Estudos de variabilidade genética e dos genes de tolerância ao alumínio em espécies do género secale.
Ficheiros
Data
2010
Título da revista
ISSN da revista
Título do Volume
Editora
Resumo
O centeio (Secale cereale L.) é uma cultura importante pela sua capacidade de resistir e tolerar diversos stresses bióticos e abióticos. A toxicidade do alumínio (Al) limita o crescimento e a produtividade das culturas em solos ácidos, sendo o maior factor limitante para o crescimento das plantas, numa grande área Mundial. Tem sido descrita uma grande variabilidade na tolerância ao Al, entre espécies diferentes e dentro da mesma espécie, nas mais variadas culturas. Entre os cereais, o centeio é considerada a espécie mais tolerante. O género Secale inclui várias espécies silvestres e uma única espécie cultivada (S. cereale). Vários estudos têm sido efectuados no centeio cultivado para determinar o grau de tolerância ao Al e para caracterizar a sua variabilidade. No que respeita às espécies silvestres é muito pouco conhecido o seu comportamento relativamente à tolerância ao Al. Sendo as espécies de Secale, na sua maioria, alogâmicas, existe uma grande diversidade de genótipos, o que favorece a selecção natural do germoplasma mais adequado às diferentes condições edafo-climáticas. Este facto torna o centeio de extrema importância para utilização em programas de melhoramento genético de espécies afins e economicamente importantes. Para avaliar a diversidade genética têm sido desenvolvidos marcadores moleculares que permitem estudar as relações filogenéticas através da análise do grau de polimorfismo que as espécies apresentam. Os mecanismos da tolerância ao Al são diversos e dependentes da espécie em causa. A exsudação dos ácidos orgânicos foi descrita como um dos mecanismos implicados na tolerância ao Al e ganhou maior destaque com a recente clonagem dos genes que codificam a exsudação do malato (ALMT) e do citrato (MATE), pelas raízes, activada pelo Al. Neste trabalho, avaliou-se a resposta de cinco espécies/subespécies silvestres do género Secale, e quatro variedades/populações do centeio cultivado S. cereale. Foram utilizadas quatro testemunhas, duas sensíveis e duas tolerantes. Os resultados obtidos permitiram inferir da grande variabilidade existente na tolerância ao Al entre os vários genótipos de centeio estudados. Estudou-se a variabilidade genética deste material vegetal através dos marcadores RAPDs e ISSRs e determinaram-se as relações filogenéticas. Foram encontrados 436 marcadores de PCR (243 RAPDs e 193 ISSRs) onde 294 se revelaram polimórficos. A percentagem de polimorfismo detectada foi de 60,50 e 76,17 %, nos marcadores RAPDs e ISSRs, respectivamente. A análise dos resultados foi efectuada através do método UPGMA utilizando o coeficiente SM. A combinação destes marcadores originou um dendrograma no qual se agruparam onze centeios estudados. Com o objectivo de relacionar diferentes sequências com diferentes graus de tolerância foi iniciado um estudo de análise de sequências do gene MATE. Foram obtidas, a partir do gDNA, sequências de três exões do gene MATE, de plantas tolerantes e sensíveis das diferentes espécies, e verificou-se a existência de uma grande variabilidade.
