Nucleotide diversity and haplotype structure al phyB2, a putative QTL for bud phenology in Populus tremula

GARCÍA MV; PK INGVARSSON

Gattlinburg - USA

Simposio; 12th New Phytologist Symposium “Functional genomics of environmental adaptation in Populus; 2004

New Phytologist Trust

Phytochromes have a central role in mediating photoperiodic response and a major QTL for bud phenology in Populus co-locates with a member of the phytochromes gene family, phyB2. We have studied the patterns of DNA sequence variation in phyB2 in European aspen (Populus tremula) in an attempt to elucidate the genetic basis of bud phenology. We analyzed complete sequences of phyB2 in 24 individuals from four different sites throughout Europe (France, Austria, southem and northern Sweden). There was substantial nucleotide diversity in phyB2 (11:= 0.00927), on parwith several other genes in P. tremula. Also, Tajima D was significantly negative (D =-1.813), indicating an excess of singleton mutations. Selective constraint across the phyB2 gene was generally high, as evidence by a ratio of non-synonymous to synonymous diversities of 1rahrs=0.218. The same was true when divergence from P. trichocarpa was analyzed, as the KalKsratio was 0.236. Surprisingly, genetic differentiation among populations was low and not significant (Fst = 0.0083). Also, a neighbor-joining tree indicated that the phyB2 sequences are made up of two diverged sequence clusters, but they did not correspond to geographic origin of the samples.