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

Abstract

Cytological diploidization process is different in autopolyploid and allopolyploid species. Colchicine applied at the onset of meiosis suppresses the effect of pairing regulator genes resulting multivalents formation in bivalent-forming species. Colchicine treated maizes (4x = 2n = 20, AmAmBmBm) showed up to 5IV, suggesting pairing between chromosomes from genomes homoeologous Am and Bm. In untreated individuals of the alloautooctoploid Zea perennis (8x = 2n = 40, ApApAp´Ap´Bp1Bp1Bp2Bp2) the most frequent configuration was 5IV+10II (formed by A and B genomes, respectively). The colchicine treated Z. perennis show up to 10IV revealing higher affinity within genomes A and B, but any homology among them. These results suggest the presence of a paring regulator locus (PrZ) in maize and Z. perennis, whose expression is suppressed by colchicine. It could be postulated that in Z. perennis, PrZ would affect independently the genomes A and B, being relevant the threshold of homology, the fidelity of pairing in each genomes and the ploidy level. Cytological analysis of the treated hexaploid hybrids (6x = 2n = 30), with Z. perennis as a parental, strongly suggests that PrZ is less effective in only one doses. This conclusion was reinforced by the homoeologous pairing observed in untreated dihaploid maizes, which showed up to 5II. Meiotic behaviour of individuals treated with different doses of colchicine allowed to postulate that PrZ affect the homoeologous association by controlling entire genomes (Am or Bm) rather than individual chromosomes. Based on cytological and statistical results it is possible to propose that the cytological diploidization in Zea species occurs by restriction of pairing between homoeologous chromosomes or by genetical divergence of the homoeologous chromosomes, as was observed in untreated Z. mays ssp. parviglumis. These are independent but complementary systems and could be acting jointly in the same nucleus.

Genomic and Meiotic Changes Accompanying Polyploidization

“…In the Zea genus, which includes allotetraploid species with 2n = 20 chromosomes, such as maize, Zea mays L., and teosintes, and the alloautooctoploid species Z. perennis (2n = 40), a paring regulator locus ( PrZ ), whose expression is suppressed by colchicine, has been recently reported [ 204 ]. Poggio and González postulated that, in Z. perennis , PrZ would affect independently the A and B maize genomes, being relevant the threshold of homology, the fidelity of pairing in each genomes and the ploidy level [ 204 ]. To the best of our knowledge, no other genes related to maize cytological diploidization have been described so far.…”

Multi-species polyploidization, chromosome shuffling, and genome extraction inZea/Tripsacumhybrids

“…There is no evidence of highly rearranged genomes being selected during the establishment of polyploid species. Recently, a pairing regulator locus PrZ has been reported in maize x Z. perennis hybrids (Poggio and González 2018), which may control homoeologous pairing or selection culled the plant with aberrant phenotypes and low fertility in early generations and favored only those plants which have stable chromosome numbers and rDNA loci, better pairing control, and advantageous chromosomes rearrangements. The nascent allotetraploids were propagated and maintained for up to 7 generations by self-breeding, regardless of pollen viability and genome stability, which showed plants with highly unstable and aberrant phenotypes could not survive.…”

Chromosomic Studies in Zephyranthes Citrina Baker (Amaryllidaceae), a Polyploid Ornamental

“…In the pioneering studies of Anderson (1945) maize was considered as allotetraploid 2n=4x=20, derived from extinct ancestors with 2n=10. Meiotic studies of intraand interspecific hybrids confirmed their allopolyploid nature, indicating that maize and its wild relatives are tetraploids, except for the octoploid Z. perennis, with x=5 being the basic chromosome number (revisited in Poggio et al, 2005;Poggio and González, 2018). Further molecular studies provided compelling evidence for the allopolyploid nature of maize (Moore et al, 1995;Gaut and Doebley, 1997;White and Doebley, 1998;Swigonova et al, 2004).…”

“…Our research group has carried out numerous cytogenetic studies on Zea species, mainly focused on native Argentinian and Bolivian maize landraces (Tito et al, 1991;Quintela Fernández et al, 1995;Poggio et al, 1998Poggio et al, , 1999aPoggio et al, , 1999bPoggio et al, , 2000aPoggio et al, , 2000bPoggio et al, , 2005Rosato et al, 1998;González et al, 2004González et al, , 2006González et al, , 2013González and Poggio, 2011Realini et al, 2016Realini et al, , 2018Realini et al, , 2021Fourastié et al, 2017;Poggio and González, 2018).…”