Pollen Transmission Research Articles

Mutations in nuclear genes encoding mitochondrial ribosome proteins restore pollen fertility in S male-sterile maize.

The interaction of plant mitochondrial and nuclear genetic systems is exemplified by mitochondria-encoded cytoplasmic male sterility (CMS) under the control of nuclear restorer-of-fertility genes. The S type of CMS in maize is characterized by a pollen collapse phenotype and a unique paradigm for fertility restoration in which numerous nuclear restorer-of-fertility lethal mutations rescue pollen function but condition homozygous-lethal seed phenotypes. Two nonallelic restorer mutations recovered from Mutator transposon-active lines were investigated to determine the mechanisms of pollen fertility restoration and seed lethality. Mu Illumina sequencing of transposon-flanking regions identified insertion alleles of nuclear genes encoding mitochondrial ribosomal proteins RPL6 and RPL14 as candidate restorer-of-fertility lethal mutations. Both candidates were associated with lowered abundance of mitochondria-encoded proteins in developing maize pollen, and the rpl14 mutant candidate was confirmed by independent insertion alleles. While the restored pollen functioned despite reduced accumulation of mitochondrial respiratory proteins, normal-cytoplasm plants heterozygous for the mutant alleles showed a significant pollen transmission bias in favor of the nonmutant Rpl6 and Rpl14 alleles. CMS-S fertility restoration affords a unique forward genetic approach to investigate the mitochondrial requirements for, and contributions to, pollen and seed development.

Plant virus diversity in bee and pollen samples from apple (Malus domestica) and sweet cherry (Prunus avium) agroecosystems.

Honey bee (Apis mellifera) pollination is widely used in tree fruit production systems to improve fruit set and yield. Many plant viruses can be associated with pollen or transmitted through pollination, and can be detected through bee pollination activities. Honey bees visit multiple plants and flowers in one foraging trip, essentially sampling small amounts of pollen from a wide area. Here we report metagenomics-based area-wide monitoring of plant viruses in cherry (Prunus avium) and apple (Malus domestica) orchards in Creston Valley, British Columbia, Canada, through bee-mediated pollen sampling. Plant viruses were identified in total RNA extracted from bee and pollen samples, and compared with profiles from double stranded RNA extracted from leaf and flower tissues. CVA, PDV, PNRSV, and PVF coat protein nucleotide sequences were aligned and compared for phylogenetic analysis. A wide array of plant viruses were identified in both systems, with cherry virus A (CVA), prune dwarf virus (PDV), prunus necrotic ringspot virus (PNRSV), and prunus virus F (PVF) most commonly detected. Citrus concave gum associated virus and apple stem grooving virus were only identified in samples collected during apple bloom, demonstrating changing viral profiles from the same site over time. Different profiles of viruses were identified in bee and pollen samples compared to leaf and flower samples reflective of pollen transmission affinity of individual viruses. Phylogenetic and pairwise analysis of the coat protein regions of the four most commonly detected viruses showed unique patterns of nucleotide sequence diversity, which could have implications in their evolution and management approaches. Coat protein sequences of CVA and PVF were broadly diverse with multiple distinct phylogroups identified, while PNRSV and PDV were more conserved. The pollen virome in fruit production systems is incredibly diverse, with CVA, PDV, PNRSV, and PVF widely prevalent in this region. Bee-mediated monitoring in agricultural systems is a powerful approach to study viral diversity and can be used to guide more targeted management approaches.

Component-resolved diagnosis of tree pollen allergen: identify key allergens to develop treatment plans

With the increasing global prevalence of tree pollen allergies, there has been a significant impact on the quality of life for populations. In North and Central China, birch pollen, cypress pollen, and plane tree pollen are the most common allergens for springtime pollen allergy sufferers. The distribution of plants and patterns of pollen transmission in different geographical areas result in varying pollen exposure outcomes, further complicating the challenges in diagnosis and individualized treatment. This article delves into the research progress and clinical application of tree pollen allergies based on the "Molecular Allergology User's Guide 2.0 (MAUG 2.0) " published by the European Academy of Allergy and Clinical Immunology (EAACI). It discusses major allergen families and component proteins of tree pollen such as PR-10 proteins, profilins, polcalcins, as well as cross-reactive components that may cause pollen-food allergy syndrome. Allergen component diagnostics can distinguish true allergy sufferers from those with multiple allergen reactions, enabling more targeted selection of allergens for specific immunotherapy, thus enhancing treatment effectiveness. Bet v 1 and Cup a 1, for instance, are specific indicators for immunotherapy in birch and cypress allergy patients. Overall, this article provides cutting-edge information for professionals in the field of tree pollen allergies, offering in-depth exploration of tree pollen allergen component proteins, clinical manifestations, and treatment-related research, aiding in better understanding and addressing the challenges of tree pollen allergies.

