Meiotic Chromosome Stability and Suppression of Crossover Between Non-homologous Chromosomes in x Brassicoraphanus, an Intergeneric Allotetraploid Derived From a Cross Between Brassica rapa and Raphanus sativus

Hye Rang Park; Jeong Eun Park; Jung Hyo Kim; Hosub Shin; Seung Hwa Yu; Sehyeok Son; Gibum Yi; Soo-Seong Lee; Hyun Hee Kim; Jin Hoe Huh

doi:10.3389/fpls.2020.00851

Meiotic Chromosome Stability and Suppression of Crossover Between Non-homologous Chromosomes in x Brassicoraphanus, an Intergeneric Allotetraploid Derived From a Cross Between Brassica rapa and Raphanus sativus

Front Plant Sci. 2020 Jun 16:11:851. doi: 10.3389/fpls.2020.00851. eCollection 2020.

Authors

Hye Rang Park¹, Jeong Eun Park¹, Jung Hyo Kim^{1

2}, Hosub Shin¹, Seung Hwa Yu^{1

2}, Sehyeok Son¹, Gibum Yi^{1

3}, Soo-Seong Lee⁴, Hyun Hee Kim⁵, Jin Hoe Huh^{1

2

3

6}

Affiliations

¹ Department of Plant Science, Seoul National University, Seoul, South Korea.
² Interdisciplinary Program in Agricultural Genomics, Seoul National University, Seoul, South Korea.
³ Plant Genomics and Breeding Institute, Seoul National University, Seoul, South Korea.
⁴ BioBreeding Institute, Ansung, South Korea.
⁵ Department of Life Science, Chromosome Research Institute, Sahmyook University, Seoul, South Korea.
⁶ Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, South Korea.

Abstract

Hybridization and polyploidization are major driving forces in plant evolution. Allopolyploids can be occasionally formed from a cross between distantly related species but often suffer from chromosome instability and infertility. xBrassicoraphanus is an intergeneric allotetraploid (AARR; 2n = 38) derived from a cross between Brassica rapa (AA; 2n = 20) and Raphanus sativus (RR; 2n = 18). xBrassicoraphanus is fertile and genetically stable, while retaining complete sets of both B. rapa and R. sativus chromosomes. Precise control of meiotic recombination is essential for the production of balanced gametes, and crossovers (COs) must occur exclusively between homologous chromosomes. Many interspecific hybrids have problems with meiotic division at early generations, in which interactions between non-homologous chromosomes often bring about aneuploidy and unbalanced gamete formation. We analyzed meiotic chromosome behaviors in pollen mother cells (PMCs) of allotetraploid and allodiploid F1 individuals of newly synthesized xBrassicoraphanus. Allotetraploid xBrassicoraphanus PMCs showed a normal diploid-like meiotic behavior. By contrast, allodiploid xBrassicoraphanus PMCs displayed abnormal segregation of chromosomes mainly due to the absence of homologous pairs. Notably, during early stages of meiosis I many of allodiploid xBrassicoraphanus chromosomes behave independently with few interactions between B. rapa and R. sativus chromosomes, forming many univalent chromosomes before segregation. Chromosomes were randomly assorted at later stages of meiosis, and tetrads with unequal numbers of chromosomes were formed at completion of meiosis. Immunolocalization of HEI10 protein mediating meiotic recombination revealed that COs were more frequent in synthetic allotetraploid xBrassicoraphanus than in allodiploid, but less than in the stabilized line. These findings suggest that structural dissimilarity between B. rapa and R. sativus chromosomes prevents non-homologous interactions between the parental chromosomes in allotetraploid xBrassicoraphanus, allowing normal diploid-like meiosis when homologous pairing partners are present. This study also suggests that CO suppression between non-homologous chromosomes is required for correct meiotic progression in newly synthesized allopolyploids, which is important for the formation of viable gametes and reproductive success in the hybrid progeny.

Keywords: hybrids; intergeneric hybridization; meiosis; polyploidy; synapsis.