The relationships between seed and pollen flow and cline discordance/concordance between cytoplasmic and nuclear genes, with the incorporation of the effects of natural selection, are formulated for one locus with two alleles, under assumptions of random mating, no drift and no mutation. Results show that under certain conditions, the relative roles of seed and pollen flow in shaping cline discordance/ concordance are very similar to their roles in influencing population differentiation for selectively neutral markers with different modes of inheritance. Where the disequilibria

MicroRNAs (miRNAs) have important roles in the regulation of genes; however, for trees few studies have explored the potential impact of the interactions between miRNAs and their target genes. Here, we performed transcript profiling and association genetics (single-SNP, haplotype-based and multi-SNP associations) to study the genetic regulatory relationship of Pto-miR257 and its 12 target genes in 435 individuals of a natural population of Populus tomentosa. Expression profiling of Pto-miR257 and its targets showed a negative relationship between their expression levels. Of the 61 single-nucleotide polymorphisms (SNPs) detected in Pto-miR257, 6 in the pre-mature region strongly affected its secondary stability and 1 in the mature region could alter its target spectrum. Among the 1029 SNPs in the targets, 3 were located in target sites that could change the binding affinity of Pto-miR257. Single-SNP association analysis revealed that SNPs in Pto-miR257 and target genes associated with both growth and wood property traits, in agreement with haplotype-based identifications. Multi-SNP association found that 10 targets shared at least one common trait with Pto-miR257, with phenotypic variance from 0.5 to 8.5%, suggesting a possible internal genetic interaction between them. Epistasis analysis showed significant epistatic interactions among Pto-miR257 and its targets. Therefore, our study demonstrated Pto-miR257 and its 12 targets had roles in wood formation and revealed the genetic interaction network between the miRNA and its targets under additive, dominant and epistatic models. Thus, association genetics can be used to decipher the interactions between miRNAs and their target genes and to help understand the genetic architecture of complex traits.