, BAHD, is mutated and encodes a severely truncated protein in a self-compatible long homostyle species. Further, a self-compatible long homostyle mutant possesses a T. krapovickasii BAHD allele with a point mutation in a highly conserved domain of BAHD acyl transferases. Wild type and mutant TkBAHD alleles were expressed in Arabidopsis to assay for brassinosteroid (BR) inactivating activity. The wild type but not mutant allele caused dwarfism, consistent with the wild type possessing, but the mutant allele having lost, BR inactivating activity. To investigate whether BRs act directly in self-incompatibility, BRs were added to in vitro pollen cultures of the two mating types. A small morph specific stimulatory effect on pollen tube growth was found with 5 µM brassinolide, but no genotype specific inhibition was observed. These results suggest that BAHD acts pleiotropically to mediate pistil length and physiological mating type through BR inactivation, and that in regard to self-incompatibility, BR acts by differentially regulating gene expression in pistils, rather than directly on pollen.
The 29-member Arabidopsis AHL gene family is classified into three main classes based on nucleotide and protein sequence evolutionary differences. These differences include the presence or absence of ...introns, type and/or number of conserved AT-hook and PPC domains. AHL gene family members are divided into two phylogenetic clades, Clade-A and Clade-B. A majority of the 29 members remain functionally uncharacterized. Furthermore, the biological significance of the DNA and peptide sequence diversity, observed in the conserved motifs and domains found in the different AHL types, is a subject area that remains largely unexplored.
Transgenic plants overexpressing AtAHL20 flowered later than the wild type under both short and long days. Transcript accumulation analyses showed that 35S:AtAHL20 plants contained reduced FT, TSF, AGL8 and SPL3 mRNA levels. Similarly, overexpression of AtAHL20's orthologue in Camelina sativa, Arabidopsis' closely related Brassicaceae family member species, conferred a late-flowering phenotype via suppression of CsFT expression. However, overexpression of an aberrant AtAHL20 gene harboring a missense mutation in the AT-hook domain's highly conserved R-G-R core motif abolished the late-flowering phenotype. Data from targeted yeast-two-hybrid assays showed that AtAHL20 interacted with itself and several other Clade-A Type-I AHLs which have been previously implicated in flowering-time regulation: AtAHL19, AtAHL22 and AtAHL29.
We showed via gain-of-function analysis that AtAHL20 is a negative regulator of FT expression, as well as other downstream flowering time regulating genes. A similar outcome in Camelina sativa transgenic plants overexpressing CsAHL20 suggest that this is a conserved function. Our results demonstrate that AtAHL20 acts as a photoperiod-independent negative regulator of transition to flowering.
Background: Epidemiologic data have shown that obesity independently increases colorectal cancer (CRC) risk, but the mechanisms are poorly understood. Obesity is an inflammatory state, and chronic ...colonic inflammation induces CRC.
Objective: We conducted this proof-of-principle study to seek evidence of obesity-associated colorectal inflammation and to evaluate effects of diet-induced weight loss.
Design: We measured inflammatory cytokines, gene arrays, and macrophage infiltration in rectosigmoid mucosal biopsies of 10 obese premenopausal women mean ± SD body mass index (in kg/m2): 35 ± 3.5 before and after weight loss induced by a very-low-calorie diet.
Results: Subjects lost a mean (±SD) of 10.1 ± 1% of their initial weight. Weight loss significantly reduced fasting blood glucose, total cholesterol, triglycerides, LDL, tumor necrosis factor-α (TNF-α), and interleukin (IL)-8 concentrations (P < 0.05). After weight loss, rectosigmoid biopsies showed a 25–57% reduction in TNF-α, IL-1β, IL-8, and monocyte chemotactic protein 1 concentrations (P < 0.05). T cell and macrophage counts decreased by 28% and 42%, respectively (P < 0.05). Gene arrays showed dramatic down-regulation of proinflammatory cytokine and chemokine pathways, prostaglandin metabolism, and the transcription factors STAT3 (signal transducer and activator of transcription 3) and nuclear transcription factor κB. Weight loss reduced expression of FOS and JUN genes and down-regulated oxidative stress pathways and the transcription factors ATF (activating transcription factor) and CREB (cyclic AMP response element-binding).
Conclusions: Our data show that diet-induced weight loss in obese individuals reduces colorectal inflammation and greatly modulates inflammatory and cancer-related gene pathways. These data imply that obesity is accompanied by inflammation in the colorectal mucosa and that diet-induced weight loss reduces this inflammatory state and may thereby lower CRC risk.
