RESUMEN
Long days (LD) promote flowering of Arabidopsis thaliana compared with short days (SD) by activating the photoperiodic pathway. Here we show that growth under very-SD (3â h) or darkness (on sucrose) also accelerates flowering on a biological scale, indicating that SD actively repress flowering compared with very-SD. CONSTANS (CO) repressed flowering under SD, and the early flowering of co under SD required FLOWERING LOCUS T (FT). FT was expressed at a basal level in the leaves under SD, but these levels were not enhanced in co. This indicates that the action of CO in A. thaliana is not the mirror image of the action of its homologue in rice. In the apex, CO enhanced the expression of TERMINAL FLOWER 1 (TFL1) around the time when FT expression is important to promote flowering. Under SD, the tfl1 mutation was epistatic to co and in turn ft was epistatic to tfl1. These observations are consistent with the long-standing but not demonstrated model where CO can inhibit FT induction of flowering by affecting TFL1 expression.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas de Unión al ADN/metabolismo , Regulación de la Expresión Génica de las Plantas , Factores de Transcripción/metabolismo , Arabidopsis/fisiología , Proteínas de Arabidopsis/genética , Proteínas de Unión al ADN/genética , Flores/genética , Flores/fisiología , Fotoperiodo , Factores de Transcripción/genéticaRESUMEN
Long days repeatedly enhance the expression of the FLOWERING LOCUS T (FT) gene during the evening and early night. This signal induces flowering despite low FT expression the rest of the day. To investigate whether this temporal behaviour transmits information, plants of Arabidopsis thaliana were exposed to different day-night cycles, including combinations that induced FT expression out of normal hours. Flowering time best correlated with the integral of FT expression over several days, corrected for a higher evening and early night sensitivity to FT. We generated a system to induce FT expression in a leaf removed 8-12 h later. The expression of flowering genes in the apex and flowering required cycles of induction repeated over several days. Evening and early night FT induction was the most effective. The temporal pattern of FT expression encodes information that discriminates long days from other inputs.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/fisiología , Flores/fisiología , Regulación de la Expresión Génica de las Plantas , Proteínas de Arabidopsis/metabolismo , Ritmo Circadiano/genética , Flores/genética , Meristema/genética , Fotoperiodo , Plantas Modificadas GenéticamenteRESUMEN
Phytochrome A (phyA) is crucial to initiate the early steps of the transition between skoto- and photomorphogenesis upon light exposure and to complete this process under far-red light (typical of dense vegetation canopies). However, under prolonged red or white light, phyA mutants are hyper-photomorphogenic in many respects. To investigate this issue, we analyzed the late response of the transcriptome of the phyA mutant to red light. Compared to the wild-type (WT), hyper-responsive genes outnumbered the genes showing reduced response to red light in phyA. A network analysis revealed the co-expression of PHYTOCHROME INTERACTING FACTOR 1 (PIF1) with those genes showing hyper-promotion by red light in phyA. The enhanced responses of gene expression, cotyledon unfolding, hypocotyl growth, and greening observed in the phyA mutant compared to the WT were absent in the phyA pif1 double mutant compared to pif1, indicating that the hyper-photomorphogenic phenotype of phyA requires PIF1. PIF1 directly binds to gene promoters that displayed PIF1-mediated enhanced response to red light. Expression of mutant PIF1 deficient in interactions with phyA and phyB enhanced the long-term growth response to red light but reduced the expression of selected genes in response to red light. We propose that phytochrome-mediated degradation of PIF1 prevents over-activation of photomorphogenesis during early seedling development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Luz , Fitocromo A/metabolismo , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/química , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/química , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Mutación , Fitocromo A/genética , Fitocromo B/metabolismo , Estabilidad Proteica/efectos de la radiación , Estructura Terciaria de Proteína , Proteolisis/efectos de la radiación , Plantones/crecimiento & desarrollo , Plantones/efectos de la radiaciónRESUMEN
The vasopressin peptide analog desmopressin has been used during surgery to prevent bleeding in patients with coagulation defects. Recent experimental and clinical data revealed that perioperative desmopressin therapy can minimize the spread and survival of residual cancer cells. Here, we explored the antitumor effects of desmopressin in combination with chemotherapeutic agents using the F3II mammary carcinoma in syngeneic Balb/c mice. Intravenous administration of desmopressin at a dose of 2 microg/kg together with weekly cycles of carmustine (20 mg/kg) prevented primary tumor infiltration of the skin. Combination of desmopressin with paclitaxel (25 mg/kg) significantly reduced metastatic progression to the lung. Although desmopressin had an antiproliferative effect on F3II cells, in vitro studies did not demonstrate an enhanced cytotoxicity with chemotherapy. Our results suggest that desmopressin may contribute to impair aggressiveness of residual mammary tumors during chemotherapy.