Seed and pollen transmission of tomato leaf curl New Delhi virus, tomato leaf curl Taiwan virus, and tomato yellow leaf curl Thailand virus in cucumbers and tomatoes.

Understanding the seed-borne nature of plant viruses is essential for developing disease control strategies and is impactful to the seed market. Here, we investigated seed transmissibility of tomato leaf curl New Delhi virus-cucumber isolate (ToLCNDV-CB) and -oriental melon isolate (ToLCNDV-OM) in cucumber and seed transmissibility of tomato leaf curl Taiwan virus (ToLCTV) and tomato yellow leaf curl Thailand virus (TYLCTHV) in tomato. Parent plants were inoculated using agroinfiltration with virus infectious clones, and virus infection was confirmed by PCR with virus-specific primers. ToLCNDV-CB and ToLCNDV-OM were detected in different parts of the female and male flowers and the fruits of cucumbers. ToLCNDV-CB and ToLCNDV-OM were also detected in cucumber seed coats and seedlings with an infection rate higher than 79%. Similar results were observed with ToLCTV and TYLCTHV as they were detected in different parts of the female and male flowers and fruits of three tomato cultivars. ToLCTV and TYLCTHV were also detected in tomato seed coats and seedlings with an infection rate higher than 36%. In addition, pollen-mediated transmission assays of these four begomoviruses were conducted with pollen derived from virus-infected plants to healthy plants. Results showed that ToLCNDV-CB and ToLCNDV-OM were detected in cross-pollinated cucumber progenies with an infection rate higher than 70%. ToLCTV and TYLCTHV were [also] detected in cross-pollinated tomato progenies with an infection rate higher than 77%. Our results indicated that ToLCNDV, ToLCTV, and TYLCTHV can be transmitted via seeds or pollens of cucumber and tomato plants. To our knowledge, this is the first report documenting the pollen-mediated transmission of begomoviruses.

Disruption of pollen tube homogalacturonan synthesis relieves pollen tube penetration defects in the Arabidopsis O-FUCOSYLTRANSFERASE1 mutant.

During angiosperm sexual reproduction, pollen tubes must penetrate through multiple cell types in the pistil to mediate successful fertilization. Although this process is highly choreographed and requires complex chemical and mechanical signaling to guide the pollen tube to its destination, aspects of our understanding of pollen tube penetration through the pistil are incomplete. Our previous work demonstrated that disruption of the Arabidopsis thaliana O-FUCOSYLTRANSFERASE1 (OFT1) gene resulted in decreased pollen tube penetration through the stigma-style interface. Here, we demonstrate that second site mutations of Arabidopsis GALACTURONOSYLTRANSFERASE 14 (GAUT14) effectively suppress the phenotype of oft1 mutants, partially restoring silique length, seed set, pollen transmission, and pollen tube penetration deficiencies in navigating the female reproductive tract. These results suggest that disruption of pectic homogalacturonan (HG) synthesis can alleviate the penetrative defects associated with the oft1 mutant and may implicate pectic HG deposition in the process of pollen tube penetration through the stigma-style interface in Arabidopsis. These results also support a model in which OFT1 function directly or indirectly modifies structural features associated with the cell wall, with the loss of oft1 leading to an imbalance in the wall composition that can be compensated for by a reduction in pectic HG deposition.

Infectivity of highly pathogenic isolates of potato spindle tuber viroid in dahlia

Dahlias that are naturally infected with potato spindle tuber viroid (PSTVd) do not exhibit symptoms. Therefore, if PSTVd isolates that are highly pathogenic in tomato plants infect dahlias, there is a significant risk of PSTVd infecting other plants via dahlias. In this study, we found that almost all highly pathogenic isolates were able to infect dahlia plants, but the symptoms varied depending on the cultivar. When mixed inocula composed of dahlia isolates and highly pathogenic isolates were tested, the dahlia isolates dominantly infected dahlia plants; however, the highly pathogenic isolates also coinfected plants. Our results also suggest that seed or pollen transmission from infected dahlia plants does not occur.

Overexpressing Vitamin C Defective 2 reduces fertility and alters Ca2+ signals in Arabidopsis pollen.

