Revisiting the Hetero-Fertilization Phenomenon in Maize

Development of a seed DNA-based genotyping system for marker-assisted selection (MAS) has provided a novel opportunity for understanding aberrant reproductive phenomena such as hetero-fertilization (HF) by observing the mismatch of endosperm and leaf genotypes in monocot species. In contrast to conventional approaches using specific morphological markers, this approach can be used for any population derived from diverse parental genotypes. A large-scale experiment was implemented using seven F2 populations and four three-way cross populations, each with 534 to 1024 individuals. The frequency of HF within these populations ranged from 0.14% to 3.12%, with an average of 1.46%. The highest frequency of HF in both types of population was contributed by the pollen gametes. Using three-way crosses allowed, for the first time, detection of the HF contributed by maternal gametes, albeit at very low frequency (0.14%–0.65%). Four HF events identified from each of two F2 populations were tested and confirmed using 1032 single nucleotide polymorphic markers. This analysis indicated that only 50% of polymorphic markers can detect a known HF event, and thus the real HF frequency can be inferred by doubling the estimate obtained from using only one polymorphic marker. As expected, 99% of the HF events can be detected by using seven independent markers in combination. Although seed DNA-based analysis may wrongly predict plant genotypes due to the mismatch of endosperm and leaf DNA caused by HF, the relatively low HF frequencies revealed with diverse germplasm in this study indicates that the effect on the accuracy of MAS is limited. In addition, comparative endosperm and leaf DNA analysis of specific genetic stocks could be useful for revealing the relationships among various aberrant fertilization phenomena including haploidy and apomixis

Deciphering chemical order/disorder and material properties at the single-atom level

Correlating 3D arrangements of atoms and defects with material properties and functionality forms the core of several scientific disciplines. Here, we determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a model iron-platinum nanoparticle system to correlate 3D atomic arrangements and chemical order/disorder with material properties at the single-atom level. We identified rich structural variety and chemical order/disorder including 3D atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show for the first time that experimentally measured 3D atomic coordinates and chemical species with 22 pm precision can be used as direct input for first-principles calculations of material properties such as atomic magnetic moments and local magnetocrystalline anisotropy. This work not only opens the door to determining 3D atomic arrangements and chemical order/disorder of a wide range of nanostructured materials with high precision, but also will transform our understanding of structure-property relationships at the most fundamental level.Comment: 21 pages, 4 figure

Theoretical expectation for population sizes required for detection of HF events at various expected HF frequencies.

<p>Sample sizes required were calculated for each expected HF frequency to ensure to detect HF events at probability levels of 0.90, 0.95 and 0.99, respectively.</p

Probability of a marker confirming a hetero-fertility event.

<p>*The number of markers that are expected to be polymorphic was estimated using the averaged polymorphism rate (36.3%) as revealed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016101#pone.0016101-Yan1" target="_blank">[16]</a> using the same SNP chip for genotyping.</p

A diagram showing the probability for an HF event to be detected by using one polymorphic marker.

<p>For a given HF event and a given segregating marker locus within a population, two independent sperm cells derived from two different pollen grains, represented by H (triangle) and h (circle), respectively, can be only detected, with the probability of 50% (A), when the two pollen grains carry different alleles. However, when the two pollen grains carry the same allele (either H or h), the HF event is not detectable. The chance for the two pollen grains to carry the same H (B) or h (C) is 25%.</p

Hetero-fertilization event detected in F₂ populations.

<p>Genotype difference between endosperm DNA (E) and embryo DNA (L) can be revealed by one polymorphic SSR marker as shown by the arrow.</p

Detection of hetero-fertilization event contributed by different pollen grains in three-way cross populations.

<p>An HF plant in HP10 was detected as shown by the arrow. E: endosperm, L: leaf; A, B and C: three alleles derived from three different parents in the cross model (A×B)×C.</p

Hetero-fertilization frequencies as detected by one or two markers in seven F₂ populations.

<p>Note: The pollination model for five F₂ populations is A×B, where A is used as female parent and B as male parent. For consistency, the genotypes of SSR allele combination in endosperm (E) and leaf (L) are shown using the same symbol with the pollination model A and B.</p