Characterization of Root Epidermal Cell Patterning and Differentiation in Arabidopsis.

The root epidermis of Arabidopsis thaliana has been established as a model system for elucidating the mechanisms which govern the spatial patterningAbstract and morphogenesis of plant cells. Investigations into root hairs focus on various aspects of the biology of epidermal cells, using methods specifically developed to dissect the biological question under study. Despite the large number of studies related to epidermal cell differentiation, a survey of methods to analyze the phenotypic readout resulting from environmental conditions or the genetic background of the plant has not been provided so far. This protocol describes how to analyze the spatial arrangement and morphologic characteristics of cells in the root epidermis based on whole mount roots or cross sections, using confocal, scanning electron and light microscopy. This comparison of methods aids in selecting the most suitable strategy to examine the differentiation of root epidermal cells at different developmental stages.

BES1 regulates the localization of the brassinosteroid receptor BRL3 within the provascular tissue of the Arabidopsis primary root.

Brassinosteroid (BR) hormones are important regulators of plant growth and development. Recent studies revealed the cell-specific role of BRs in vascular and stem cell development by the action of cell-specific BR receptor complexes and downstream signaling components in Arabidopsis thaliana Despite the importance of spatiotemporal regulation of hormone signaling in the control of plant vascular development, the mechanisms that confer cellular specificity to BR receptors within the vascular cells are not yet understood. The present work shows that BRI1-like receptor genes 1 and 3 (BRL1 and BRL3) are differently regulated by BRs. By using promoter deletion constructs of BRL1 and BRL3 fused to GFP/GUS (green fluorescent protein/ß-glucuronidase) reporters in Arabidopsis, analysis of their cell-specific expression and regulation by BRs in the root apex has been carried out. We found that BRL3 expression is finely modulated by BRs in different root cell types, whereas the location of BRL1 appears to be independent of this hormone. Physiological and genetic analysis show a BR-dependent expression of BRL3 in the root meristem. In particular, BRL3 expression requires active BES1, a central transcriptional effector within the BRI1 pathway. ChIP analysis showed that BES1 directly binds to the BRRE present in the BRL3 promoter region, modulating its transcription in different subsets of cells of the root apex. Overall our study reveals the existence of a cell-specific negative feedback loop from BRI1-mediated BES1 transcription factor to BRL3 in phloem cells, while contributing to a general understanding of the spatial control of steroid signaling in plant development.

The regulation and plasticity of root hair patterning and morphogenesis.

Root hairs are highly specialized cells found in the epidermis of plant roots that play a key role in providing the plant with water and mineral nutrients. Root hairs have been used as a model system for understanding both cell fate determination and the morphogenetic plasticity of cell differentiation. Indeed, many studies have shown that the fate of root epidermal cells, which differentiate into either root hair or non-hair cells, is determined by a complex interplay of intrinsic and extrinsic cues that results in a predictable but highly plastic pattern of epidermal cells that can vary in shape, size and function. Here, we review these studies and discuss recent evidence suggesting that environmental information can be integrated at multiple points in the root hair morphogenetic pathway and affects multifaceted processes at the chromatin, transcriptional and post-transcriptional levels.

Discriminative gene co-expression network analysis uncovers novel modules involved in the formation of phosphate deficiency-induced root hairs in Arabidopsis.

Cell fate and differentiation in the Arabidopsis root epidermis are genetically defined but remain plastic to environmental signals such as limited availability of inorganic phosphate (Pi). Root hairs of Pi-deficient plants are more frequent and longer than those of plants grown under Pi-replete conditions. To dissect genes involved in Pi deficiency-induced root hair morphogenesis, we constructed a co-expression network of Pi-responsive genes against a customized database that was assembled from experiments in which differentially expressed genes that encode proteins with validated functions in root hair development were over-represented. To further filter out less relevant genes, we combined this procedure with a search for common cis-regulatory elements in the promoters of the selected genes. In addition to well-described players and processes such as auxin signalling and modifications of primary cell walls, we discovered several novel aspects in the biology of root hairs induced by Pi deficiency, including cell cycle control, putative plastid-to-nucleus signalling, pathogen defence, reprogramming of cell wall-related carbohydrate metabolism, and chromatin remodelling. This approach allows the discovery of novel of aspects of a biological process from transcriptional profiles with high sensitivity and accuracy.

