M. Pérez de la Vega

Plant genetic adaptedness to climatic and edaphic environment

SummaryGenetic adaptation implies the shaping of population and species gene pools in response to environmental challenges. The two components of the abiotic land environment are climate and soil, both of which determine much of the evolutionary adaptedness of plants as, besides representing a set of surrounding physical, chemical and sometimes limiting traits, they determine the availability of nutrients and energy, of which they are the immediate source. Ecogeographical distribution of species and ecotypes and different physiological mechanisms and developmental patterns are good evidence of plant adaptedness to soil and climate. However, it is not always easy to determine the underlying genetics of adaptive processes, because 1) environmental factors to which the plants are responding are not always evident and are sometimes too complex, 2) several genes may be involved in the response to a given environmental factor, and 3) the same gene/s may be involved in different adaptive responses. In particular, data on Avena species and temperature as a key environmental factor will be used to illustrate some examples of climatic and edaphic adaptedness. Temperature affects the genetic evolution and geographical distribution of all organisms, and a great deal of evidence indicates that species and populations are genetically adapted to different temperature regimes. Isozymes and other molecular markers have helped in the understanding of the genetic basis of adaptedness. There are many examples of correlation between isozyme and DNA-marker variation and environmental differences. For many population geneticists, isozyme markers are just genetic markers with little or no direct involvement in adaptation. However, metabolic processes are controlled by enzymes, influenced by the environment and used to react in response to it. Evidence that isozymes, and perhaps other molecular polymorphisms, are directly involved in adaptedness will be also presented. Molecular genetic analyses at gene and population levels are opening the ways to a better understanding of plant genetic adaptation.Genetic adaptation implies the shaping of population and species gene pools in response to environmental challenges. The two components of the abiotic land environment are climate and soil, both of which determine much of the evolutionary adaptedness of plants as, besides representing a set of surrounding physical, chemical and sometimes limiting traits, they determine the availability of nutrients and energy, of which they are the immediate source. Ecogeographical distribution of species and ecotypes and different physiological mechanisms and developmental patterns are good evidence of plant adaptedness to soil and climate. However, it is not always easy to determine the underlying genetics of adaptive processes, because 1) environmental factors to which the plants are responding are not always evident and are sometimes too complex, 2) several genes may be involved in the response to a given environmental factor, and 3) the same gene/s may be involved in different adaptive responses. In particular, data on Avena species and temperature as a key environmental factor will be used to illustrate some examples of climatic and edaphic adaptedness. Temperature affects the genetic evolution and geographical distribution of all organisms, and a great deal of evidence indicates that species and populations are genetically adapted to different temperature regimes. Isozymes and other molecular markers have helped in the understanding of the genetic basis of adaptedness. There are many examples of correlation between isozyme and DNA-marker variation and environmental differences. For many population geneticists, isozyme markers are just genetic markers with little or no direct involvement in adaptation. However, metabolic processes are controlled by enzymes, influenced by the environment and used to react in response to it. Evidence that isozymes, and perhaps other molecular polymorphisms, are directly involved in adaptedness will be also presented. Molecular genetic analyses at gene and population levels are opening the ways to a better understanding of plant genetic adaptation.

Isolation of (GA)n Microsatellite Sequences and Description of a Predicted MADS-box Sequence Isolated from Common Bean (Phaseolus vulgaris L.)

The isolation of (GA)n microsatellites using a highly microsatellite-enriched library is described for the first time in common bean (Phaseolus vulgaris L.). A relatively simple and effective method to isolate DNA repeats from microsatellite-enriched libraries based on hybridization-capture of repeat regions using biotin-conjugated oligonucleotids and non-radioactive colony hybridization was carried out. PCR products from 200 to 800 bp were obtained and cloned. Of the 60 clones sequenced, 21 yielded (GA)n microsatellites with n values equal or higher than six. These (GA)n microsatellite-containing loci could be useful for further genetic mapping studies. A (GA)n microsatellite linked to a putative MADS-box gene was identified. This sequence, which represents the first MADS-box locus described to date in common bean, showed a very high similarity with other known MADS-box sequences and was grouped within the AGL2 subfamily cluster of the Arabidopsis MADS-box genes. The vicinity of microsatellites to some genes is also discussed.

