CAUSES AND CONSEQUENCES OF DNA CONTENT VARIATION IN ZEA

GONZÁLEZ, G.E.; REALINI, M.F.; FOURASTIÉ, M.F.; POGGIO, L.

Basic and Applied Genetics

SOCIEDAD ARGENTINA DE GENÉTICA

Año: 2022 vol. 33 p. 43 - 49

1666-0390

Cytogenetic evidence indicates that Zea, which comprises maize (Z. mays ssp. mays) and its wildrelatives, is an allopolyploid genus. Our research group has carried out numerous cytogeneticstudies on Zea species, mainly focused on native Argentinian and Bolivian maize landraces. Wefound a wide inter- and intraspecific genome size variation in the genus, with mean 2C-valuesranging between 4.20 and 11.36 pg. For the maize landraces studied here, it varied between 4.20and 6.75 pg. The objectives of this work are to analyze the causes of genome size variation andto discuss their adaptive value in Zea. This variation is mainly attributed to differences in theheterochromatin located in the knobs and to the amount of interspersed DNA from retrotransposons.Polymorphisms in presence or absence of B-chromosomes (Bs) and the population frequency ofBs are also a source of genome size variation, with doses ranging between one and eight in thelandraces analyzed here. Correlation analysis revealed that the percentage of heterochromatinis positively correlated with genome size. In addition, populations cultivated at higher altitudes,which are known to be precocious, have smaller genome sizes than do those growing at loweraltitudes. This information, together with the positive correlation observed between the lengthof the vegetative cycle and the percentage of heterochromatin, led us to propose that it has anadaptive role. On the other hand, the negative relationship found between Bs and heterochromaticknobs allowed us to propose the existence of an intragenomic conflict between these elements. Wehypothesize that an optimal nucleotype may have resulted from such intranuclear conflict, wheregenome adjustments led to a suitable length of the vegetative cycle for maize landraces growingacross altitudinal clines.