Genetic structure of Populus hybrid zone along the Irtysh River provides insight into plastid-nuclear incompatibility.
In plants, the maintenance of species integrity despite hybridization has often been explained by the co-adaption of nuclear gene complexes. However, the interaction between plastid and nuclear sub-genomes has been underestimated. Here, we analyzed the genetic structure of a Populus alba and P. tremula hybrid zone along the Irtysh River system in the Altai region, northwest China, using both nuclear microsatellites and plastid DNA sequences. We found high interspecific differentiation, although the hybrid P. × canescens was prevalent. Bayesian inference classified most hybrids into F1, followed by a few back-crosses to P. alba, and fewer F2 hybrids and back-crosses to P. tremula, indicating a few introgressions but preference toward P. alba. When plastid haplotypes in parental species were distinct, P. × canescens carried the haplotypes of both parents, but showed significant linkage between intraspecific haplotype and nuclear genotypes at several microsatellite loci. Selection, rather than migration and assortative mating, might have contributed to such plastid-nuclear disequilibria. By removing later-generated hybrids carrying interspecific combinations of haplotype and nuclear genotypes, plastid-nuclear incompatibility has greatly limited the gene exchange between P. alba and P. tremula via backcrossing with hybrids, demonstrating a significant association between plastid haplotype and the proportion of nuclear admixture.
State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation, State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.
Yan-Fei
YF
Zeng
State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation, State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.|Collaborative Innovation Center of Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing, China.
Jian-Guo
JG
Zhang
State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation, State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.
Ai-Guo
AG
Duan
Forest Research Institute of the Altai Region, Xinjiang, China.
Bawerjan
B
Abuduhamiti
D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics*; D008040:Genetic Linkage; D014644:Genetic Variation; D005828:Genetics, Population; D006239:Haplotypes; D018087:Plastids / Q000235:genetics*; D032107:Populus / Q000235:genetics*; D045483:Rivers