Phylogenetic relationships inSecale (Poaceae): An isozymatic study

The genetic frequencies of 9 isozyme loci have been estimated in 23 samples of 4 species ofSecale by means of starch gel electrophoresis. The populations ofS. silvestre andS. vavilovii were monomorphic and uniform within each species, those ofS. montanum andS. cereale were polymorphic for most of the isozyme loci. On the basis of isozyme patterns as well as allelic and genotypic frequencies of isozyme loci,S. silvestre can be distinguished fromS. vavilovii, and both fromS. cereale andS. montanum; but there is no clear differentiation between the two latter species. Clusters constructed from genetic distances separateS. silvestre andS. vavilovii, whereasS. cereale andS. montanum were grouped together. The isozymatic data presented here, along with cytogenetic and life habit data, agree with the generally admitted existence of 4 species inSecale, and support the relationships suggested byKhush & Stebbins (1961).

The structure of the rDNA intergenic spacer of Avena sativa L.: a comparative study

The sequence of the 18S–25S ribosomal RNA gene intergenic spacer (IGS) of Avena sativa was determined. DNA was cloned after polymerase chain reaction amplification of the IGS. The spacer of 3980 bp is composed of non-repeated sequences and five tandem arrays of repeated sequences, named A to E. Homology between oats IGS and other grass species was found. Tandem arrays D and E seem to be originated by duplication from single-copy sequences in related species. A transcription initiation site and putative sites of termination, processing and methylation were detected by computer-aided search. These sites resemble motifs conserved in the IGS of plant species.

A comparative study of the structure of the rDNA intergenic spacer of Lens culinaris Medik., and other legume species

As part of a project on lentil molecular genetics, the sequence of the 18S-25S ribosomal RNA gene intergenic spacer (IGS) of Lens culinaris Medik. was determined. DNA was cloned after polymerase chain reaction (PCR) amplification. The spacer of 2939 bp was composed of nonrepetitive sequences and four tandem arrays of repeated sequences, named A to D. C and D arrays were formed by the repetition of very short consensus sequences. Similarity was found between lentil and other legume species, in particular those of the Vicieae tribe. A transcription initiation site, putative sites of termination and processing, and promoter-enhancer sequences were detected by computer-aided searches. These sites resemble motifs conserved in the IGS sequences of other plant species. The conservation of motifs in the otherwise highly variable plant IGS sequences points to the relevance of these motifs as functional sequences.

Intergenic ribosomal spacer variability in hexaploid oat cultivars and landraces

The variability of the ribosomal DNA intergenic spacer (IGS) was analysed in 58 cultivars from a worldwide collection and 14 Spanish landraces of hexaploid oats. IGS sequences were amplified by the polymerase chain reaction using primers complementary to conserved sequences of the ribosomal genes. Twelve IGS length variants ranging from 4090 to 3210 bp were observed; some are frequent and distributed worldwide whereas others seem to be restricted to Spanish landraces. Variability in length variant patterns among cultivars and landraces was extensive: a total of 28 different patterns was observed, which included two to six length variants. No variation was detected within cultivars except in six Spanish landraces. Length variants and patterns were unevenly distributed between bred cultivars, in which the longest were frequent, and landraces, in which some of the shortest were observed. No differentiation was found between spring and winter sown material. The possible relationship between IGS length variants and breeding and environmental adaptive responses, other than those related to the spring or winter habit, are discussed.

