Quantification of Xylem-Specific Thermospermine-Dependent Translation of SACL Transcripts with Dual Luciferase Reporter System.

Thermospermine (Tspm) is a polyamine found to play a crucial role in xylem development in Arabidopsis thaliana. Tspm promotes the translation of the SACL genes by counteracting the activity of a cis element in their 5'-leader region that suppresses the translation of the main ORF. Here we describe a method to test the Tspm-dependent translational regulation of the 5'-leader of the SACL mRNAs in Nicotiana benthamiana leaves and A. thaliana mesophyll protoplasts with a dual luciferase assay. The dual luciferase reporter system is used to assess gene expression and is based on the detection of the Firefly luciferase luminescence driven by a specific promoter. However, it can also be used to evaluate the cis elements found in 5'-leader that influence the translation of the main ORF in a transcript. We have used a modified version of the pGreenII 0800 LUC plasmid carrying a double 35S promoter, followed by a poly-linker sequence in phase with the Firefly luciferase gene (pGreen2x35SLUC) where the full 5'-leader sequence of SACL3 was cloned. This construct was used for Agrobacterium tumefaciens infiltration of N. benthamiana leaves and for transfection of A. thaliana mesophyll protoplasts, followed by mock or Tspm treatments. The resulting translation of the Firefly luciferase in these organisms and conditions was then tested by measuring luminescence with the dual luciferase assay and a luminometer. These experiments have allowed us to quantify the positive effect of Tspm in the translation of SACL3 transcripts.

Residence, Clinical Features, and Genetic Risk Factors Associated with Symptoms of COVID-19 in a Cohort of Older People in Madrid.

BACKGROUND: The older population has been especially affected by the severe acute respiratory syndrome coronavirus 2 pandemic (COVID-19). OBJECTIVE: The aim of the study was to explore the incidence, severity, mortality rate, clinical features, and risk factors of symptoms of COVID-19 in home-dwelling older people, and its association with type of residence, cognitive deterioration, and neurodegenerative diseases. METHODS: Data about symptoms of COVID-19 were collected through a telephone survey in the cohort of 913 older volunteers of the Vallecas Project, aged 75-90 years, most of them (902) home-dwelling, in Madrid, Spain. The association of demographic and anthropometric measures, genetic polymorphisms, comorbidities, life habits, type of residence, and frailty surrogates were explored as potential risk factors for the incidence, severity, and mortality of COVID-19 in the older population. FINDINGS: Sixty-two cases reported symptoms compatible with COVID-19; 6 of them had died, 4 in their home and 2 in the nursing home. Moderate/severe cases were significantly older and more frequently males. The APOE ε4 allele was associated with the presence of symptoms of COVID-19. Higher systolic blood pressure, more intense smoking habit, more alcohol intake, lower consumption of coffee and tea, and cognitive impairment were associated with disease severity. CONCLUSIONS: The estimated incidence of symptomatic COVID-19 in this older cohort of Madrid was 6.8%, with an overall mortality rate of 0.7% (18.2% in those living in a nursing home) and a fatality rate of 9.9%. Our exploratory study indicates that life habits, other clinical conditions and, the ε4 variant of the APOE gene are associated with the presence and clinical severity of coronavirus infection.

COP1 destabilizes DELLA proteins in Arabidopsis.

DELLA transcriptional regulators are central components in the control of plant growth responses to the environment. This control is considered to be mediated by changes in the metabolism of the hormones gibberellins (GAs), which promote the degradation of DELLAs. However, here we show that warm temperature or shade reduced the stability of a GA-insensitive DELLA allele in Arabidopsis thaliana Furthermore, the degradation of DELLA induced by the warmth preceded changes in GA levels and depended on the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1). COP1 enhanced the degradation of normal and GA-insensitive DELLA alleles when coexpressed in Nicotiana benthamiana. DELLA proteins physically interacted with COP1 in yeast, mammalian, and plant cells. This interaction was enhanced by the COP1 complex partner SUPRESSOR OF phyA-105 1 (SPA1). The level of ubiquitination of DELLA was enhanced by COP1 and COP1 ubiquitinated DELLA proteins in vitro. We propose that DELLAs are destabilized not only by the canonical GA-dependent pathway but also by COP1 and that this control is relevant for growth responses to shade and warm temperature.