An Inventory of Nutrient-Responsive Genes in Arabidopsis Root Hairs.

Root hairs, single cell extensions of root epidermal cells that are critically involved in the acquisition of mineral nutrients, have proven to be an excellent model system for studying plant cell growth. More recently, omics-based systems biology approaches have extended the model function of root hairs toward functional genomic studies. While such studies are extremely useful to decipher the complex mechanisms underlying root hair morphogenesis, their importance for the performance and fitness of the plant puts root hairs in the spotlight of research aimed at elucidating aspects with more practical implications. Here, we mined transcriptomic and proteomic surveys to catalog genes that are preferentially expressed in root hairs and responsive to nutritional signals. We refer to this group of genes as the root hair trophomorphome. Our analysis shows that the activity of genes within the trophomorphome is regulated at both the transcriptional and post-transcriptional level with the mode of regulation being related to the function of the gene product. A core set of proteins functioning in cell wall modification and protein transport was defined as the backbone of the trophomorphome. In addition, our study shows that homeostasis of reactive oxygen species and redox regulation plays a key role in root hair trophomorphogenesis.

A MYB/ZML Complex Regulates Wound-Induced Lignin Genes in Maize.

Lignin is an essential polymer in vascular plants that plays key structural roles in vessels and fibers. Lignification is induced by external inputs such as wounding, but the molecular mechanisms that link this stress to lignification remain largely unknown. In this work, we provide evidence that three maize (Zea mays) lignin repressors, MYB11, MYB31, and MYB42, participate in wound-induced lignification by interacting with ZML2, a protein belonging to the TIFY family. We determined that the three R2R3-MYB factors and ZML2 bind in vivo to AC-rich and GAT(A/C) cis-elements, respectively, present in a set of lignin genes. In particular, we show that MYB11 and ZML2 bind simultaneously to the AC-rich and GAT(A/C) cis-elements present in the promoter of the caffeic acid O-methyl transferase (comt) gene. We show that, like the R2R3-MYB factors, ZML2 also acts as a transcriptional repressor. We found that upon wounding and methyl jasmonate treatments, MYB11 and ZML2 proteins are degraded and comt transcription is induced. Based on these results, we propose a molecular regulatory mechanism involving a MYB/ZML complex in which wound-induced lignification can be achieved by the derepression of a set of lignin genes.

AtMYB7, a new player in the regulation of UV-sunscreens in Arabidopsis thaliana.

The phenylpropanoid metabolic pathway provides a wide variety of essential compounds for plants. Together with sinapate esters, in Brassicaceae species, flavonoids play an important role in protecting plants against UV irradiation. In this work we have characterized Arabidopsis thaliana AtMYB7, the closest homolog of AtMYB4 and AtMYB32, described as repressors of different branches of phenylpropanoid metabolism. The characterization of atmyb7 plants revealed an induction of several genes involved in flavonol biosynthesis and an increased amount of these compounds. In addition, AtMYB7 gene expression is repressed by AtMYB4. As a consequence, the atmyb4 mutant plants present a reduction of flavonol contents, indicating once more that AtMYB7 represses flavonol biosynthesis. Our results also show that AtMYB7 gene expression is induced by salt stress. Induction assays indicated that AtMYB7 represses several genes of the flavonoid pathway, DFR and UGT being early targets of this transcription factor. The results obtained indicate that AtMYB7 is a repressor of flavonol biosynthesis and also led us to propose AtMYB4 and AtMYB7 as part of the regulatory mechanism controlling the balance of the main A. thaliana UV-sunscreens.

