Selfing of a single monoecious Populus tremula tree produces viable males, females and “supermales”
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Even though “supermale” (YY) poplar individuals are rarely found in natural populations or breeding collections, they can arise and can be as viable as regular male and female plants.
Nearly all species of the genus Populus are dioecious, i.e., form male and female flowers on separate individuals. However, bisexual poplar can occasionally be found under natural conditions or during the breeding process. According to the XX/XY model of sex determination, “supermale” (YY) individuals should only occur in the selfed progeny of a genetically male (XY) tree and not in the one of a genetically female (XX) parent. We performed detailed molecular genetic analyses of a bisexual Populus tremula XY-individual (ZP8) and its selfed progeny. The ZP8 tree was confirmed as P. tremula by chloroplast and nuclear markers, and the progeny was genotyped by microsatellite markers to verify self-pollination. In the selfed progeny but also in about 420 different poplar individuals from several breeding programmes and the wild, the X and Y chromosomes were tracked using previously reported and newly developed markers. From two self-pollination experiments of the bisexual ZP8 tree, 39 S1-individuals were obtained. Application of X- and Y-specific molecular markers revealed 15 XY, 17 YY, and 7 XX individuals. Additional investigations of about 300 different poplar clones employed in several breeding programmes as well as about 120 individuals from wild populations revealed only three trees with two Y chromosomes. Indications for inbreeding depression in the selfed progeny were obtained during germination and glasshouse cultivation, but are independent from the sex chromosome combination. Even though YY-poplar individuals are rarely found in natural populations or breeding collections, they can arise and can be as viable as regular XY- and XX-plants.
KeywordsBisexual Dioecy Inbreeding Poplar Sex chromosome TOZ19
We thank K. Groppe, D. Ebbinghaus, M. Will, and O. Polak (all Thuenen-Institute of Forest Genetics, Grosshansdorf, Germany) for excellent technical assistance in the lab, and the Thuenen-Institute greenhouse staff (W. Graf, M. Hunger, G. Wiemann, R. Ebbinghaus, M. Spauszus) for plant cultivation. Thanks are due to Dr. B. Heinze (Federal Research Centre for Forests, Department of Forest Genetics, Vienna, Austria), Prof. A. Tsarev (All-Russian Research Institute of Forest Genetics, Voronezh, Russia), V. Schneck (Thuenen-Institute of Forest Genetics, Waldsieversdorf, Germany), M. Tubes (Bayerisches Amt für forstliche Saat- und Pflanzenzucht (ASP), Teisendorf, Germany), Dr. M. Meyer (TU Dresden, Dresden, Germany), Dr. H. Wolf (Staatsbetrieb Sachsenforst, Graupa, Germany), Dr. H. Liesebach, Dr. H. Schröder, Dr. M. Liesebach, and Dr. G. von Wühlisch (all Thuenen-Institute of Forest Genetics, Grosshansdorf, Germany), for providing plant material or DNA samples from P. tremula individuals. We also thank Prof. Dr. O. Nilsson (Umeå Plant Science Centre, Umeå, Sweden) for kindly providing the pHSP::AtFT gene construct. Funding was provided by a core grant of the Thünen Institute.
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Conflict of interest
The authors declare that they have no conflict of interest.
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