The MPK8-TCP14 pathway promotes seed germination in Arabidopsis.

The accurate control of dormancy release and germination is critical for successful plantlet establishment. Investigations in cereals hypothesized a crucial role for specific MAP kinase (MPK) pathways in promoting dormancy release, although the identity of the MPK involved and the downstream events remain unclear. In this work, we characterized mutants for Arabidopsis thaliana MAP kinase 8 (MPK8). Mpk8 seeds presented a deeper dormancy than wild-type (WT) at harvest that was less efficiently alleviated by after-ripening and gibberellic acid treatment. We identified Teosinte Branched1/Cycloidea/Proliferating cell factor 14 (TCP14), a transcription factor regulating germination, as a partner of MPK8. Mpk8 tcp14 double-mutant seeds presented a deeper dormancy at harvest than WT and mpk8, but similar to that of tcp14 seeds. MPK8 interacted with TCP14 in the nucleus in vivo and phosphorylated TCP14 in vitro. Furthermore, MPK8 enhanced TCP14 transcriptional activity when co-expressed in tobacco leaves. Nevertheless, the stimulation of TCP14 transcriptional activity by MPK8 could occur independently of TCP14 phosphorylation. The comparison of WT, mpk8 and tcp14 transcriptomes evidenced that whereas no effect was observed in dry seeds, mpk8 and tcp14 mutants presented dramatic transcriptomic alterations after imbibition with a sustained expression of genes related to seed maturation. Moreover, both mutants exhibited repression of genes involved in cell wall remodeling and cell cycle G1/S transition. As a whole, this study unraveled a role for MPK8 in promoting seed germination, and suggested that its interaction with TCP14 was critical for regulating key processes required for germination completion.

Effects of commonly prescribed drugs on cognition and mild cognitive impairment in healthy elderly people.

BACKGROUND: Chronic drug intake has been associated with negative and positive cognitive effects in elderly people, although subjacent conditions may be confounding factors. AIM: To study the effects on cognitive performance of commonly prescribed medications in a cohort of cognitively normal older adults. METHODS: Medication intake was recorded during two years in 1087 individuals 70-85 years old, without neurological or psychiatric conditions. The influence of every drug, drug family and therapeutic group on six cognitive scores and on the conversion to mild cognitive impairment over two years was ascertained by cross-sectional and longitudinal analyses controlling for demographic and clinical variables. RESULTS: Small effects of several drugs on information processing were found in cross-sectional analyses but only confirmed for a positive effect of vitamin D in case-control analyses. Longitudinal analyses showed no drug effects on the cognitive slopes. Several hypotensive drugs reduced, whereas bromazepam and glucose lowering drugs increased, the conversion rate to mild cognitive impairment with very small effects (R2=0.3-1%). CONCLUSIONS: Cognitively healthy elderly individuals show minimal negative effects on information processing associated with chronic intake of some drugs probably related to the subjacent condition. Some drugs slightly affect the rate of conversion to mild cognitive impairment. Positive effects of vitamin D, chondroitin, atorvastatin and antihypertensive drugs, and negative effects of antidepressants and benzodiazepines, should be further explored in studies with longer follow-up.

The transcriptional regulator BBX24 impairs DELLA activity to promote shade avoidance in Arabidopsis thaliana.

In response to canopy shade, plant vegetative structures elongate to gain access to light. However, the mechanism that allows a plastic transcriptional response to canopy shade light is not fully elucidated. Here we propose that the activity of PIF4, a key transcription factor in the shade signalling network, is modulated by the interplay between the BBX24 transcriptional regulator and DELLA proteins, which are negative regulators of the gibberellin (GA) signalling pathway. We show that GA-related targets are enriched among genes responsive to BBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GA treatment that promotes DELLA degradation. BBX24 physically interacts with DELLA proteins and alleviates DELLA-mediated repression of PIF4 activity. The proposed molecular mechanism provides reversible regulation of the activity of a key transcription factor that may prove especially relevant under fluctuating light conditions.

Large-scale identification of gibberellin-related transcription factors defines group VII ETHYLENE RESPONSE FACTORS as functional DELLA partners.