Genetic variation in common and runner bean of the Northern Meseta in Spain

The genetic variation within and between Spanish landraces or varieties of Phaseolus vulgaris L. (common bean) and P. coccineus L. (runner bean) has been estimated by means of isozymes and random amplified polymorphic DNA (RAPD) analyses. Likewise, storage protein and amino acid content in dry seeds have been estimated. Fifteen landraces (60 accessions) of P. vulgaris and six of P. coccineus (six accessions) have been studied. Of the seven isozymatic systems analyzed only three systems and three loci showed variability in each species. Isozyme analyses revealed that genetic variability within and between landraces exist in both species. Even variability within accession was detected in some P. vulgaris landraces. Comparison of isozyme data indicated that Spanish landraces have a lower level of genetic variability than wild American materials and probably also lower than American landraces. RAPD analysis allowed for the uniquely distinguishing of all landraces. Genetic similarity among landraces, estimated by both isozymes and RAPDs, were not related with the seed morphological characters (color, size and shape) which define each variety or landrace. Variation in protein and amino acid content among landraces was also detected. The average protein content in common bean (20.48%) was similar to values previously reported in this species and higher than the average in the runner bean landraces (16.33%). In relation to the amino acid content methionine and cysteine showed the lowest values in all samples, although the content of these two amino acids varied widely among landraces.

Ecogeographical distribution and differential adaptedness of multilocus allelic associations in Spanish Avena sativa L.

We determined the nine-locus isozyme genotype of 267 landrace accessions of Avena sativa from 31 provinces of Spain. Our results establish that level of genetic variability is usually high both within and among accessions of this heavily self-fertilizing hexaploid grass and that multilocus genetic structure differs in various ecogeographical regions of Spain. We concluded that selection favoring different multilocus genotypes in different environments was the main integrating force that shaped the internal genetic structure of local populations as well as the overall adaptive landscape of A. sativa in Spain. Implications in genetic resource conservation and utilization are discussed.

Genetic variability evaluation in a Moroccan collection of barley, Hordeum vulgare L., by means of storage proteins and RAPDs

The genetic variation existing in a set of barley (Hordeum vulgare L.) landrace samples recently collected in Morocco was estimated. Two kinds of genetic markers, seed storage proteins (hordeins) and random amplified polymorphic DNA (RAPD), were used. Only six out of 31 landraces were subjected to RAPD analysis. Both kinds of markers, RAPD and storage proteins, yielded similar results, showing that the level of variation observed in Moroccan barley was high: all landraces showed variability; 808 different storage protein patterns (multilocus associations) were observed among 1897 individuals (2.32 seeds per association, on average) with an average of 43 multilocus associations per accession. In general, genetic variation within accessions was higher than between accessions. The 100 polymorphic RAPD bands generated by 21 effective primers were able to generate enough patterns to differentiate between uniform cultivars and even between individuals in variable accessions. One of the aims of this work was to compare the effectiveness of RAPD versus storage protein techniques in assessing the variability of genetic resource collections. On average hordeins were more polymorphic than RAPDs: they showed more alternatives per band on gels and a higher percentage of polymorphic bands, although RAPDs supply a higher number of bands. Although RAPD is an easy and standard technique, storage protein analysis is technically easier, cheaper and needs less sophisticated equipment. Thus, when resources are a limiting factor and considering the cost of consumables and work time, seed storage proteins must be the technique of choice for a first estimation of genetic variation in plant genetic resource collections.

Genetic mapping of isozyme loci in Secale cereale L.

SummaryThe genetics and linkage relationships of several isozymatic and morphological markers have been investigated in different cultivars of rye (Secale cereale L.). The inheritance and the variability among cultivars of three new isozymatic zones are described: GOT2 and LAP, each of them under the control of a two-allele single locus, namely Got2 and Lap, respectively; and 6PGD1 controlled by two loci, 6Pgd1a and 6Pgd1b, which have alleles in common. Four linkage groups have been found: Acp2-Acp3, Got3-Mdh2-Lper4, Mdh1-6Pgd2-Pgi2, and Pgm-Eper2-[Eper1-Eper3]. The assignment of these four groups to the chromosomes 7R, 3R, 1R, and 4R is discussed.