Abstract
Genome size variation accompanies the diversification and evolution of many plant species. Relationships between DNA amount and phenotypic and cytological characteristics form the basis of most hypotheses that ascribe a biological role to genome size. The goal of the present research was to investigate the intra-specific variation in the DNA content in maize populations from Northeastern Argentina and further explore the relationship between genome size and the phenotypic traits seed weight and length of the vegetative cycle. Moreover, cytological parameters such as the percentage of heterochromatin as well as the number, position and sequence composition of knobs were analysed and their relationships with 2C DNA values were explored. The populations analysed presented significant differences in 2C DNA amount, from 4.62 to 6.29 pg, representing 36.15 % of the inter-populational variation. Moreover, intra-populational genome size variation was found, varying from 1.08 to 1.63-fold. The variation in the percentage of knob heterochromatin as well as in the number, chromosome position and sequence composition of the knobs was detected among and within the populations. Although a positive relationship between genome size and the percentage of heterochromatin was observed, a significant correlation was not found. This confirms that other non-coding repetitive DNA sequences are contributing to the genome size variation. A positive relationship between DNA amount and the seed weight has been reported in a large number of species, this relationship was not found in the populations studied here. The length of the vegetative cycle showed a positive correlation with the percentage of heterochromatin. This result allowed attributing an adaptive effect to heterochromatin since the length of this cycle would be optimized via selection for an appropriate percentage of heterochromatin.
Highlights
It is well known that genome size varies among species and their diversification accompanies the evolution of many groups of plants
Several studies demonstrated that there exists intra-specific and even intra-populational genome size variations
Significant intra-populational genome size variations were found, being 1.63-fold and 1.08-fold, the maximum and the minimum, variation detected among populations
Summary
It is well known that genome size varies among species and their diversification accompanies the evolution of many groups of plants In Zea, genome size is highly related to the inter- and intra-specific variations in the number and size of heterochromatic knobs (revisited in Poggio et al 1998) These knobs occur in all Zea species with 2n 1⁄4 20 and have been observed in 34 distinct cytological locations, varying in size and number across maize races and their wild relatives (Kato 1976; McClintock et al 1981; Tito et al 1991; Rosato et al 1998; Gonzalez and Poggio 2011; Gonzalez et al 2013). They are composed primarily of two tandem-repeated sequences, the 180-bp and TR-1, varying between a few thousand to millions of repeats (Peacock et al 1981; Ananiev et al 1998). 4′,6-Diamidino-2-phenylindole (DAPI) staining and fluorescent in situ hybridization (FISH) allowed us to reveal the chromosome location and the sequence composition of the knobs (Albert et al 2010; Gonzalez and Poggio 2011; Mondin et al 2014)
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