The mechanism of tetraploidization in tree peony, and its implications for speciation and evolution of genus L.

INTRODUCTION

Polyploidization is not only an important driving force for plant speciation and evolution, but also an effective approach for plant domestication and improvement. Polyploid taxa are quite common in section (herbaceous peonies), but very rare in section (tree peonies), which are known as the 'king of flowers'.

METHODS

In this paper, we studied the origination of a tetraploid tree peony, 'Golden Era' ('GE', AABB), by comparing its karyotype with its seed parent, 'Golden Isles' ('GI', AB), based on genomic hybridization (GISH) and rDNA fluorescence hybridization (FISH). The meiosis behaviors of 'GI' were observed to make clear the cytogenetic process of unreduced (2) gamete generation.

RESULTS

Four chromosomes with inter-genome translocations were identified in 'GE', two of which might be reciprocal translocations. The 2 female gametes first division restitution (FDR) from 'GI' might play an important role in tetraploidization of 'GE'.

DISUCSSION

The distant hybridization between intersterile species from different subsections of section probably promotes the tetraploidization of tree peonies by facilitating 2 gamete production. The mechanism of tetraploidization in section is highly consistent with that in section , but is inseparable with the assist from mankind. The divergence of life history between tree peonies and herbaceous peonies is speculated to contribute to the different level of polyploidization, and distinct tempo of speciation and evolution, between section and section in genus . These findings bring new insights to polyploid breeding, speciation and evolution in genus .