Cytoplasmic and Genomic Effects on Meiotic Pairing in Brassica Hybrids and Allotetraploids from Pair Crosses of Three Cultivated Diploids

Abstract

Interspecific hybridization and allopolyploidization contribute to the origin of many important crops. Synthetic Brassica is a widely used model for the study of genetic recombination and "fixed heterosis" in allopolyploids. To investigate the effects of the cytoplasm and genome combinations on meiotic recombination, we produced digenomic diploid and triploid hybrids and trigenomic triploid hybrids from the reciprocal crosses of three Brassica diploids (B. rapa, AA; B. nigra, BB; B. oleracea, CC). The chromosomes in the resultant hybrids were doubled to obtain three allotetraploids (B. juncea, AA.BB; B. napus, AA.CC; B. carinata, BB.CC). Intra-and intergenomic chromosome pairings in these hybrids were quantified using genomic in situ hybridization and BAC-FISH. The level of intra-and intergenomic pairings varied significantly, depending on the genome combinations and the cytoplasmic background and/or their interaction. The extent of intragenomic pairing was less than that of intergenomic pairing within each genome. The extent of pairing variations within the B genome was less than that within the A and C genomes, each of which had a similar extent of pairing. Synthetic allotetraploids exhibited nondiploidized meiotic behavior, and their chromosomal instabilities were correlated with the relationship of the genomes and cytoplasmic background. Our results highlight the specific roles of the cytoplasm and genome to the chromosomal behaviors of hybrids and allopolyploids.

The effect of different genome and cytoplasm on meiotic pairing in maize newly synthetic polyploids

“…Similar phenomenon is observed in synthetic brassica hybrids, comparing with A and C genome, B genome has more stable and less pairing variation (Cui et al 2012). But for Brassica allotetraploids, which have highly differentiated cytoplasm, the genome coming from the male parent was significantly modified, compared to the genome coming from the female parent (Song et al 1995), and other experimental results obtain the same conclusion (Cui et al 2012). A possible explanation is that the maternal enzymatic system may treat the male chromosomes as exogenous intruder (Wang et al 2010;Hu et al 2013).…”

“…During wheat polyploidization process, the genome tends to lose specific low copy sequences from D genome, which shows parental tendency and inherent difference of parent genome stability (Ozkan et al 2001). Similar phenomenon is observed in synthetic brassica hybrids, comparing with A and C genome, B genome has more stable and less pairing variation (Cui et al 2012). But for Brassica allotetraploids, which have highly differentiated cytoplasm, the genome coming from the male parent was significantly modified, compared to the genome coming from the female parent (Song et al 1995), and other experimental results obtain the same conclusion (Cui et al 2012).…”

“…In order to analyze the chromosome paring with overall level, the chromosome calculation formula of autosyndesis and allosyndesis were carried out referring to the method of Cheng Cui (Cui et al 2012) and modified slightly (Fig. 1).…”

“…The results suggest Z. perennis cytoplasm may give a relatively relaxed environment especially for maize genome. The possible reasons include: (a) the presence of foreign nuclear genome in cytoplasm from the male parent can result in nuclear-cytoplasm incompatibility (Wang et al 2010;Cui et al 2012) and maternal enzymatic system may treat the male chromosomes as exogenous intruders (Hu et al 2013), thus, gene structure variation, aneuploidy and chromosomes structure variation as well as meiosis confusion can potentially occur, comparing to Z. perennis cytoplasm, maize cytoplasm probably has a stronger defense system; (b) Z. perennis is more primitive than maize (Wang et al 2011), and the cytoplasm may have a greater containment than maize; (c) Z. perennis cytoplasm probably has a less negative influence on Phs1 and Pam1 than maize cytoplasm. Additional, interactions can occur between nuclear and cytoplasm followed by loss of genes from both nuclear genome and plasmon (Rand et al 2004), which suggests genome stability also may be affected by interactions between different genome composition and cytoplasm (Cui et al 2012), different results in allotriploids and allotetraploids conform to this speculation.…”

Extraction of the Constituent Subgenomes of the Natural Allopolyploid Rapeseed (Brassica napus L.)

“…Multiple target FISHs with these probes were performed to identify certain MAALs according to the work of Xiong and Pires (2011). Slide preparations were carried out mainly according to the methods of Zhong et al (1996) and the procedures of BAC-FISH analyses following the procedure of Cui et al (2012) with slight modification to reduce the washing time to 8 min in 0.1 3 SSC with 20% deionized formamide at 40°. Before a second round of FISH, slides were washed for 10 min in 2 3 SSC with 50% deionized formamide at 42°to clear former hybridized probe.…”