RESUMO No melhoramento genético de eucalipto, existem ainda poucos instrumentos disponíveis para acelerar a seleção de genótipos superiores, e uma das principais estratégias sugeridas para se acelerar este processo é a identificação de marcadores moleculares ligados a caracteres de interesse. Foram avaliados 81 marcadores RAPD em uma progênie F1 de Eucalyptus grandis W. Hill ex Maiden segregante para o caractere florescimento precoce utilizando-se a técnica de Bulked Segregant Analysis (BSA). Dentre esses marcadores, um se mostrou relacionado ao caractere, sendo então convertido em Sequence Characterized Amplified Region (SCAR), avaliado em cada indivíduo da progênie e validado em outras progênies que apresentam o caractere. O SCAR mostrou-se informativo na progênie que apresenta um dos parentais como doador do fragmento polimórfico, com eficiência de 60%. Esses resultados descrevem o primeiro marcador SCAR desenvolvido para eucalipto e confirmam a utilidade da técnica de BSA como ferramenta molecular no melhoramento genético florestal e que poderia ser empregada para localização de marcadores ligados a diferentes caracteres silviculturais.

ABSTRACT There are few available tools in eucalyptus breeding to accelerate the selection of superior genotypes, and one of the main tools to improve this process is the use of molecular markers linked to traits of interest. Using “Bulked Segregant Analysis”, we evaluated 81 RAPD molecular markers in a Eucalyptus grandis W. Hill ex Maiden progeny that segregates for early flowering, and one marker was identified as related to this trait. This RAPD marker was converted into a Sequence-Characterized Amplified Region (SCAR), which was then evaluated in a F1 progeny, and validated in other progenies that presents this trait. The SCAR marker was informative in the progeny in which one of the parental was the donor of the band, with an efficiency of 60%. These results describe the first SCAR marker developed for eucalypt and confirm this technique as a useful molecular tool for forestry breeding which could be employed to locate markers linked to other silvicultural traits.

Boron (B) is a low mobility plant micronutrient whose molecular mechanisms of absorption and translocation are still controversial. Many factors are involved in tolerance to Boron excess or deficiency. Recently, the first protein linked to boron transport in biological systems, BOR1, was characterized in Arabidopsis thaliana. This protein is involved in boron xylem loading and is similar to bicarbonate transporters found in animals. There are indications that BOR1 is a member of a conserved protein family in plants. In this work, FORESTS database was used to identify sequences similar to this protein family, looking for a probable BOR1 homolog in eucalypt. We found five consensus sequences similar to BOR1; three of them were then used in multiple alignment analysis. Based on amino acid similarity and in silico expression patterns, a consensus sequence was identified as a candidate BOR1 homolog, helping deeper experimental assays that could identify the function of this protein family in Eucalyptus.

Até meados da década de 50 acreditava-se que o boro tinha uma importante função no transporte de açúcares em plantas. Na verdade, o boro depende de açúcares álcoois para serem mobilizados dentro da planta. Em alguns organismos os principais açúcares envolvidos neste processo são o sorbitol e o manitol, que formam complexos estáveis com o micronutriente. O objetivo deste estudo foi procurar seqüências no banco de dados SugarCane EST Genome Project (SUCEST) que codificam enzimas participantes na via metabólica destes açúcares através da comparação de enzimas de outros organismos. Dezoito "contigs" de cana-de-açúcar (Saccharum sp.) apresentaram similaridade com onze seqüências de enzimas que compõem a provável via metabólica de sorbitol e manitol a partir de frutose. Destes "contigs", sete apresentaram uma alta similaridade entre as seqüências depositadas no GenBank.

Until the mid 1950s, boron was believed to play an important role in the transport of sugars in plants. However, boron actually depends on sugar alcohols to be taken up by the plant. In some cases, the main sugars involved in this process are sorbitol and mannitol which form stable complexes with boron. In this study, the sequences of the SugarCane EST Genome Project (SUCEST) database were searched for enzymes involved in the metabolism of these sugars by comparing them with enzymes from other organisms. Eighteen contigs from sugarcane (Saccharum sp.) presented high similarity with 11 enzymes involved in the putative biosynthetic pathway of sorbitol and mannitol from fructose in sugarcane. Seven of these contigs had high homology with sequences deposited in GenBank.