Cuantificación de la demamda insatisfecha en el tratamiento de la insuficiencia renal crónica

Actualmente una indefinida proporción de comunidad conoce sobre la existencia de la terapia de reemplazo renal. No obstante, a pesar de que la mayoría de los pacientes institucionales tiene acceso a ella, un gran número de los llamados "clasificados económicos" no pueden ser admitido en estos programas, con la consecuente mortalidad implicada. Emprendimos el presente estudio con el objeto de cuantificar con mayor exactitud las dimensiones de este fenómeno. Entre febrero y mayo de 1992, evaluamos prospectivamente todos los pacientes con insuficiencia renal crónica que consultaron HUSVP a quienes fue imposible ofrecerles este tratamiento. Encontramos 35 casos, 23 hombres (66 por ciento), con una edad promedio de 31+-2 años (rango 13 a 63), 17 (49 por ciento) procedían de Medellín y su área metropolitana, 23 (66 por ciento) eran casados, 24 (69 por ciento) provenían del área urbana, y 19 (54 por ciento) carecían de empleo. La etiología de la falla renal fue desconocida en 23 casos (66 por ciento). Las pruebas de función renal al momento de la evaluación fueron : nitrógeno ureico 137.4+-2.2 mg/dL (rango 60-200) y creatinina 16.3+-0.3 mg/dL (5.2-27.8). En todos los casos, la razón fundamental para no ser admitidos a diálisis o traspalnte renal fue su precaria situación socioeconómica; durante el período del estudio fueron recibidos dos enfermos en el programa de reemplazo renal, representando una satisfacción de la demanda de uno por cada 18.5 casos. En conclusión, aunque en nuestra Unidad realizamos 70 a 90 trasplantes y 6.000 a 7.000 diálisis por año, este trabajo demuestra la pobre satisfacción de la demanda de terapia de reemplazo renal en los enfermos sin seguridad social y la magnitud del problema que no logramos resolver.

Estudio de 224 donantes de riñón para trasplante con evaluación de calidad de vida posdonación en un subgrupo

Estudiamos los registros clínicos de 224 donantes de riñon para traspnate intrafamiliar, quienes fueron sometidos a nefrectomía (Nx) unilateral en nuestro hospital, entre agosto 1973 y febrero 1989. La edad promedio fue 31+- (ESM) años (rango 16-59); 123 (55 por ciento) fueron hombres y la relación donante-receptor fue : hermanos 162 (72 por ciento), padres 38 (17 por ciento) e hijos 24 (11 por ciento). La Nx fue 5.7+-0.3 días (rango 3-25). Buscamos la mayor parte de estos 224 donantes mediante cartas, llamadas y mensajes enviados a través de sus respectivos receptores; 140 (62 por ciento) respondieron. A este subgrupo se le interrogó sobre problemas médicos a partir de la Nx, se les practicó examne físico completo y se les hicieron prubas de función renal en nuestro laboratorio o en sus lugares de residencia. Comparamos los resulatdos con los de pre-Nx. La duración del seguimiento fue 51.1+-2.9 meses (rango 0.3-198). Ochenta y seis de los 140 respondieron un cuestionario sobre calidad de vida y actitudes frente a la donación. Para pre y post-Nx respectivamente, el paso fue 61.1+-0.7 y 63.2+- 1 Kg (NS), la presión arterial sistólica 123+-0.8 y 126+-1.4 mmHg (NS) y la diastólica 78+-0.5 y 79+-0.9 mmHg (NS). Los resulatdos de las pruebas de laboratorio pre y post-Nx fueron : creatinina 1.05+-0.2 y 1.29+-0.2 mg/dl (P<0.00001), nitrógeno ureico 10.3+-3.5 y 15.1+-5.3 mg/dl (P<0.00001), depuración de creatinina 94.3+-24.2 y 84.6+-18.2 ml/min (P=0.00021), y proteinuria 0.08+-0.12 y 0.07+-0.13 g/día (NS). Se hallaron valores de proteinuria post-Nx mayores de 0.3 g/día en 19 de 107 en los que se determinó (18 por ciento), con un valor máximo de 0.57 g/día. Hipertensión post-Nx ocurrió en tres casos (2.1 por ciento)...