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Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

ABSTRACT: BACKGROUND AND AIMS:Is there selection minimizing the costs of ovule production? Such selection should lead to a smaller ovule size in relation to seed size and, at the same time, smaller variation in ovule size within plants, the latter because the minimum structures and resources for functioning of ovules should be the same among ovules. Additionally, within species, ovule size should not depend on the plant's resource status. METHODS:To confirm these predictions, we examined ovule and seed production for a variety of species. KEY RESULTS:Among the 27 species studied, we found a significant negative dependence of the species mean of the coefficient of variation for plant ovule size on the ratio of the mean species seed size/mean species ovule size. Thus, the smaller the ovule size as compared with seed size, the smaller the degree of variation in ovule size. Among the 49 species studied, only two species showed significant positive dependence of mean ovule size on plant size. Although larger plants should have greater resources for ovule production, selection has not enhanced the production of large ovules in most species. CONCLUSIONS:These results suggest that there is selection minimizing the costs of ovule production.

SUBMITTER: Itagaki T

PROVIDER: S-EPMC6612939 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

Itagaki Tomoyuki T Mochizuki Jun J Aoyagi Blue Yuta Y Ito Masaya M Sakai Satoki S

Annals of botany 20190701 7

<h4>Background and aims</h4>Is there selection minimizing the costs of ovule production? Such selection should lead to a smaller ovule size in relation to seed size and, at the same time, smaller variation in ovule size within plants, the latter because the minimum structures and resources for functioning of ovules should be the same among ovules. Additionally, within species, ovule size should not depend on the plant's resource status.<h4>Methods</h4>To confirm these predictions, we examined ov ...[more]

PMID: 30918957

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Project description:Some species of Genlisea possess ultrasmall nuclear genomes, the smallest known among angiosperms, and some have been found to have chromosomes of diminutive size, which may explain why chromosome numbers and karyotypes are not known for the majority of species of the genus. However, other members of the genus do not possess ultrasmall genomes, nor do most taxa studied in related genera of the family or order. This study therefore examined the evolution of genome sizes and chromosome numbers in Genlisea in a phylogenetic context. The correlations of genome size with chromosome number and size, with the phylogeny of the group and with growth forms and habitats were also examined.Nuclear genome sizes were measured from cultivated plant material for a comprehensive sampling of taxa, including nearly half of all species of Genlisea and representing all major lineages. Flow cytometric measurements were conducted in parallel in two laboratories in order to compare the consistency of different methods and controls. Chromosome counts were performed for the majority of taxa, comparing different staining techniques for the ultrasmall chromosomes.Genome sizes of 15 taxa of Genlisea are presented and interpreted in a phylogenetic context. A high degree of congruence was found between genome size distribution and the major phylogenetic lineages. Ultrasmall genomes with 1C values of <100 Mbp were almost exclusively found in a derived lineage of South American species. The ancestral haploid chromosome number was inferred to be n = 8. Chromosome numbers in Genlisea ranged from 2n = 2x = 16 to 2n = 4x = 32. Ascendant dysploid series (2n = 36, 38) are documented for three derived taxa. The different ploidy levels corresponded to the two subgenera, but were not directly correlated to differences in genome size; the three different karyotype ranges mirrored the different sections of the genus. The smallest known plant genomes were not found in G. margaretae, as previously reported, but in G. tuberosa (1C ? 61 Mbp) and some strains of G. aurea (1C ? 64 Mbp).Genlisea is an ideal candidate model organism for the understanding of genome reduction as the genus includes species with both relatively large (?1700 Mbp) and ultrasmall (?61 Mbp) genomes. This comparative, phylogeny-based analysis of genome sizes and karyotypes in Genlisea provides essential data for selection of suitable species for comparative whole-genome analyses, as well as for further studies on both the molecular and cytogenetic basis of genome reduction in plants.

Dataset Information

Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

Publications

Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

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