A potential strategy to mitigate oxidative damage in plants is to increase the abundance of antioxidants, such as ascorbate (i.e. vitamin C). In Arabidopsis (A. thaliana), a rate-limiting step in ascorbate biosynthesis is a phosphorylase encoded by Vitamin C Defective 2 (VTC2). To specifically overexpress VTC2 (VTC2 OE) in pollen, the coding region was expressed using a promoter from a gene with ∼150-fold higher expression in pollen, leading to pollen grains with an eight-fold increased VTC2 mRNA. VTC2 OE resulted in a near-sterile phenotype with a 50-fold decrease in pollen transmission efficiency and a five-fold reduction in the number of seeds per silique. In vitro assays revealed pollen grains were more prone to bursting (greater than two-fold) or produced shorter, morphologically abnormal pollen tubes. The inclusion of a genetically encoded Ca2+ reporter, mCherry-GCaMP6fast (CGf), revealed pollen tubes with altered tip-focused Ca2+ dynamics and increased bursting frequency during periods of oscillatory and arrested growth. Despite these phenotypes, VTC2 OE pollen failed to show expected increases in ascorbate or reductions in reactive oxygen species, as measured using a redox-sensitive dye or a roGFP2. However, mRNA expression analyses revealed greater than two-fold reductions in mRNA encoding two enzymes critical to biosynthetic pathways related to cell walls or glyco-modifications of lipids and proteins: GDP-d-mannose pyrophosphorylase (GMP) and GDP-d-mannose 3',5' epimerase (GME). These results support a model in which the near-sterile defects resulting from VTC2 OE in pollen are associated with feedback mechanisms that can alter one or more signaling or metabolic pathways critical to pollen tube growth and fertility.

Advances in plastid transformation for metabolic engineering in higher plants.

The plastid (chloroplast) genome of higher plants is an appealing target for metabolic engineering via genetic transformation. Although the bacterial-type plastid genome is small compared with the nuclear genome, it can accommodate large quantities of foreign genes that precisely integrate through homologous recombination. Engineering complex metabolic pathways in plants often requires simultaneous and concerted expression of multiple transgenes, the possibility of stacking several transgenes in synthetic operons makes the transplastomic approach amazing. The potential for extraordinarily high-level transgene expression, absence of epigenetic gene silencing and transgene containment due to the exclusion of plastids from pollen transmission in most angiosperm species further add to the attractiveness of plastid transformation technology. This minireview describes recent advances in expanding the toolboxes for plastid genome engineering, and highlights selected high-value metabolites produced using transplastomic plants, including artemisinin, astaxanthin and paclitaxel.

Proline-rich extensin-like receptor kinases PERK5 and PERK12 are involved in pollen tube growth.

Proline-rich extensin-like receptor kinases (PERKs) belong to the hydroxyproline-rich glycoprotein (HRGP) superfamily known to be involved in many plant developmental processes. Here, we characterized two pollen-expressed PERKs from Arabidopsisthaliana, PERK5 and PERK12. Pollen tube growth was impaired in single and double perk5-1 perk12-1 loss of function mutants, with an impact on seed production. When the segregation was analysed, a male gametophytic defect was found, indicating that perk5-1 and perk12-1 mutants carry deficient pollen transmission. Furthermore, perk5-1 perk12-1 displayed an excessive accumulation of pectins and cellulose at the cell wall of the pollen tubes. Our results indicate that PERK5 and PERK12 are necessary for proper pollen tube growth, highlighting their role in cell wall assembly and reactive oxygen species homeostasis.

On pollen and airborne virus transmission.

This study investigates how airborne pollen pellets (or grains) can cause severe respiratory-related problems in humans. Given that pollen pellets can capture ribonucleic acid viruses, we show that airborne pollen grains could transport airborne virus particles such as the airborne coronavirus (CoV) disease (COVID-19) or others. We consider the environmental conditions featuring the highest pollen concentration season and conduct computational multiphysics, multiscale modeling and simulations. The investigation concerns a prototype problem comprising the transport of 104 airborne pollen grains dropped from a mature willow tree at a wind speed of . We show how pollen grains can increase the coronavirus (CoV) transmission rate in a group of people, including some infected persons. In the case of high pollen grains concentrations in the air or during pollination in the spring, the social distance of 2 m does not hold as a health safety measure for an outdoor crowd. Thus, the public authorities should revise the social distancing guidelines.

