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.

Structure of Anther Epidermis and Endothecium, Production of Pollen, and Content of Selected Nutrients in Pollen Grains from Six Rubus idaeus L. Cultivars

Poland is the largest European Union producer of Rubus idaeus. This species provides insects with nectar and pollen from June to September. The rationale behind the present research is the increasing commercial production and the use of food attractants for pollinators increasing fruit yields. The intensive search for phytochemicals applicable in industry and phytotherapy together with the unavailability of data on anther epidermis and endothecium structure justify undertaking these investigations. The pollen mass, the content of elements, protein, and fat, as well as the composition of amino acids and fatty acids in the pollen of six R. idaeus cultivars were compared. In terms of pollen production, the cultivars ranked as follows: ’Pokusa’ < ‘Polana’ < ‘Glen Ample’ < ‘Polka’ < ‘Radziejowa’ < ‘Laszka’. The protein content (26–31%) in the pollen indicates its good quality and high attractiveness. Exogenous amino acids, including those with dietary importance, constituted a substantial proportion (33–39%). The content of MUFAs and PUFAs was 32–47% and 3.7–9.1%, respectively. The presence of elements that determine the nutritional value and proper development of pollen was detected in the mineral composition of the exine. The data on the epidermis and endothecium structure provide new information about the micromorphology, anatomy, ultrastructure of and generative organs and auxiliary criteria in the taxonomy of related species.

ATBS1-INTERACTING FACTOR 2 Negatively Modulates Pollen Production and Seed Formation in Arabidopsis

ATBS1-INTERACTING FACTOR 2 (AIF2) is a non-DNA-binding basic-helix-loop-helix (bHLH) transcription factor. Here, we demonstrate that AIF2 negatively modulates brassinosteroid (BR)-induced, BRASSINAZOLE RESISTANT 1 (BZR1)-mediated pollen and seed formation. AIF2-overexpressing Arabidopsis plants (AIF2ox) showed defective pollen grains and seed production while two AIF2 knockout mutants, aif2-1 and aif2-1/aif4-1, displayed opposite phenotypes. Genes encoding BZR1-regulated positive factors of seed size determination (SHB1, IKU1, MINI3) were suppressed in AIF2ox and genes for negative factors (AP2 and ARF2) were enhanced. Surprisingly, BZR1-regulated pollen genes such as SPL, MS1, and TDF1 were aberrantly up-regulated in AIF2ox plants. This stage-independent abnormal expression may lead to a retarded and defective progression of microsporogenesis, producing abnormal tetrad microspores and pollen grains with less-effective pollen tube germination. Auxin plays important roles in proper development of flower and seeds: genes for auxin biosynthesis such as TCPs and YUCCAs as well as for positive auxin signalling such as ARFs were suppressed in AIF2ox flowers. Moreover, lipid biosynthesis- and sucrose transport-related genes were repressed, resulting in impaired starch accumulation. Contrarily, sucrose and BR repressed ectopic accumulation of AIF2, thereby increasing silique length and the number of seeds. Taken together, we propose that AIF2 is negatively involved in pollen development and seed formation, and that sucrose- and BR-induced repression of AIF2 positively promotes pollen production and seed formation in Arabidopsis.

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.

Pollination efficiency of Apis mellifera (Hymenoptera: Apidae) on Cosmos sulphureus (Asteraceae) capitula at Dang (Ngaoundéré, Cameroon)

To study the foraging activity of Apis mellifera (Hymenoptera: Apidae) on Cosmos sulphureus (Asteraceae) and to evaluate its impact on fruits yields, C. sulphureus capitula were observed on Dang (Ngaoundéré, Cameroon) from September to November 2016 and from August to October 2017. Each year, observations were made every day, from 06.00 am to 6.00 pm on 540 capitula divided in four treatments: 120 capitula left in free polliniation, 120 capitula protected from insects ; 200 capitula protected, then uncovered, exclusively visited by A. mellifera and rebagged ; 100 capitula protected, then uncovered and rebagged without insect or any other organism visit. The foraging behaviour on A. mellifera capitula, its pollination efficiency, the fruiting rate, the percentage of mature achenes and the percentage of normal (well developed) achenes were evaluated. The results show that among 10 insect species recorded on C. sulphureus capitula after two seasons of observation, A. mellifera was the most represented with 95.57 % of 1128 visits. This bee harvested intensely nectar and pollen on C. sulphureus florets. The fruiting rate, the percentage of mature akenes and the percentage of normal achenes of treatments with unprotected capitula were significantly higher than those of treatments with capitula protected from insects. Through the pollination efficiency of a single capitule visit, A. mellifera increased the fruiting rate, the percentage of mature achenes and the percentage of normal achenes by 50.58 %, 14.37 % and 40.52 % respectively. The installation of A. mellifera colonies close to C. sulphureus fields is recommended to increase achenes and honey yields, as well as pollen production as a hive product.

