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

POGGIO LIDIA; GONZALEZ GRACIELA

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2018

1932-6203

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 indicating higher affinity within genomes A and B, but any homology among them, then in maize and Z. perennis colchicine suppress the expression of a homeologous pairing regulator locus (PrZ). 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. The treated hexaploid hybrids with Z. perennis as a parental (6x=2n=30) reveal that PrZ is less effective in only one doses. This was also confirmed by the homeologous 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 genomes (Am or Bm) rather than individual chromosomes. The cytological diploidization in Zea species occurs by restriction of pairing between homoelogous chromosomes or by genetical divergence of the homeologous 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.