Purpose
Physical activity studies involving bariatric surgery patients tend to be short-term or cross-sectional investigations. Longer-term studies are limited and typically consist of relatively ...brief objective measurement periods used to generalize activity patterns. Very little research combines objective measurements with structured interviews to determine both the patterns and related factors of long-term physical activity among patients undergoing bariatric surgery.
Materials and Methods
Previous volunteers in a perioperative physical activity study were invited to participate in a mixed methods study investigating physical activity among bariatric patients over a 5-year postoperative period. Fifty-one patients (
M
age
= 45.4 years; 76.5% female, 90.2% White; 86.3% Roux-en-Y procedure) provided interview, survey, accelerometer, and anthropometric data.
Results
Participants were divided into four exercise quartiles, based on self-report of their length of regular exercise involvement from 1 year before through 5 years after surgery. Those reporting the most periods of regular exercise took the most measured steps per day, had greater moderate-to-vigorous physical activity and more bout-related activity, experienced the largest decrease in BMI, and reported the most adherence to nutritional guidelines. Participants reporting the most and least physical activity found the measurement periods to be most similar to their normal activity patterns. While physical activity increased significantly after surgery, measured physical activity did not reach recommended levels for steps or exercise bout minutes.
Conclusions
Measured physical activity and self-reported physical activity show congruent trends among patients undergoing bariatric surgery. More research is needed to determine optimal long-term monitoring and promotion of physical activity among patients.
Graphical Abstract
Single, double, and triple null combinations of Arabidopsis mutants lacking the photoreceptors phytochrome (phy) A (phyA-201), phyB (phyB-5), and cryptochrome (cry) 1 (hy4-2.23n) were examined for ...de-etiolation responses in high-fluence red, far-red, blue, and broad-spectrum white light. Cotyledon unhooking, unfolding, and expansion, hypocotyl growth, and the accumulation of chlorophylls and anthocyanin in 5-d-old seedlings were measured under each light condition and in the dark. phyA was the major photoreceptor/effector for most far-red-light responses, although phyB and cry1 modulated anthocyanin accumulation in a phyA-dependent manner. phyB was the major photoreceptor in red light, although cry1 acted as a phyA/phyB-dependent modulator of chlorophyll accumulation under these conditions. All three photoreceptors contributed to most blue light deetiolation responses, either redundantly or additively; however, phyB acted as a modulator of cotyledon expansion dependent on the presence of cry1. As reported previously, flowering time in long days was promoted by phyA and inhibited by phyB, with each suppressing the other's effect. In addition to the effector/modulator relationships described above, measurements of hypocotyls from blue-light-grown seedlings demonstrated phytochrome activity in blue light and cry1 activity in a phyAphyB mutant background
SUPPRESSOR OF PHYTOCHROME B-4 #3 (SOB3) is a member of the AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED (AHL) family of transcription factors that are involved in light-mediated growth in Arabidopsis ...thaliana, affecting processes such as hypocotyl elongation. The majority of the research on the AHLs has been conducted in continuous light. However, there are unique molecular events that promote growth in short days (SD) compared to constant light conditions. Therefore, we investigated how AHLs affect hypocotyl elongation in SD. Firstly, we observed that AHLs inhibit hypocotyl growth in SD, similar to their effect in constant light. Next, we identified AHL-regulated genes in SD-grown seedlings by performing RNA-seq in two sob3 mutants at different time points. Our transcriptomic data indicate that PHYTOCHROME INTERACTING FACTORS (PIFs) 4, 5, 7, and 8 along with PIF-target genes are repressed by SOB3 and/or other AHLs. We also identified PIF target genes that are repressed and have not been previously described as AHL-regulated, including PRE1, PIL1, HFR1, CDF5, and XTR7. Interestingly, our RNA-seq data also suggest that AHLs activate the expression of growth repressors to control hypocotyl elongation, such as HY5 and IAA17. Notably, many growth-regulating and other genes identified from the RNA-seq experiment were differentially regulated between these two sob3 mutants at the time points tested. Surprisingly, our ChIP-seq data suggest that SOB3 mostly binds to similar genes throughout the day. Collectively, these data suggest that AHLs affect gene expression in a time point-specific manner irrespective of changes in binding to DNA throughout SD.
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