Multiple Events of Allopolyploidy in the Evolution of the Racemose Lineages in Prunus (Rosaceae) Based on Integrated Evidence from Nuclear and Plastid Data.
Prunus is an economically important genus well-known for cherries, plums, almonds, and peaches. The genus can be divided into three major groups based on inflorescence structure and ploidy levels: (1) the diploid solitary-flower group (subg. Prunus, Amygdalus and Emplectocladus); (2) the diploid corymbose group (subg. Cerasus); and (3) the polyploid racemose group (subg. Padus, subg. Laurocerasus, and the Maddenia group). The plastid phylogeny suggests three major clades within Prunus: Prunus-Amygdalus-Emplectocladus, Cerasus, and Laurocerasus-Padus-Maddenia, while nuclear ITS trees resolve Laurocerasus-Padus-Maddenia as a paraphyletic group. In this study, we employed sequences of the nuclear loci At103, ITS and s6pdh to explore the origins and evolution of the racemose group. Two copies of the At103 gene were identified in Prunus. One copy is found in Prunus species with solitary and corymbose inflorescences as well as those with racemose inflorescences, while the second copy (II) is present only in taxa with racemose inflorescences. The copy I sequences suggest that all racemose species form a paraphyletic group composed of four clades, each of which is definable by morphology and geography. The tree from the combined At103 and ITS sequences and the tree based on the single gene s6pdh had similar general topologies to the tree based on the copy I sequences of At103, with the combined At103-ITS tree showing stronger support in most clades. The nuclear At103, ITS and s6pdh data in conjunction with the plastid data are consistent with the hypothesis that multiple independent allopolyploidy events contributed to the origins of the racemose group. A widespread species or lineage may have served as the maternal parent for multiple hybridizations involving several paternal lineages. This hypothesis of the complex evolutionary history of the racemose group in Prunus reflects a major step forward in our understanding of diversification of the genus and has important implications for the interpretation of its phylogeny, evolution, and classification.
College of Life Sciences, Northwest A&F University, Yangling, Shaanxi, 712100, China.
Liang
L
Zhao
College of Life Sciences, Jianghan University, Wuhan, Hubei, 430056, China.
Xi-Wang
XW
Jiang
Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences / Shanghai Chenshan Botanical Garden, 3888 Chenhua Road, Songjiang, Shanghai, 201602, China.
Yun-Juan
YJ
Zuo
School of Applied Chemistry and Biological Engineering, Weifang Engineering Vocational College, Qingzhou, Shandong, 262500, China.
Xiao-Lin
XL
Liu
Department of Plant Sciences, MS2, University of California Davis, Davis, California, 95616, United States of America.
Siew-Wai
SW
Chin
Department of Biology, Pacific Lutheran University, Tacoma, Washington, 98447, United States of America.
Rosemarie
R
Haberle
Department of Plant Sciences, MS2, University of California Davis, Davis, California, 95616, United States of America.
Daniel
D
Potter
College of Life Sciences, Northwest A&F University, Yangling, Shaanxi, 712100, China.
Zhao-Yang
ZY
Chang
Department of Botany, National Museum of Natural History, MRC 166, Smithsonian Institution, Washington, DC, 20013-7012, United States of America.
Jun
J
Wen
D002467:Cell Nucleus / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D019143:Evolution, Molecular; D017343:Genes, Plant; D010802:Phylogeny; D018087:Plastids / Q000235:genetics; D011123:Polyploidy; D027861:Prunus / Q000145:classification / Q000166:cytology / Q000235:genetics*
D018744:DNA, Plant