Intraspecific variation of genome size in Guaranís´s maize landraces: cytological and phenological correlates.

REALINI MARÍA FLORENCIA; POGGIO, LIDIA; GONZÁLEZ GRACIELA E.

Atibaia, San Pablo

Congreso; 4ª Reunión Brasileira de Citogenética y III SLACE; 2015

Sociedad Brasilera de Genética

Genome size varies among species and their diversification accompanies the evolution of many species. Several works focused in the phenotypic effects of genome size variations in plants and relationships between genome size and phenotype at the nuclear, cellular and whole plant levels. Zea is an interesting model to test several correlations among genome size and nuclear and environmental parameters, because it shows both intra- and interspecific variation in DNA amount. The variation in DNA content in maize has been proposed to be principally due to differences in the number and size of heterochromatic blocks, called knobs. But this variation also due to differences in the amount of interspersed DNA. In fact, LTR-retrotransposons makes up over 70 % of the nuclear maize genome. The knobs occur in all Zea species with 2n = 20 and have been observed in 34 distinct cytological locations varying in size and number across maize races and their wild relatives. These are composed primarily of two tandemly repeated sequences, the 180-bp knob repeat and TR-1 (350-bp). The fluorescent in situ hybridization (FISH) technique to map a variety of repeats DNA sequences has useful for karyotyping and chromosome identification. In Northeastern Argentina (NEA) up to 15 Guarani?s maize landraces maize can be found in indigenous settings from the subtropical forests of the Misiones Province. In the present work, we analyzed and correlated in maize Guarani?s landraces variation of genome size, cytological parameters and two phenotypic parameters (vegetative cycle and seed mass). To evaluate these, we used 18 populations of all Guarani?s maize landraces described from NEA. DNA amount estimated by flow cytometry varied from 4.62pg to 6.29pg. We confirmed that maize presented a wide intra-specific and even intra-population variation in the genome size. DAPI staining and FISH experiments, using 180-bp and TR-1 sequences as probes, was performed on 8 Guarani?s landraces, and detected that number (10-22), size, positions (17 different positions) and sequence Compositions were highly variable among studied landraces. Even though the studied populations presented variations on the seed mass, a significant correlation between seed mass and genome size was not found. Finally, while genome size and vegetative cycle not presented a significant correlation, the percentage of heterochromatin appeared more related to then. All these results suggest that heterochromatin could have adaptive value, influence phenotypic parameters such as vegetative cycle. This study is a contribution to the knowledge of the phenotypic and karyotype variability of argentine maize landraces.