Cecilia I. Comas

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

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)

In this study we have analysed and compared the genomic composition, meiotic behaviour, and meiotic affinities of Zea perennis and Zea mays ssp. mays. To do so we studied the parental taxa and the interspecific hybrid Zea perennis × Zea mays ssp. mays, using classical cytogenetic methods, as well as GISH and FISH. GISH enabled us to recognize the genomic source of each chromosome involved in the meiotic configurations of this hybrid, and established the genomic affinities between their parental species. The results obtained here reinforce the hypothesis of the amphiploid origin of Zea perennis and, together with previous research, indicate that the chromosomes with divergent repetitive sequences in maize and Zea luxurians could be the remnants of a relict parental genome not shared with Zea perennis.

Evolutionary relationships in the genus Zea: analysis of repetitive sequences used as cytological FISH and GISH markers

The present study is a revision of our work on evolutionary cytogenetics of the genus Zea, including several new experiments which give a deeper insight into the nature of the DNA sequences involved in telomeric regions of Zea luxurians. These new experiments, based on the Southern blotting technique and in situ hybridization, have demonstrated the following: 1) in situ hybridization (FISH) demonstrated the presence of the 180-bp repeat maize-knob-repeat-sequence in DAPI-positive terminal heterochromatic blocks of Z. luxurians (ZL-THB region); 2) Southern blot analysis confirmed that the 180-bp repeat present in maize is also present in Z. diploperennis, Z. luxurians and Tripsacum dactyloides, but not in Z. perennis; 3) another sequence with targeted sites for endonucleases, but without recognition sites for the 180-bp repeat, may be interspersed with the 180-bp repeat in a tandem array sited in the ZL-THB region; 4) in situ hybridization (GISH) of probes and blocking-probes with chromosomes of Z. luxurians (using Z. luxurians as a probe and Z. diploperennis or Z. perennis as a blocking-probe) gave strong fluorescence in both cases. Since Z. diploperennis possesses the 180-bp repeat, fluorescence on Z. luxurians chromosomes was not expected. These results can be explained if the ZL-THB regions are composed not only of 180-bp repeats interspersed with other sequences, but also of other tandem arrays unique to Z. luxurians, which, according to our GISH results, are probably located at the subterminal position.

Species relationships in Bulnesia as shown by seed protein electrophoresis

Abstract The seed proteins of seven species of Bulnesia were studied by polyacrylamide electrophoresis. Some of the bands are characteristic and constant “markers” of each species; these allow the unequivocal identification of their electrophoregrams. In total 84 different bands were identified. These were treated numerically by cluster analysis. There were no constant differences between geographic races of B. arborea from Colombia and Venezuela. The electrophoregram of B. carrapo shows differences with that of B. arborea giving support to the idea that both taxa are separate allopatric species. The species pair B. foliosa-B. schickendantzii present the most similar electrophoregrams; this determines a short taxonomic distance between them in the phenogram. The Prim network shows the supposedly more primitive species ( B. arborea, B. carrapo and B. bonariensis ) well separated from the more advanced group ( B. schickendantzii, B. foliosa and B. retama ). B. sarmientoi , however, appears as rather distant and unrelated from all other taxa. In general, the results from protein electrophoresis agree with results from a previous numerical study based on 43 morphological characters.

THE GENUS BULNESIA REVISITED : A CLADISTIC ANALYSIS OF SEED PROTEIN DATA

Bulnesia (Zygophyllaceae) is a South American genus consisting of nine species distributed into two subgenera: Gonopterodendron and Bulnesia. Cladistic analyses of the genus was performed using 90 characters from seed protein electrophoresis. Fourteen most parsimonious cladograms were generated with 26 steps and a very high consistency index of 0.95. Out of the 90 bands analyzed, 8 were informative characters because they did not represent autoapomorphies or genus synapomorphies. Out of the 14 cladograms obtained, two had a topology that support the genus subdivision previously inferred by systematic studies based on morphologic, cytogenetic and other biochemical characters. The evolutionary relationships among species are briefly discussed.

Isozyme variation inBulnesia retama, B. schickendantzii andB. foliosa (Zygophyllaceae)

The genetic variation between two allopatric populations ofBulnesia retama and that ofB. schickendantzii andB. foliosa was investigated. The Peruvian population ofB. retama showed low values of P (0.117) and He (0.057) compared to those in the Argentine population with P = 0.59 and He = 0.269;B. schickendantzii showed P = 0.54 andB. foliosa P = 0.17. Genetic identity between the latter was 0.836 and between the allopatric populations ofB. retama was 0.89; the Peruvian population had reduced allelic variation per locus (A = 1.176) in comparison to the Argentine population (A = 1.955). The values of A, P, He andWrights fixation indices suggest that the Peruvian population could have originated from a single or very few migrants from southern latitudes (founder effect).