Rye (Secale cereale L.) is an important crop due to its ability to resist and tolerate biotic and abiotic stresses. Aluminum (Al) toxicity limits growth and crop yield in acid soils and is the main limiting factor for plant growth in most parts of the world. A large variability in Al tolerance has been described among different species and within the same species, in several crops. Among cereals, rye is the most tolerant species. The genus Secale includes several wild species and one cultivated species (S. cereale). Several studies have been carried out on cultivated rye to determine the Al tolerance degree and to characterize the variability, relatively to wild ryes, there is few information about its behavior to Al tolerance. The Secale species are mostly allogamous allowing a great diversity of genotypes, which support the natural selection of germplasm adapted to different soil and climatic conditions. Rye can be used as a source of resistance genes for related species, namely wheat. Therefore, the knowledge of the mechanism and the genes that control Al tolerance in rye will provide fundamental information than can be used to increase Al tolerance in other cereals. To assess the genetic diversity, molecular markers have been developed to enable the study of phylogenetic relationships using the species polymorphism degree. There are several Al tolerance mechanisms described in different species. The mechanism that has been observed most commonly involves the release of organic anions such as malate, citrate, and oxalate from roots. A role for organic acid exudation as a mechanism of Al tolerance has been highlighted by the recent cloning of Al-tolerance genes that all encode organic acid transporters of malate (ALMT1) and citrate (MATE). In this study, five wild species/subspecies of the genus Secale and four varieties/populations of the cultivated rye, S. cereale, compared with four testers (two sensitive and two tolerant) were evaluated. The results showed a large variability of Al tolerance among the various genotypes of rye studied We studied the genetic variability of plant material using RAPD and ISSR markers, for determination of the phylogenetic relationships. 436 PCR markers (243 RAPDs and 193 ISSRs) were found being 294 polymorphic. The percentage of polymorphism detected was 60,50 and 70,17 % in RAPDs and ISSRs markers, respectively. The analysis was done with the UPGMA method using the SM coefficient. The combination of these markers produced a dendrogram grouping the eleven studied ryes. In order to relate different sequences with different tolerance degrees, a sequence analysis of MATE gene was initiated. Three exons sequences of the MATE gene were obtained from gDNA sequences of tolerant and sensitive plants of different species. It was found a great variability.
Rye (Secale cereale L.) is an important crop due to its ability to resist and tolerate biotic and abiotic stresses. Aluminum (Al) toxicity limits growth and crop yield in acid soils and is the main limiting factor for plant growth in most parts of the world. A large variability in Al tolerance has been described among different species and within the same species, in several crops. Among cereals, rye is the most tolerant species. The genus Secale includes several wild species and one cultivated species (S. cereale). Several studies have been carried out on cultivated rye to determine the Al tolerance degree and to characterize the variability, relatively to wild ryes, there is few information about its behavior to Al tolerance. The Secale species are mostly allogamous allowing a great diversity of genotypes, which support the natural selection of germplasm adapted to different soil and climatic conditions. Rye can be used as a source of resistance genes for related species, namely wheat. Therefore, the knowledge of the mechanism and the genes that control Al tolerance in rye will provide fundamental information than can be used to increase Al tolerance in other cereals. To assess the genetic diversity, molecular markers have been developed to enable the study of phylogenetic relationships using the species polymorphism degree. There are several Al tolerance mechanisms described in different species. The mechanism that has been observed most commonly involves the release of organic anions such as malate, citrate, and oxalate from roots. A role for organic acid exudation as a mechanism of Al tolerance has been highlighted by the recent cloning of Al-tolerance genes that all encode organic acid transporters of malate (ALMT1) and citrate (MATE). In this study, five wild species/subspecies of the genus Secale and four varieties/populations of the cultivated rye, S. cereale, compared with four testers (two sensitive and two tolerant) were evaluated. The results showed a large variability of Al tolerance among the various genotypes of rye studied We studied the genetic variability of plant material using RAPD and ISSR markers, for determination of the phylogenetic relationships. 436 PCR markers (243 RAPDs and 193 ISSRs) were found being 294 polymorphic. The percentage of polymorphism detected was 60,50 and 70,17 % in RAPDs and ISSRs markers, respectively. The analysis was done with the UPGMA method using the SM coefficient. The combination of these markers produced a dendrogram grouping the eleven studied ryes. In order to relate different sequences with different tolerance degrees, a sequence analysis of MATE gene was initiated. Three exons sequences of the MATE gene were obtained from gDNA sequences of tolerant and sensitive plants of different species. It was found a great variability.
Descrição
Dissertação de Mestrado em Genética Molecular Comparativa e Tecnológica
Palavras-chave
Secale cereale L , toxicidade do alumínio , acidez dos solos , marcadores moleculares , variabilidade genética