Fertile Intersectional F1 Hybrids of 4x Vaccinium meridionale (Section Pyxothamnus) and Highbush Blueberry, V. corymbosum (Section Cyanococcus)

Vaccinium meridionale (section Pyxothamnus), a tetraploid species native to higher altitude locations in Jamaica, Colombia, and Venezuela, is of considerable interest to blueberry breeders for its profuse, concentrated flowering and monopodial plant structure, both of which may be useful in breeding for mechanical harvest. In this study, tetraploid V. meridionale was successfully hybridized as a male with 4x V. corymbosum (section Cyanococcus, highbush blueberry). The first-generation hybrids with highbush blueberry selections were intermediate in morphology and notably vigorous. The 4x F1 hybrids displayed variable branching structure, dormancy, prolificacy, fruit wax, etc.; however, most appear to be deciduous to semi-evergreen, with small, dark-colored fruit. The F1 hybrids displayed good fertility as females in backcrosses to 4x highbush and these crosses have produced numerous offspring morphologically indistinguishable from 4x highbush at the seedling stage. Evaluations of male fertility found variation for pollen production and quality but, significantly, found some clones with very good shed, high stainability, and almost complete tetrad production. The fertility suggests that these hybrids, despite being derived from intersectional crosses, might be conventionally used without significant difficulty. These hybrids also have potential value for the nascent V. meridionale breeding efforts occurring in Colombia, South America.

Geographic Patterns In Pollen Production In The Plant Ring Species Euphorbia tithymaloides In The Caribbean

Abstract—We examine investment in male function in the context of geography and floral morphology in the plant ring species Euphorbia tithymaloides, which colonized the Caribbean from Mexico/Guatemala along two fronts that roughly correspond to the Greater and the Lesser Antilles and that meet in the vicinity of the Anegada Passage. Our results on investment in pollen relative to ovule production are consistent with E. tithymaloides relying on pollinators for reproduction across its range in the Caribbean. We document a geographic pattern of reduction in anther number and pollen:ovule ratios in populations of E. tithymaloides towards the Anegada Passage, which is consistent with a possible geographic transition towards a mixed breeding system where selfing has increased importance in this area where its two expansion fronts meet. The reduction in pollen production is correlated with inflorescence morphology, which converges to relatively shorter cyathia towards the Anegada Passage along both fronts. We discuss alternative scenarios and potential drivers of the patterns we document.

Early Floral Resources for Urban Bees From Ornamental Shrubs Ribes Aureum, Ribes Sanguineum and Staphylea Pinnata

This research aims to assess ornamental shrubs Ribes aureum, R. sanguineum and Staphylea pinnata as an early food source for urban bees. In a two-year study, the abundance and flowering pattern, nectar and pollen production, and spectrum of urban insect visitors were investigated in Lublin, SE Poland. The apiarian value of S. pinnata was studied for the first time. The studied species exhibited abundant and extended flowering, skewed inflorescence flowering pattern, and persistent flowers and inflorescences. They bloomed from late March to late May and could be considered as valuable early foraging resources for urban bees, despite the substantial differences between the species. The highest mean sugar yield and pollen yield · plant−1 (92.9 g and 44.0 g, respectively) was estimated for S. pinnata whereas the lowest ones were found in R. sanguineum (4.3 g and 1.8 g, respectively). Hymenopterans were the principal flower visitors in the studied species accounting for more than 79% of all visits.

Pollen quality, pollen production and yield of some tomato (Solanum lycopersicum) genotypes under high temperature stress in Eastern Mediterranean

Pollen quality, pollen production and yield of different high temperature tolerant tomato genotypes were evaluated under Adana, Turkey conditions in two different periods. The control treatment (normal sown, where day/night temperatures during the vegetative and generative stage are below 32/20 °C) of the first period started on February 20, 2015. The seedlings in the second period were planted on May 15, 2015. The performances of twenty-four tomato genotypes (resistant and sensitive commercial genotypes) were compared to determine high temperature resistant and sensitive tomato genotypes. Significant relationship was obtained between the yield and the number of pollens. The results of the experiment revealed that ‘Tom173’, ‘Tom119’ and ‘F15656’ genotypes were more resistant, while ‘Tom108’ and ‘Tom10’ genotypes were more sensitive compared to the other tomato genotypes tested in the experiment.