B-Function Expression in the Flower Center Underlies the Homeotic Phenotype of Lacandonia schismatica (Triuridaceae)

Spontaneous homeotic transformations have been described in natural populations of both plants and animals, but little is known about the molecular-genetic mechanisms underlying these processes in plants. In the ABC model of floral organ identity in Arabidopsis thaliana, the B- and C-functions are necessary for stamen morphogenesis, and C alone is required for carpel identity. We provide ABC model-based molecular-genetic evidence that explains the unique inside-out homeotic floral organ arrangement of the monocotyledonous mycoheterotroph species Lacandonia schismatica (Triuridaceae) from Mexico. Whereas a quarter million flowering plant species bear central carpels surrounded by stamens, L. schismatica stamens occur in the center of the flower and are surrounded by carpels. The simplest explanation for this is that the B-function is displaced toward the flower center. Our analyses of the spatio-temporal pattern of B- and C-function gene expression are consistent with this hypothesis. The hypothesis is further supported by conservation between the B-function genes of L. schismatica and Arabidopsis, as the former are able to rescue stamens in Arabidopsis transgenic complementation lines, and Ls-AP3 and Ls-PI are able to interact with each other and with the corresponding Arabidopsis B-function proteins in yeast. Thus, relatively simple molecular modifications may underlie important morphological shifts in natural populations of extant plant taxa

An AGAMOUS-related MADS-box gene, XAL1 (AGL12), regulates root meristem cell proliferation and flowering transition in Arabidopsis

11 pages, 5 figures, 1 table.-- PMID: 18203871 [PubMed].-- PMCID: PMC2259045.-- Supplementary information available at: http://www.plantphysiol.org/cgi/content/full/pp.107.108647/DC1MADS-box genes are key components of the networks that control the transition to flowering and flower development, but their role in vegetative development is poorly understood. This article shows that the sister gene of the AGAMOUS (AG) clade, AGL12, has an important role in root development as well as in flowering transition. We isolated three mutant alleles for AGL12, which is renamed here as XAANTAL1 (XAL1): Two alleles, xal1-1 and xal1-2, are in Columbia ecotype and xal1-3 is in Landsberg erecta ecotype. All alleles have a short-root phenotype with a smaller meristem, lower rate of cell production, and abnormal root apical meristem organization. Interestingly, we also encountered a significantly longer cell cycle in the strongest xal1 alleles with respect to wild-type plants. Expression analyses confirmed the presence of XAL1 transcripts in roots, particularly in the phloem. Moreover, XAL1beta-glucuronidase expression was specifically up-regulated by auxins in this tissue. In addition, mRNA in situ hybridization showed that XAL1 transcripts were also found in leaves and floral meristems of wild-type plants. This expression correlates with the late-flowering phenotypes of the xal1 mutants grown under long days. Transcript expression analysis suggests that XAL1 is an upstream regulator of SOC, FLOWERING LOCUS T, and LFY. We propose that XAL1 may have similar roles in both root and aerial meristems that could explain the xal1 late-flowering phenotype.This work was supported by Consejo Nacional de Ciencia y Tecnología (CONACYT), México (grant nos. CO1.41848/A–1, CO1.0538/A–1, and CO1.0435.B–1); Dirección General de Asuntos del Personal Académico (DGAPA)-Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT), Universidad Nacional Autónoma de México (UNAM; grant nos. IN230002 and IX207104); and the University of California-MEXUS ECO IE 271 to E.R.A.-B. R.T.-L. was a recipient of CONACYT and DGAPA-PAPIIT-UNAM fellowships (no. IX225304). J.G.D. was supported by DGAPA-PAPIIT-UNAM (grant nos. IN210202 and IN225906) and CONACYT (grant no. 49267).Peer reviewe

Floral Morphogenesis: Stochastic Explorations of a Gene Network Epigenetic Landscape

In contrast to the classical view of development as a preprogrammed and deterministic process, recent studies have demonstrated that stochastic perturbations of highly non-linear systems may underlie the emergence and stability of biological patterns. Herein, we address the question of whether noise contributes to the generation of the stereotypical temporal pattern in gene expression during flower development. We modeled the regulatory network of organ identity genes in the Arabidopsis thaliana flower as a stochastic system. This network has previously been shown to converge to ten fixed-point attractors, each with gene expression arrays that characterize inflorescence cells and primordial cells of sepals, petals, stamens, and carpels. The network used is binary, and the logical rules that govern its dynamics are grounded in experimental evidence. We introduced different levels of uncertainty in the updating rules of the network. Interestingly, for a level of noise of around 0.5–10%, the system exhibited a sequence of transitions among attractors that mimics the sequence of gene activation configurations observed in real flowers. We also implemented the gene regulatory network as a continuous system using the Glass model of differential equations, that can be considered as a first approximation of kinetic-reaction equations, but which are not necessarily equivalent to the Boolean model. Interestingly, the Glass dynamics recover a temporal sequence of attractors, that is qualitatively similar, although not identical, to that obtained using the Boolean model. Thus, time ordering in the emergence of cell-fate patterns is not an artifact of synchronous updating in the Boolean model. Therefore, our model provides a novel explanation for the emergence and robustness of the ubiquitous temporal pattern of floral organ specification. It also constitutes a new approach to understanding morphogenesis, providing predictions on the population dynamics of cells with different genetic configurations during development