Visualization of the seasonal shift of a variety of airborne pollens in western Tokyo

Airborne pollens cause pollinosis and have the potential to affect microphysics in clouds; however, the number of monitored species has been very limited due to technical difficulties for the morphotype identification. In this study, we applied an eDNA approach to the airborne pollen communities in the suburbs of the Tokyo metropolitan area in Japan, within a mixed urban, rural, and mountain landscape, revealing pollen seasonality of various taxa (a total of 78 families across the period) in the spring season (February to May). Those taxa distinctly shifted in the season, especially in the beginning of February and the middle of April. Air temperature shift was an obvious key factor to affect the airborne pollen community, while the influence of other meteorological factors, such as wind speed, humidity, and precipitation, was not clear. Taxonomic classification of major Amplicon Sequence Variants (ASVs) indicates multiple pollen sources, including natural forest, planted forest, roadside, park lands, and horticultural activities. Most major ASV belongs to Japanese cedar (Cryptomeria japonica), which is the most notable allergen that causes pollinosis in Japan, peaking in mid-February to March. Backward trajectory analysis of air masses suggests that the Japanese cedar and other Cupressaceae plantation forests in the western mountains were a significant source of airborne pollen communities detected at our sampling site. Other major plant pollen sources, including Japanese zelkova (Zelkova serrata) and ginkgo (Ginkgo biloba), emanated from the nearby parks or roadside regions. This study's approach enables us to visualize the phenology of multiple pollen, including timing and duration. Long-term monitoring of this type would provide additional insight into understanding the role of climate change on pollen transmission and links to flowering events.

Hemp Production Network Effects: Are Producers Tipped Toward Suboptimal Varietal Selection by Their Neighbors?

The 2018 farm bill removed industrial hemp from the Schedule 1 Controlled Substance List. In response, states scrambled to enact hemp legislation. Some hemp flower producers report their hemp fields were cross- pollinated by a neighbor growing a different hemp cultivar. For hemp flower crops, cross- pollination reduces cannabinoid concentration levels within the flower; these concentration levels dictate flower price. We show that in a repeated game, once a sufficiently large percentage of growers decide to plant hemp fiber/seed crops, cross-pollination forces flower growers to convert to fiber/seed to avoid the negative network externality. Over time, a stable, suboptimal Nash equilibrium of reduced flower production results. The most important factor driving this tip to reduced flower production is pollen transmission rates between fields. This factor can be effectively reduced through either an auction-style quota system directed at seed and fiber cultivars or intertemporal zoning laws that dictate when a particular cultivar can be planted. As applications for hemp growing licenses swell, cross- pollination between farmers becomes increasingly likely. If left unchecked by policy, farm-level income and rural economic development will be suppressed.

Arabidopsis Ca2+-ATPases 1, 2, and 7 in the endoplasmic reticulum contribute to growth and pollen fitness.

Generating cellular Ca2+ signals requires coordinated transport activities from both Ca2+ influx and efflux pathways. In Arabidopsis (Arabidopsis thaliana), multiple efflux pathways exist, some of which involve Ca2+-pumps belonging to the Autoinhibited Ca2+-ATPase (ACA) family. Here, we show that ACA1, 2, and 7 localize to the endoplasmic reticulum (ER) and are important for plant growth and pollen fertility. While phenotypes for plants harboring single-gene knockouts (KOs) were weak or undetected, a triple KO of aca1/2/7 displayed a 2.6-fold decrease in pollen transmission efficiency, whereas inheritance through female gametes was normal. The triple KO also resulted in smaller rosettes showing a high frequency of lesions. Both vegetative and reproductive phenotypes were rescued by transgenes encoding either ACA1, 2, or 7, suggesting that all three isoforms are biochemically redundant. Lesions were suppressed by expression of a transgene encoding NahG, an enzyme that degrades salicylic acid (SA). Triple KO mutants showed elevated mRNA expression for two SA-inducible marker genes, Pathogenesis-related1 (PR1) and PR2. The aca1/2/7 lesion phenotype was similar but less severe than SA-dependent lesions associated with a double KO of vacuolar pumps aca4 and 11. Imaging of Ca2+ dynamics triggered by blue light or the pathogen elicitor flg22 revealed that aca1/2/7 mutants display Ca2+ transients with increased magnitudes and durations. Together, these results indicate that ER-localized ACAs play important roles in regulating Ca2+ signals, and that the loss of these pumps results in male fertility and vegetative growth deficiencies.

How will climate change alter the dynamics of airborne pollen and pollen load of allergenic plants?

