Variability in the amount of homoeologous pairing among F1 hybrids

Abstract

Genes involved in the exclusive pairing of homologous chromosomes have been described in several polyploid species but little is known about the activity of these genes in diploids (which have only one dose of each homoeologous genome). Analysis of the meiotic behaviour of species, natural and artificial hybrids and polyploids of Glandularia suggests that, in allopolyploids where homoeologous genomes are in two doses, regulator genes prevent homoeologous pairing. The different meiotic phenotypes in diploid F1 hybrids between Glandularia pulchella and Glandularia incisa strongly suggest that these pairing regulator genes possess an incomplete penetrance when homoeologous genomes are in only one dose. Moreover, the meiotic analysis of natural and artificial F1 hybrids suggests that the genetic constitution of parental species influences the activity of pairing regulator genes and is mainly responsible for variability in the amount of homoeologous pairing observed in diploid hybrids. In Glandularia, the pairing regulator genes originated in South American diploid species. The cytogenetic characteristics of this genus make it a good model to analyse and explore in greater depth the activity of pairing regulator genes at different ploidy levels.

Apospory and Diplospory in Diploid Boechera (Brassicaceae) May Facilitate Speciation by Recombination-Driven Apomixis-to-Sex Reversals

“…In this manner, apomixis may serve as an effective springboard in stabilizing reticulate evolution processes (Carman, 1997). Since allodiploidy increases rates of homoeologous recombination (Dewey, 1984; Wang, 1989; Grandont et al, 2014; Poggio et al, 2016), diploidization possibilities should be enhanced. Accordingly, the aposporous allodiploid Boechera identified herein are well suited for studying this putative speciation mechanism.…”

Cytological diploidization of paleopolyploid genus Zea: Divergence between homoeologous chromosomes or activity of pairing regulator genes?

“…napus (AACC) showed diploid-like meiotic behaviour, with only bivalents at MI, and pairing in dihaploids (AC) was also reported [ 1 , 6 ]. Incomplete dominance when homoeologous genomes are in only one dose was also reported in Glandularia [ 13 ].…”

“…This indicate that the PrZ -pairing regulator gene proposed for maize and Z . perennis is less efficient in dihaploid condition, as it was reported in dihaploids of Brassica and diploid hybrids of Glandularia [ 1 , 13 , 14 ]. Thus, all these results lead to postulated that PrZ preclude homoeologous pairing when homoeologous genomes are in two doses in the polyploids (B p1 B p1 B p2 B p2 ) but are inefficient when homoeologous genomes B p1 and B p2 are in one dose in the hybrids.…”

“…Interestingly, Feldman and Levy [ 8 ] showed that, in hexaploid wheat, each ancestral genome occupies a separate region in the nucleus, which in turn, is recognized by Ph1 . In polyploid species and hybrids of Glandularia , pairing regulator genes affecting the distance between nuclear site attachments of its two parental genomes was also proposed [ 13 ]. The studies carried out so far in different plants seem to indicate that different doses of pairing regulator genes affect the distance between nuclear site attachments of ancestral or parental homoeologous genomes of polyploid species [ 8 ].…”

“…There are evidences that this locus could contribute to the fidelity of synapses and crossover formation [ 6 , 8 – 12 ]. Ph1 -like genes were also postulated in other sexually propagating polyploids, such as Avena sativa , Festuca arundinacea , Brassica napus , Gossypium hirsutum and Gossypium barbadense , as well as in some diploids from genera Lolium and Glandularia [ 1 , 9 , 13 ].…”