Abstract
Cytogenetic evidence indicates that Zea, which comprises maize (Z. mays ssp. mays) and its wild relatives, is an allopolyploid genus. Our research group has carried out numerous cytogenetic studies on Zea species, mainly focused on native Argentinian and Bolivian maize landraces. We found a wide inter- and intraspecific genome size variation in the genus, with mean 2C-values ranging between 4.20 and 11.36 pg. For the maize landraces studied here, it varied between 4.20 and 6.75 pg. The objectives of this work are to analyze the causes of genome size variation and to discuss their adaptive value in Zea. This variation is mainly attributed to differences in the heterochromatin 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 of Bs are also a source of genome size variation, with doses ranging between one and eight in the landraces analyzed here. Correlation analysis revealed that the percentage of heterochromatin is 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 lower altitudes. This information, together with the positive correlation observed between the length of the vegetative cycle and the percentage of heterochromatin, led us to propose that it has an adaptive role. On the other hand, the negative relationship found between Bs and heterochromatic knobs allowed us to propose the existence of an intragenomic conflict between these elements. We hypothesize that an optimal nucleotype may have resulted from such intranuclear conflict, where genome adjustments led to a suitable length of the vegetative cycle for maize landraces growing across altitudinal clines. Key words: B chromosomes, heterochromatin, intragenomic conflict, knobs, maize landraces
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Claims 11
Claim · model-written summary
Zea species varied in genome size, with mean 2C-values of 4.20 to 11.36 pg.
ZeaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found a wide inter- and intraspecific genome size variation in the genus, with mean 2C-values ranging between 4.20 and 11.36 pg.”
t0“ZEA”
Claim · model-written summary
Genome size in the maize landraces varied from 4.20 to 6.75 pg.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For the maize landraces studied here, it varied between 4.20 and 6.75 pg.”
Claim · model-written summary
Differences in knob heterochromatin and retrotransposon DNA were attributed as the main sources of genome size variation in Zea.
- Outcome
- This variatione0
- Qualifier
- differences in the heterochromatin located in the knobs and to the amount of interspersed DNA from retrotransposonse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This variation is mainly attributed to differences in the heterochromatin located in the knobs and to the amount of interspersed DNA from retrotransposons.”
t0“ZEA”
Claim · model-written summary
B-chromosome presence and frequency contributed to genome size variation in maize landraces, with doses from one to eight.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Polymorphisms in presence or absence of B-chromosomes (Bs) and the population frequency of Bs are also a source of genome size variation, with doses ranging between one and eight in the landraces analyzed here.”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
Heterochromatin percentage was positively correlated with genome size in Zea.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Correlation analysis revealed that the percentage of heterochromatin is positively correlated with genome size.”
t0“ZEA”
Claim · model-written summary
Maize populations at higher altitudes had smaller genomes than those at lower altitudes.
- Outcome
- genome sizese0
- Direction
- smallere0
- Comparator
- those growing at lower altitudese0
- Setting
- higher altitudese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“populations cultivated at higher altitudes, which are known to be precocious, have smaller genome sizes than do those growing at lower altitudes.”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
Vegetative cycle length was positively correlated with heterochromatin percentage in maize landraces.
- Outcome
- length of the vegetative cyclee0
- Direction
- positive correlatione0
- Comparator
- percentage of heterochromatine0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the positive correlation observed between the length of the vegetative cycle and the percentage of heterochromatin”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
B chromosomes and heterochromatic knobs had a negative relationship in maize landraces.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the negative relationship found between Bs and heterochromatic knobs”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
The authors proposed that heterochromatin has an adaptive role in maize landraces.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the percentage of heterochromatin, led us to propose that it has an adaptive role.”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
The authors proposed intragenomic conflict between B chromosomes and heterochromatic knobs in maize landraces.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the negative relationship found between Bs and heterochromatic knobs allowed us to propose the existence of an intragenomic conflict between these elements.”
e1“native Argentinian and Bolivian maize landraces”
Claim · model-written summary
The authors hypothesized that intranuclear conflict produced an optimal nucleotype that adjusted the vegetative cycle of maize landraces across altitude.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We hypothesize that an optimal nucleotype may have resulted from such intranuclear conflict, where genome adjustments led to a suitable length of the vegetative cycle for maize landraces growing across altitudinal clines.”