DELLA proteins are the master negative regulators in gibberellin (GA) signaling acting in the nucleus as transcriptional regulators. The current view of DELLA action indicates that their activity relies on the physical interaction with transcription factors (TFs). Therefore, the identification of TFs through which DELLAs regulate GA responses is key to understanding these responses from a mechanistic point of view. Here, we have determined the TF interactome of the Arabidopsis (Arabidopsis thaliana) DELLA protein GIBBERELLIN INSENSITIVE and screened a collection of conditional TF overexpressors in search of those that alter GA sensitivity. As a result, we have found RELATED TO APETALA2.3, an ethylene-induced TF belonging to the group VII ETHYLENE RESPONSE FACTOR of the APETALA2/ethylene responsive element binding protein superfamily, as a DELLA interactor with physiological relevance in the context of apical hook development. The combination of transactivation assays and chromatin immunoprecipitation indicates that the interaction with GIBBERELLIN INSENSITIVE impairs the activity of RELATED TO APETALA2.3 on the target promoters. This mechanism represents a unique node in the cross regulation between the GA and ethylene signaling pathways controlling differential growth during apical hook development.

Dynamic regulation of cortical microtubule organization through prefoldin-DELLA interaction.

Plant morphogenesis relies on specific patterns of cell division and expansion. It is well established that cortical microtubules influence the direction of cell expansion, but less is known about the molecular mechanisms that regulate microtubule arrangement. Here we show that the phytohormones gibberellins (GAs) regulate microtubule orientation through physical interaction between the nuclear-localized DELLA proteins and the prefoldin complex, a cochaperone required for tubulin folding. In the presence of GA, DELLA proteins are degraded, and the prefoldin complex stays in the cytoplasm and is functional. In the absence of GA, the prefoldin complex is localized to the nucleus, which severely compromises α/ß-tubulin heterodimer availability, affecting microtubule organization. The physiological relevance of this molecular mechanism was confirmed by the observation that the daily rhythm of plant growth was accompanied by coordinated oscillation of DELLA accumulation, prefoldin subcellular localization, and cortical microtubule reorientation.

Role of polyamines in plant vascular development.

Several pieces of evidence suggest a role for polyamines in the regulation of plant vascular development. For instance, polyamine oxidase gene expression has been shown to be associated with lignification, and downregulation of S-adenosylmethionine decarboxylase causes dwarfism and enlargement of the vasculature. Recent evidence from Arabidopsis thaliana also suggests that the active polyamine in the regulation of vascular development is the tetraamine thermospermine. Thermospermine biosynthesis is catalyzed by the aminopropyl transferase encoded by ACAULIS5, which is specifically expressed in xylem vessel elements. Both genetic and molecular evidence support a fundamental role for thermospermine in preventing premature maturation and death of the xylem vessel elements. This safeguard action of thermospermine has significant impact on xylem cell morphology, cell wall patterning and cell death as well as on plant growth in general. This manuscript reviews recent reports on polyamine function and places polyamines in the context of the known regulatory mechanisms that govern vascular development.

A polyamine metabolon involving aminopropyl transferase complexes in Arabidopsis.

The conversion of putrescine to spermidine in the biosynthetic pathway of plant polyamines is catalyzed by two closely related spermidine synthases, SPDS1 and SPDS2, in Arabidopsis. In the yeast two-hybrid system, SPDS2 was found to interact with SPDS1 and a novel protein, SPMS (spermine synthase), which is homologous with SPDS2 and SPDS1. SPMS interacts with both SPDS1 and SPDS2 in yeast and in vitro. Unlike SPDS1 and SPDS2, SPMS failed to suppress the speDelta3 deficiency of spermidine synthase in yeast. However, SPMS was able to complement the speDelta4 spermine deficiency in yeast, indicating that SPMS is a novel spermine synthase. The SPDS and SPMS proteins showed no homodimerization but formed heterodimers in vitro. Pairwise coexpression of hemagglutinin- and c-Myc epitope-labeled proteins in Arabidopsis cells confirmed the existence of coimmunoprecipitating SPDS1-SPDS2 and SDPS2-SPMS heterodimers in vivo. The epitope-labeled SPDS and SPMS proteins copurified with protein complexes ranging in size from 650 to 750 kD. Our data demonstrate the existence of a metabolon involving at least the last two steps of polyamine biosynthesis in Arabidopsis.