Cytological diploidization in the paleopolyploid genus Zea

POGGIO LIDIA; GONZÁLEZ, GRACIELA

Atibaia, San Pablo

Congreso; IV Reunión Brasilera de Citogenética; 2015

Sociedad Brasilera de Genética

Cytological diploidization in the paleopolyploid genus Zea   Poggio L1, González GE1   1 Laboratorio de Citogenética y Evolución ? Departamento de Ecología Genética y Evolución ? Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires ? IEGEBA (CONICET ? UBA) ? Intendente Gúiraldes 2160 ?C1428EGA CABA, Argentina.   Zea, a paleopolyploid complex, is an interesting model to analyze the cytological diploidization, the process by which polyploidy leads to chromosomically and genetically balanced gametes. This process is fundamentally different in autopolyploid and allopolyploid species, because of their chromosome composition. Maize and its allied wild relatives (species of teosintes) with 2n=20 are segmental allotetraploids (AxAxBxBx), while Z. perennis (2n= 40) is an autoallooctoploid (ApApApApBp1B p1Bp2B p2). In previous studies we applied dilute colchicine solution (0.5mM) at the onset of meiosis in maize and Z. perennis and proposed that colchicine suppress the expression of a maize locus equivalent to the Ph of wheat. These  studies demonstrated that in maize, a tetraploid that have evolved 11 million year ago, homoeologous pairing still occur when it is treated with colchicine. In the present work we analyze the amount of chromosome pairing at MI in hybrids between tetraploid species and Z. perennis. In untreated (UT) individuals of Z. perennis the most frequent configuration was 5 IV + 10 II (formed by A genomes and B genomes, respectively). The colchicine treated material show up to 10 IV indicating higher affinity within genomes A and B, but any homology among them. Hexaploid hybrids between 2n=20 and 2n=40 teosintes species (ApApAxBp1Bp2Bx), with only one doses of Ax, Bx, Bp1 and Bp2 genomes, showed at meiosis of UT individuals 5III+5II+5I. In treated material they showed up to 10 III, indicating greater homology among B genomes than that estimated in UT material. The hexaploid hybrid Z. perennis x Z. mays presented more frequently 5III+5II+5I in UT individuals. Instead, individuals treated with colchicine 0.5mM showed VI, IV and III. This unexpected result differs from that observed in other 6x teosintes hybrids and could be explained if A and B genomes of maize were homeologous. In Zea mays ssp. mays treated with higher dosis of colchicine (1mM) total asynapsis and homologous separation was observed. This result resembles that obtained in wheat, where high doses of colchicine have the same effect of extra doses of Ph gene. The presented data led us to postulate a pairing regulator gene system in the genus Zea (PRZ), which would be related with the threshold of homology and dosage of ploidy level. Besides the presence of a genetic control that precludes pairing between homoeologous, the cytological diploidization in the genus Zea could be achieved by processes that increase the differentiation of homoeologous chromosomes.