Longitudinal zonation pattern in Arabidopsis root tip defined by a multiple structural change algorithm

Background and Aims The Arabidopsis thaliana root is a key experimental system in developmental biology. Despite its importance, we are still lacking an objective and broadly applicable approach for identification of number and position of developmental domains or zones along the longitudinal axis of the root apex or boundaries between them, which is essential for understanding the mechanisms underlying cell proliferation, elongation and differentiation dynamics during root development. Methods We used a statistics approach, the multiple structural change algorithm (MSC), for estimating the number and position of developmental transitions in the growing portion of the root apex. Once the positions of the transitions between domains and zones were determined, linear models were used to estimate the critical size of dividing cells (L(critD)) and other parameters. Key Results The MSC approach enabled identification of three discrete regions in the growing parts of the root that correspond to the proliferation domain (PD), the transition domain (TD) and the elongation zone (EZ). Simultaneous application of the MSC approach and G2-to-M transition (CycB1;1DB:GFP) and endoreduplication (pCCS52A1:GUS) molecular markers confirmed the presence and position of the TD. We also found that the MADS-box gene XAANTAL1 (XAL1) is required for the wild-type (wt) PD increase in length during the first 2 weeks of growth. Contrary to wt, in the xal1 loss-of-function mutant the increase and acceleration of root growth were not detected. We also found alterations in L(critD) in xal1 compared with wt, which was associated with longer cell cycle duration in the mutant. Conclusions The MSC approach is a useful, objective and versatile tool for identification of the PD, TD and EZ and boundaries between them in the root apices and can be used for the phenotyping of different genetic backgrounds, experimental treatments or developmental changes within a genotype. The tool is publicly available at www.ibiologia.com.mx/MSC_analysis

El Centro de Ciencias de la Complejidad de la UNAM: Piedra de Roseta para la ciencia en México

El presente artículo explica el surgimiento del enfoque de la complejidad ante las carencias de la ciencia reduccionista, no obstante sus notables éxitos en el conocimiento de la materia y en el desarrollo tecnológico derivado del mismo. Se expone el fenómeno de la emergencia a partir del reconocimiento de niveles jerárquicos de organización dentro de la ciencia y se describen los sistemas complejos, destacando que las interacciones de las partes que los componen implican comportamientos que generan información adicional, usualmente oculta al observador. Por otro lado, se discuten las barreras para acceder a la transdisciplina, resaltando la dificultad de comunicación entre las especialidades debida a la existencia de lenguajes, métodos e ideas diferentes. Respecto a la posibilidad de explorar mejores formas de comunicación entre especialistas para incidir en la solución de problemas complejos se expone el origen y las perspectivas del Centro de Ciencias de la Complejidad (C3) de la UNAM

Linear Causation Schemes in Post-genomic Biology: The Subliminal and Convenient One-to-one Genotype-Phenotype Mapping Assumption

Abstract | In this essay we question the validity of basic assumptions in molecular biology and evolution on the basis of recent experimental data and through the lenses of a systems and nonlinear perspective. We focus our discussion on two well-established foundations of biology: the flow of information in molecular biology (i.e., the central dogma of molecular biology), and the “causal” linear signaling pathway paradigm.Under both paradigms the subliminal assumption of a one-to-one genotype-phenotype mapping (GPM) constitutes an underlying working hypothesis in many cases. We ask if this is empirically sustainable in post-genomic biology. We conclude that when embracing the notion of complex networks and dynamical processes governing cellular behavior — a view now empirically validated — one-to-one mapping can no longer be sustained. We hypothesize that such subliminal and sometimes explicit assumption may be upheld, to a certain degree, because it is convenient for the private appropriation and marketing of scientific discoveries. Hopefully, our discussion will help smooth the undergoing transition towards a more integrative, explanatory, quantitative and multidisciplinary systems biology. The latter will likely also yield more preventive and sustainable medical and agricultural developments, respectively, than a reductionist approach

Homeótica: el juego de lo inesperado y lo inevitable en la historia de la morfogénesis multicelular

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