A CENH3 mutation promotes meiotic exit and restores fertility in SMG7-deficient Arabidopsis

Meiosis in angiosperm plants is followed by mitotic divisions to form multicellular haploid gametophytes. Termination of meiosis and transition to gametophytic development is, in Arabidopsis, governed by a dedicated mechanism that involves SMG7 and TDM1 proteins. Mutants carrying the smg7-6 allele are semi-fertile due to reduced pollen production. We found that instead of forming tetrads, smg7-6 pollen mother cells undergo multiple rounds of chromosome condensation and spindle assembly at the end of meiosis, resembling aberrant attempts to undergo additional meiotic divisions. A suppressor screen uncovered a mutation in centromeric histone H3 (CENH3) that increased fertility and promoted meiotic exit in smg7-6 plants. The mutation led to inefficient splicing of the CENH3 mRNA and a substantial decrease of CENH3, resulting in smaller centromeres. The reduced level of CENH3 delayed formation of the mitotic spindle but did not have an apparent effect on plant growth and development. We suggest that impaired spindle re-assembly at the end of meiosis limits aberrant divisions in smg7-6 plants and promotes formation of tetrads and viable pollen. Furthermore, the mutant with reduced level of CENH3 was very inefficient haploid inducer indicating that differences in centromere size is not the key determinant of centromere-mediated genome elimination.

DETERMINATION OF POLLEN VIABILITY AND GERMINATION RATIOS IN MERSIN ECOLOGY OF SOME EARLY APRICOT

Turkey is the leading country in the production of world apricots (Prunus armeniaca). In the country, apricots are usually grown for drying and fresh consumption, and apricots are also used for different purposes. This study was carried out to determine pollen viability and germination status in some foreign apricot varieties grown in Mut district of Mersin province, which has an important place in early ripening apricot production in Turkey. Pollen viability and germination ratios were determined by TTC and 1% agar 10% method in Mogador, Mikado, Pricia, Flopria apricot varieties. In terms of pollen values, the best result in terms of viable pollen is from the Mikado with 77.02% and Mogador varieties with 78.61%, while the Pricia variety with 44.09% in semi-viable pollen provides the most result, while Flopria and Pricia varieties produce the highest values in dead pollen results. In the germination tests, pollen germination rates were medium level in Flopria, Mogador and Mikado varieties the pollen germination rate of the Pricia variety is only 8.96%. The results obtained will be a guide in new orchard establishment and breeding studies.

Hybridization of Castor Bean (Ricinus communis L.) in Morelos, México

Objective: To determine the stigma receptivity and the pollen viability in order to make manual crosses and obtain viable progeny in castor bean (Ricinus communis L.).Design/Methodology/Approach: Pollen viability tests were made on breeding materials by staining with acetocarmine solution. In elite materials, the receptivity of the stigma was evaluated with hydrogen peroxide. From the inflorescences, the male ones were removed and the female ones were preserved, which were covered with a glassine bag. After six days, they were checked and when they were considered receptive, manual pollinations were carried out between viable pollen materials and receptive stigma. The pollen of the male parent was impregnated in the stigmas and the inflorescence was covered again.Results: The breeding materials exhibited viable pollen since they were stained red. Whereas, the application of hydrogen peroxide to the stigmas of the elite materials showed bubbling, indicative that they were receptive. In 2014, 400 inflorescences were pollinated with 8 flowers on average and a fruit pollinated percentage of 61.21. In 2015, 245 inflorescences with 12 flowers on average and 61.24% of fruit were pollinated.Study Limitations/Implications: Temperature and relative humidity were fundamental factors for the success of castor bean fertilization.Findings/Conclusions: The elite castor bean materials presented receptive stigmas and the improved viable pollen materials. Manual crosses produced fruits and seeds. The fruits pollinated were 61%.

A CENH3 mutation promotes meiotic exit and restores fertility in SMG7-deficient Arabidopsis

Meiosis in angiosperm plants is followed by mitotic divisions to form multicellular haploid gametophytes. Termination of meiosis and transition to gametophytic development is, in Arabidopsis, governed by a dedicated mechanism that involves SMG7 and TDM1 proteins. Mutants carrying the smg7-6 allele are semi-fertile due to reduced pollen production. We found that instead of forming tetrads, smg7-6 pollen mother cells undergo multiple rounds of chromosome condensation and spindle assembly at the end of meiosis, resembling aberrant attempts to undergo additional meiotic divisions. A suppressor screen uncovered a mutation in centromeric histone H3 (CENH3) that increased fertility and promoted meiotic exit in smg7-6 plants. The mutation led to inefficient splicing of the CENH3 mRNA and a substantial decrease of CENH3, resulting in smaller centromeres. The reduced level of CENH3 delayed formation of the mitotic spindle but did not have an apparent effect on plant growth and development. We suggest that impaired spindle re-assembly at the end of meiosis limits aberrant divisions in smg7-6 plants and promotes formation of tetrads and viable pollen. Furthermore, the reduced level of CENH3 did not induce haploid plants in crosses with wild plants, indicating that differences in centromere size is not the key determinant of centromere-mediate genome elimination.

