Alma Piñeyro-Nelson

Transgenes in Mexican maize: molecular evidence and methodological considerations for GMO detection in landrace populations

A possible consequence of planting genetically modified organisms (GMOs) in centres of crop origin is unintended gene flow into traditional landraces. In 2001, a study reported the presence of the transgenic 35S promoter in maize landraces sampled in 2000 from the Sierra Juarez of Oaxaca, Mexico. Analysis of a large sample taken from the same region in 2003 and 2004 could not confirm the existence of transgenes, thereby casting doubt on the earlier results. These two studies were based on different sampling and analytical procedures and are thus hard to compare. Here, we present new molecular data for this region that confirm the presence of transgenes in three of 23 localities sampled in 2001. Transgene sequences were not detected in samples taken in 2002 from nine localities, while directed samples taken in 2004 from two of the positive 2001 localities were again found to contain transgenic sequences. These findings suggest the persistence or re‐introduction of transgenes up until 2004 in this area. We address variability in recombinant sequence detection by analyzing the consistency of current molecular assays. We also present theoretical results on the limitations of estimating the probability of transgene detection in samples taken from landraces. The inclusion of a limited number of female gametes and, more importantly, aggregated transgene distributions may significantly lower detection probabilities. Our analytical and sampling considerations help explain discrepancies among different detection efforts, including the one presented here, and provide considerations for the establishment of monitoring protocols to detect the presence of transgenes among structured populations of landraces.

Dispersal of Transgenes through Maize Seed Systems in Mexico

Objectives Current models of transgene dispersal focus on gene flow via pollen while neglecting seed, a vital vehicle for gene flow in centers of crop origin and diversity. We analyze the dispersal of maize transgenes via seeds in Mexico, the crops cradle. Methods We use immunoassays (ELISA) to screen for the activity of recombinant proteins in a nationwide sample of farmer seed stocks. We estimate critical parameters of seed population dynamics using household survey data and combine these estimates with analytical results to examine presumed sources and mechanisms of dispersal. Results Recombinant proteins Cry1Ab/Ac and CP4/EPSPS were found in 3.1% and 1.8% of samples, respectively. They are most abundant in southeast Mexico but also present in the west-central region. Diffusion of seed and grain imported from the United States might explain the frequency and distribution of transgenes in west-central Mexico but not in the southeast. Conclusions Understanding the potential for transgene survival and dispersal should help design methods to regulate the diffusion of germplasm into local seed stocks. Further research is needed on the interactions between formal and informal seed systems and grain markets in centers of crop origin and diversification.

Recent long‐distance transgene flow into wild populations conforms to historical patterns of gene flow in cotton (Gossypium hirsutum) at its centre of origin

Over 95% of the currently cultivated cotton was domesticated from Gossypium hirsutum, which originated and diversified in Mexico. Demographic and genetic studies of this species at its centre of origin and diversification are lacking, although they are critical for cotton conservation and breeding. We investigated the actual and potential distribution of wild cotton populations, as well as the contribution of historical and recent gene flow in shaping cotton genetic diversity and structure. We evaluated historical gene flow using chloroplast microsatellites and recent gene flow through the assessment of transgene presence in wild cotton populations, exploiting the fact that genetically modified cotton has been planted in the North of Mexico since 1996. Assessment of geographic structure through Bayesian spatial analysis, BAPS and Genetic Algorithm for Rule‐set Production (GARP), suggests that G. hirsutum seems to conform to a metapopulation scheme, with eight distinct metapopulations. Despite evidence for long‐distance gene flow, genetic variation among the metapopulations of G. hirsutum is high (He = 0.894 ± 0.01). We identified 46 different haplotypes, 78% of which are unique to a particular metapopulation, in contrast to a single haplotype detected in cotton cultivars. Recent gene flow was also detected (m = 66/270 = 0.24), with four out of eight metapopulations having transgenes. We discuss the implications of the data presented here with respect to the conservation and future breeding of cotton populations and genetic diversity at its centre of crop origin.

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

This article shows that the peculiar expression pattern of a functionally conserved floral gene (APETALA3-like) in the center of the Lacandonia schismatica flower underlies its unique inside-out arrangement (i.e., central stamens surrounded by carpels). Thus, relatively simple genetic alterations may underlie large morphological shifts fixed in extant natural populations. 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.

Resolution of the Mexican transgene detection controversy: error sources and scientific practice in commercial and ecological contexts

A. PINEYRO-NELSON,* J . VAN HEERWAARDEN,† H. R. PERALES,‡ J . A. SERRATOS-HERNANDEZ,§ A. RANGEL,– M. B. HUFFORD,** , P . GEPTS,* * A. GARAYARROYO,* R. RIVERA-BUSTAMANTE– and E. R. ALVAREZ-BUYLLA* *Laboratorio de Genetica Molecular, Desarrollo y Evolucion de Plantas, Dpto. de Ecologia Funcional, Instituto de Ecologia, UNAM, Tercer Circuito Exterior, Junto al Jardin Botanico, Mexico DF 04510, Mexico, †C.T. de Wit Graduate School for Production Ecology & Resource Conservation (PE&RC), Laboratory of Plant Breeding, Waageningen University, P.O. Box 386, 6700 AJ Wageningen, The Netherlands, ‡Departamento de Agroecologia, El Colegio de la Frontera Sur, Carretera Panamericana y Periferico Sur s ⁄ n, San Cristobal, Chiapas, Mexico, Universidad Autonoma de la Ciudad de Mexico. Coordinacion Academica. Avenida Division del Norte 906, Narvarte Poniente 03020, Mexico DF, Mexico, –CINVESTAV Irapuato, Km. 9.6 Libramiento Norte, Carretera Irapuato-Leon. A.P. 629, C.P. 36500 Irapuato, Guanajuato, Mexico, **Department of Plant Sciences ⁄MS1, University of California, Davis, CA 95616, USA

When ABC becomes ACB

Understanding how the information contained in genes is mapped onto the phenotypes, and deriving formal frameworks to search for generic aspects of developmental constraints and evolution remains one of the main challenges of contemporary biological research. The Mexican endemic triurid Lacandonia schismatica (Lacandoniaceae), a mycoheterotrophic monocotyledonous plant with hermaphroditic reproductive axes is alone among 250,000 species of angiosperms, as it has central stamens surrounded by a peripheral gynoecium, representing a natural instance of a homeotic mutant. Based on the classical ABC model of flower development, it has recently been shown that the B-function gene APETALA3 (AP3), essential for stamen identity, was displaced toward the flower centre in L. schismatica (ABC to ACB) from the early stages of flower development. A functional conservation of B-function genes from L. schismatica through the rescue of B-gene mutants in Arabidopsis thaliana, as well as conserved protein interactions, has also been demonstrated. Thus, it has been shown that relatively simple genetic alterations may underlie large morphological shifts fixed in extant natural populations. Nevertheless, critical questions remain in order to have a full and sufficient explanation of the molecular genetic mechanisms underlying L. schismaticas unique floral arrangement. Evolutionary approaches to developmental mechanisms and systems biology, including high-throughput functional genomic studies and models of complex developmental gene regulatory networks, constitute two main approaches to meet such a challenge. In this review, the aim is to address some of the pending questions with the ultimate goal of investigating further the mechanisms of L. schismaticas unique homeotic flower arrangement and its evolution.