The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis

Abstract

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.

Genomic affinities between maize and Zea perennis using classical and molecular cytogenetic methods (GISH–FISH)

“…Moreover, these meiotic configurations detect chromosomal rearrangements that may act as reproductive isolation mechanisms. When we did this type of analysis on Zea species, and on artificial hybrids between species with equal and different ploidy levels, we could deduce their polyploid nature and the genomic formulae of all species (Poggio et al 2005). Accordingly, two different genomes were postulated to occur in these cryptic polyploids, each with x = 5 chromosomes, which were arbitrarily named FA_ and FB_.…”

“…Studies of interspecific hybrids with 2n = 30 chromosomes were especially important, as they provided strong cytogenetic evidence that x = 5 is the basic number of these species, thus confirming the cryptic polyploid nature of the genus , Poggio & Naranjo 1995. Based on analyses of meiotic behaviour in parental species and hybrids, we developed genomic formulae that denote the genomic composition of each species (Poggio et al 2005). It was thereby established unequivocally for the first time that the extant n = 10 genomes of Zea mays ssp.…”

Nuclear Architecture and Chromatin Dynamics in Interphase Nuclei of <b><i>Arabidopsis thaliana</i></b>

“…Interstitial blocks of heterochromatin, called knobs, occur on the chromosome arms of maize and related species [Poggio et al, 2005;Albert et al, 2010]. Knobs vary in size and composition but are highly enriched in DNA repeats and TEs.…”

Chromosome numbers in plant cytotaxonomy: concepts and implications

“…Indeed, the n = 5 genome of A. thaliana seems to be derived from a paleopolyploid n = 8 karyotype found in several genera of Brassicaceae (Yogeeswaran et al, 2005), whereas Z. mays n = 10 is not a diploid with x = 10 but a tetraploid derived from ancestors with x = 5 (Gaut et al, 2000;Poggio et al, 2005). However, it should be emphasized that genome diploidization does not imply chromosome number reduction, as the name 'diploidization' and the example of A. thaliana may suggest.…”