Light promoted brown staining of protoplasm by Ag+ is ideal to test wheat pollen viability rapidly

Pollen viability is crucial for wheat breeding programs. The unique potential of the protoplasm of live cells to turn brown due to the synthesis of silver nanoparticles (AgNPs) through rapid photoreduction of Ag+, was exploited for testing wheat pollen viability. Ag+-viability test medium (consisting of 0.5 mM AgNO3 and 300 mM KNO3) incubated with wheat pollen turned brown within 2 min under intense light (~600 μmol photon flux density m-2s-1), but not in dark. The brown medium displayed AgNPs-specific surface plasmon resonance band in its absorption spectrum. Light microscopic studies showed the presence of uniformly stained brown protoplasm in viable pollen incubated with Ag+-viability medium in the presence of light. Investigations with transmission electron microscope coupled with energy dispersive X-ray established the presence of distinct 5–35 nm NPs composed of Ag. Powder X-ray diffraction analysis revealed that AgNPs were crystalline and biphasic composed of Ag0 and Ag2O. Conversely, non-viable pollen and heat-killed pollen did not turn brown on incubation with Ag+-medium in light. We believe that the viable wheat pollen turn brown rapidly by bio-transforming Ag+ to AgNPs through photoreduction. Our findings furnish a novel simplest and rapid method for testing wheat pollen viability.

Fertility and Progeny Ploidy of Triploids in China Rosa Germplasm

Background Although triploid plants are often assumed to be sterile, in Rosa, triploids appear to have been important in both species evolution and breeding. A better understanding of the fertility of China Rosa triploids and their behavior when used in interploidy crosses will not only improve gene introgression from China triploid roses to modern roses, but also enhance our understanding of male and female fertility mechanism with triploids. The objective of this study was to evaluate the usefulness of five triploid China roses for breeding by measuring the pollen size, quantifying the fertility and following the ploidy transmission of interploidy crosses. Results In the five triploids, the pollen grain size of Rosa multiflora var. cathayensis Rehd ‘Fen Tuan Qiang Wei’ followed a normal distribution, suggesting that 1 mainly ploidy level pollen grain were produced, while the pollen size of other 4 triploids followed skewed, flattened, and slightly bimodal distributions, indicating a wide range of chromosome numbers. Although none of the 5 triploids produced hips as females, 3 gave good hip and seed production on the tetraploid mother plant when used as the pollen parents. Based on the ploidy level analysis of their progeny, ‘Fen Tuan Qiang Wei’ produced 1n viable pollen whereas ‘Chun Shui Lü Bo’ and ‘Yu Shi Zhuang’ produced 2n viable pollen. In the meiosis of triploids, the triads, pentads and microcyte in the meiosis products indicated the objective triploid production of euploid pollen grains. Conclusions In this study we reported 1 China triploid rose produces 1n viable pollen, and 2 China triploid roses produce 2n viable pollen, and no anueploid progeny was produced. Our results indicate that the triploids contribute significantly to tetraploids formation in the crossing system of Genus Rosa, and it is possible for breeders to create novel rose types with valuable triploids in the future. With the special triploid resources found in this experiment, Genus Rosa will be an excellent material to study the mechanism of triploids in the future.

Pollen viability and fertility of species from genus Hemerocallis L.

The work presents the results of determining the pollen viability and fertility of three species from genusHemerocallis in the forest-steppe zone of Western Siberia. It was noted that H. middendorfii has the most viable pollen,while its value is quite low and amounts to only 5 %. In other species, the maximum value of this indicator varies from 1.9% (H. citrina) to 4.6 % (H. fulva). It was established that the pollen of studied species has a rather high degree of fertilityand takes values from 50.8–56.2 % of H. fulva to 93.4–95.7 % of H. middendorfii.

Selection based on meiotic behavior in Urochloa decumbens hybrids from non-shattered seed

This study aimed to evaluate the end-products of meiosis in sexual and apomictic hybrids of Urochloa decumbens, so as to identify genotypes with good production of viable pollen for use in breeding programs to increase yields of pure viable seed and reduce degree of seed shattering. From 457 intraspecific hybrids of U. decumbens arising from crosses between 3 artificially tetraploidized sexual plants and the apomictic cultivar Basilisk, 27 hybrids from non-shattered seed were selected. Slides were prepared by smearing anthers and staining to determine the presence of abnormalities. The abnormalities found were micronuclei, microcytes and polyads. The data were compared by the Scott-Knott test at P<0.05. Data obtained enabled separation of hybrids into 4 groups depending on the presence of micronuclei and formation of polyads and into 6 groups based on the presence of microcytes in the tetrads. Among the analyzed apomictic hybrids, R179 has the attributes for viable seed production to proceed to cultivar development. Among the sexual hybrids, R161, R181, R193 and S47 are recommended as female parents for use in crossing programs.

Characterization of Flowering Time and Pollen Production in Jojoba (Simmondsia chinensis) towards a Strategy for the Selection of Elite Male Genotypes

The seeds of the dioecious shrub jojoba (Simmondsia chinensis (Link) Schneider) yield a liquid wax that is in high demand for the cosmetics industry. While elite female cultivars of this species are currently clonally propagated, male plants are grown from seed, resulting in large variations in both the flowering period and the pollen viability, and hence large variation in yields. We characterized the existing male plant material in a local plantation as a platform for future selection of elite male cultivars that would produce sufficient amounts of viable pollen throughout the extended flowering period of the female cultivars. Using as a guide the number of viable pollen grains per 1-m branch, defined here as the calculated effective pollen productivity (EPP), we identified plants with an elevated EPP that flower concurrently with the female cultivars.