Is natural selection maintaining alternate alleles at ABI1B, a candidate gene for bud phenology in Populus tremula?

GARCÍA, MV; PK INGVARSSON

Umeå - Suecia

Simposio; Oikos Symposium; 2005

Swedish Society of Ecology

Abscisic acid (ABA)is phytohormone involved in many aspects of plant growth and development, including dormancy. In Populus, a gene involved in ABA regulation (AB1B) co-locates with QTLs for several bud phenology traits. We have studied patterns of DNA sequence variation in ABIIB in Populus tremula from four different sites throughout Europe in an attempt to elucidate the genetic basis of dormancy. Sequence diversity was rather low, compared to other P. tremula genes (26 segregating sites, nucleotide diversity=3.57x 10-3 and theta= 4.1 x 10-3). However, there was a marked excess of polymorphism at non-synonymous sites (3.34xl0-3) compared to synonymous sites (1.9xl0-3), suggesting that selection has shaped patterns of variation at AB1B. In exon 4, two non-synonymous mutations segregate at intermediate frequencies. In addition to the base pair substitutions, a 170 bp deletion in intron 4 also segregate at an intermediate frequency. There is no apparent geographic structure to these polymorphisms but there is extensive linkage disequilibrium surrounding the deletion and the two polymorphic  sites, suggesting that natural selection may be maintaining two alternate alleles at the ABlB locus.