SummaryLateral root formation, the primary way plants increase their root mass, displays developmental plasticity in response to environmental changes. The aberrant lateral root formation (alf)4-1 mutation blocks the initiation of lateral roots, thus greatly altering root system architecture. We have positionally cloned the ALF4 gene and have further characterized its phenotype. The encoded ALF4 protein is conserved among plants and has no similarities to proteins from other kingdoms. The gene is present in a single copy in Arabidopsis. Using translational reporters for ALF4 gene expression, we have determined that the ALF4 protein is nuclear localized and that the gene is expressed in most plant tissues; however, ALF4 expression and ALF4's subcellular location are not regulated by auxin. These ®ndings taken together with further genetic and phenotypic characterization of the alf4-1 mutant suggest that ALF4 functions independent from auxin signaling and instead functions in maintaining the pericycle in the mitotically competent state needed for lateral root formation. Our results provide genetic evidence that the pericycle shares properties with meristems and that this tissue plays a central role in creating the developmental plasticity needed for root system development.

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Prunus serotina subsp. capulí es una especie arbórea, silvestre y tetraploide que se distribuye a lo largo del continente americano y está presente en el callejón interandino ecuatoriano. A pesar de su potencial económico en las industrias alimenticia, maderera y médica, existe poca información acerca de la historia y el cultivo del capulí en el país. Este estudio evaluó la diversidad genética de P.serotina en tres provincias de la sierra ecuatoriana. Se analizaron 88 individuos de capulí provenientes de Pichincha, Cañar y Azuay, mediante el uso de ocho marcadores microsatélites heterólogos. Se generó un dendrograma con su respectivo bootstrap, un análisis de coordenadas principales (PCoA), un análisis de Mantel y valores del índice de distancia genética (Fst). Los resultados muestran un grado moderado de variabilidad genética entre los individuos de capulí analizados, junto con un cierto nivel de diferenciación genética entre individuos siguiendo una distribución norte sur que no está relacionado con la distancia geográfica entre las muestras analizadas. Se discuten varias hipótesis que tratan de explicar estos resultados

Capuli (Prunus serotina subsp. capuli) is a tree species that is widely distributed in the northern Andes. In Prunus, fruit set and productivity appears to be limited by gametophytic self-incompatibility (GSI) which is controlled by the S-Locus. For the first time, this research reveals the molecular structure of the capuli S-RNase (a proxy for S-Locus diversity) and documents how S-Locus diversity influences GSI in the species. To this end, the capuli S-RNase gene was amplified and sequenced in order to design a CAPS (Cleaved Amplified Polymorphic Sequence) marker system that could unequivocally detect S-alleles by targeting the highly polymorphic C2–C3 S-RNase intra-genic region. The devised system proved highly effective. When used to assess S-Locus diversity in 15 P. serotina accessions, it could identify 18 S-alleles; 7 more than when using standard methodologies for the identification of S-alleles in Prunus species. CAPS marker information was subsequently used to formulate experimental crosses between compatible and incompatible individuals (as defined by their S-allelic identity). Crosses between heterozygote individuals with contrasting S-alleles resulted in normal pollen tube formation and growth. In crosses between individuals with exactly similar S-allele identities, pollen tubes often showed morphological alterations and arrested development, but for some (suspected) incompatible crosses, pollen tubes could reach the ovary. The latter indicates the possibility of a genotype-specific breakdown of GSI in the species. Overall, this supports the notion that S-Locus diversity influences the reproductive patterns of Andean capuli and that it should be considered in the design of orchards and the production of basic propagation materials.

AVANCES Identificación de alelos S asociados con autoincompatibilidad en individuos de capulí (Prunus serotina subsp. capulí) mediante la amplificación del Intrón I del gen de la S-RNasaIdentification of S alleles associated with self-incompatibility in capuli (Prunus serotina subsp. capulí) samples by amplification of the Intron I of the S-RNasa gene AbstractIn plants, gametophytic self-incompatibility is a genetic mechanism regulated by the S locus, which has evolved to prevent self-fertilization. In fruit crops, information regarding the allelic composition of the S locus is essential for the establishment of productive orchards, as this allelic composition defines compatible combinations between individuals. The identification and cloning of S-RNase genes in Prunus species has allowed the development of molecular techniques for the characterization of S genotypes in wild and less-studied species of the genus. In this study we evaluated 80 individuals of capulí (Prunus serotina subsp. capulí) collected from 8 provinces of the Ecuadorian highlands to determinate the degree of allelic diversity of the S locus in this species. The molecular characterization of S loci was performed using degenerate primers designed from conserved regions of the S-RNase gene of several Prunus species. PCR products were separated on agarose gels, classified based on band size and sequenced. Our results reveal the presence of 11 alleles across sampled individuals. Generally, identified alleles showed a high percentage of identity with S-locus sequences reported for other species of the genus and it can be speculated that these derive from a common ancestor. By contrast, sequences with a lower percentage of identity may have originated independently following the diversification of Prunus species. The results obtained in this study should be complemented with field tests to confirm the phenotypic behavior of the capuli individuals analyzed.