Plant & Animal Genome VI Conference Plant & Animal Genome VI Conference
W30
Genetic markers based on PCR amplification of simple sequence repeats
(SSR) have become the standard for genetic mapping particularly in
mammals and increasingly so in plants. We are developing a reference
genetic linkage map for Eucalyptus species based on microsatellite
markers. We are integrating SSR segregation data on existing RAPD and
AFLP maps. A reference map of codominant multiallelic markers will
provide locus bridges between parental maps and make available a number
of anchor loci for fine resolution mapping of QTL alleles and
comparative mapping in species of the same genus. We have shown, based
on the isolation of dinucleotide repeats (AG and AC) from libraries of
E. grandis and E. urophylla (Brondani et al., 1997 submitted), that AG
repeats are more abundant than AC in Eucalyptus. From 180 useful
sequences based on dinucleotides, a screening of 103 primer pairs in
parents and 6 F1 progeny revealed that 35% of primer pairs amplified
easily interpretable products; 37% well-resolved and interpretable, and
28% that needed further optimization of PCR conditions. So far, a total
of 25 SSR based markers were mapped onto the existing maps. Fourteen of
these, were fully informative (all 4 alleles detected) in Metaphor
agarose gels. These markers were mapped on both parental maps allowing
the alignment of the respective linkage groups. A transportability of
mapped SSR markers of 85% was found among 7 commercially important
species of the same subgenus (Symphyomyrtus). This allows the
contemplation of a subgenus reference linkage map useful for QTL mapping
across species. Recently we have completed a survey based on the direct
hybridization of digested genomic DNA with different probes of tri (AAC,
TAA, AGA and TCA) and tetranucleotides (TGAG, ACAG, GATA and GAAA)
motifs to determine their relative abundance and distribution in the
genome. The amplification of products derived from tri and
tetranucleotide classes of simple sequence repeat should alleviate the
problem of trying to score allelic variants with small size differences.
Acknowledgments: PADCT-FINEP, CAPES.