Genome size and repetitive sequences are driven by artificial selection on the length of the vegetative cycle in maize landraces from Northeastern Argentina

Abstract

Variation in genome size and knob heterochromatin content was explored in relationship to altitudinal cline and length of the vegetative cycle in northern Argentina, USA and Mexico landraces. It was considering that the decrease in DNA and heterochromatin content could be an adaptation to a shorter growing season and the result of artificial selection by man. Guaraní landraces from Northeastern Argentina (NEA) show similar variation in genome size (3.81pg to 7.56pg) and knob heterochromatin content than maize growing across an altitudinal cline. The present analysis offers an overview of the genetic variability of NEA maize to explain why Guaraní landraces and those along an altitudinal cline share this similar variation. Karyotype and flow cytometry data were employed. The DNA content of Guaraní landraces which lacking B chromosomes, showed no significant relationship with knob heterochromatin, suggesting differences in the amount of interspersed DNA. A significant positive relationship was found between the length of the vegetative cycle and both number and percentage of knob heterochromatin. No significant correlation was found between genome size and vegetative cycle. All these results allow us to conclude that the variation in heterochromatin content among Guaraní maize is driven by the selection of farmers for flowering time.

Intragenomic Conflict between Knob Heterochromatin and B Chromosomes Is the Key to Understand Genome Size Variation along Altitudinal Clines in Maize

“…The positive relationships between heterochromatin percentage and A-DNA content and their negative correlations with cultivation altitude so far reported for all the studied landraces, suggest a mechanistic link among heterochromatin, genome size and phenology [ 9 , 10 , 11 , 20 ]. Realini et al [ 10 , 20 ], who studied maize populations from NEA, found that heterochromatin percentage is positively correlated with the length of the vegetative period. The authors interpreted the variation in heterochromatin percentage and DNA content as the result of artificial selection on flowering time.…”

“…Based on these results, it was postulated that genome downsizing would be associated with rapid vegetative growth and early flowering time. These characteristics are typical of populations adapted to shorter growing seasons in highland regions [8,15,[19][20][21][22]32]. Variation in total DNA content, comprising both genic and non-genic DNA (nucleotype [30]) affects cellular and developmental parameters.…”

“…This assumption is supported by evidence showing that the percentage of knob heterochromatin of the A-chromosome set (A-HC) is negatively correlated with cultivation altitude, but positively correlated with the vegetative period. Realini et al [ 10 , 20 ] found a positive correlation between the length of the vegetative cycle and A-HC in maize landraces from Northeastern Argentina (NEA). This relationship was also reported for maize populations from different localities [ 15 , 21 , 22 ].…”

“…This relationship was also reported for maize populations from different localities [ 15 , 21 , 22 ]. The length of the vegetative cycle was proposed to be optimized through artificial selection for an appropriate percentage of heterochromatin [ 10 , 15 , 20 ].…”

Chromosomic Studies in Zephyranthes Citrina Baker (Amaryllidaceae), a Polyploid Ornamental

“…Our research group has carried out numerous cytogenetic studies on Zea species, mainly focused on native Argentinian and Bolivian maize landraces (Tito et al, 1991;Quintela Fernández et al, 1995;Poggio et al, 1998Poggio et al, , 1999aPoggio et al, , 1999bPoggio et al, , 2000aPoggio et al, , 2000bPoggio et al, , 2005Rosato et al, 1998;González et al, 2004González et al, , 2006González et al, , 2013González and Poggio, 2011Realini et al, 2016Realini et al, , 2018Realini et al, , 2021Fourastié et al, 2017;Poggio and González, 2018).…”