Summary Background Globally, climate change is being observed. Pollen allergies have been increasing since the middle of the last century. Outdoors, sensitization against pollen allergens is responsible for the highest prevalence of allergies of eyes and airways. Hence, the following two questions arose: (1) How does climate change become manifest locally–regionally, and do temperatures and precipitation have to be considered exceptional in 2018? (2) How do changing meteorological conditions impact on pollination and pollen load? Methods Pollen data of the main allergenic plants—collected at the pollen monitoring station Linz, Upper Austria—were analysed; 2018 was compared to the years 1993–2017. By means of statistical methods, the impact of meteorological parameters on pollen seasons and pollen load were examined. Results Climate change was confirmed for the region. The regional climate has shifted from moderate to warmer and drier (semi-arid) conditions. Preseasonal cumulated meteorological parameters determined flowering and pollen seasons (PS). Start and duration of the pollination of hazel, alder, birch, and grass followed other rules than the seasonal pollen production, termed seasonal pollen integral (SPIn). By its hybrid character, the model-year 2018 offered the unique chance to generate and explain different scenarios of pollen emission and transmission. For the start of flowering of hazel (Corylus), alder (Alnus) and birch (Betula), the coincidence of cumulated mean daily warmth (MDWcumul) and a distinct threshold for the highest temperature of a day (HTD) is necessary and species-specific. In 2018, the earliest begin of the pollen season (PSB) was observed. Frost delayed the PSB. Preseasonal frost as well as cool temperatures caused SPIn of alder and birch to rise, whereas SPIn of hazel were increased by warmer temperatures. Warm weather prolonged pollen seasons of early flowering plants. Heat combined with drought shortened PS of birch in 2018. Cumulated relative humidity (RHcumul) correlated highly significant with the PSB of grasses. Warm and dry conditions in 2018 caused the earliest PSB of grass since 1993. Over the years, SPI and major pollen peaks of grasses have decreased, primarily due to dryness. Conclusion The assumption that climate warming in Linz over 26 years should have increased pollen concentrations of allergenic plants was not confirmed. On the contrary, trend analyses showed that the pollen load has decreased. Hence, the increase in sensitization to pollen allergens and of the prevalence of pollen allergies ask for other explanations.

The Potential of Mangrove-Derived Organic Matter in Sediments for Tracing Mangrove Development During the Holocene

The responses of mangroves to future climate change can be reconstructed from past mangrove dynamics using proxies preserved in sediments. The contributions of mangrove-derived organic matter (MOM) can be calculated by using δ13Corg and molar C:N values. In order to verify the effectiveness of MOM for tracing mangrove development, four typical regions are chosen, including the Beibu Gulf of SW China, western coast of peninsular India, Flamenco Lagoon of Puerto Rico, and Amazon estuary of northern Brazil. The results showed that the temporal variation of calculated MOM is similar to the abundance of mangrove pollen (MP) in each core. There are significant positive correlations between them, with correlation coefficients ranging from 0.68 to 0.89 (P 0.05, n = 281) between MOM and MP globally, owing to the complexities of OM provenance and pollen transmission. It is indicated that MOM is a potential proxy for regional mangrove development during the Holocene. The proxy should be useful to reconstruct high-resolution mangrove development, owing to its easily fine-cut sampling and cheaper cost of instrumentation compared with pollen and biomarkers.

Identification of a WD-repeat protein that binds and activates the deubiquitinase UBP3 from Arabidopsis thaliana

Ubiquitination is a post-translational modification of proteins that plays an essential role in many cellular processes. Ubiquitination involves the attachment of the small polypeptide ubiquitin to target proteins to control their activity or stability. As a reversible modification, E3 ubiquitin-ligases attach ubiquitin to proteins while deubiquitinases (DUBs) remove ubiquitin from tagged proteins. Revealing the mechanisms that regulate ubiquitination/deubiquitination is important for understanding how cells fine-tune protein activity to control important processes and pathways. It is clear in animals and yeast that WD-repeat proteins (WDR) bind to and activate DUBs. In plants, however, no interactions between WDR proteins and DUBs have been reported. Here, we used BLAST searches to identify plant homolog proteins of a conserved animal DUB and its associated WDR proteins. Based on these homologies, we predicted that Arabidopsis UBP3, a DUB involved in pollen development and transmission, forms a complex with the WDR proteins At2g37160 and LRS1. Indeed, these three proteins could be co-immunoprecipitated when transiently co-expressed as epitope-tagged proteins in plant cells. At2g37160 also interacted with UBP3 in the yeast two-hybrid system and could enhance the DUB activity of UBP3 ten-fold in vitro. These results provide the first evidence that plant DUBs, like animal DUBs, are regulated by WDR proteins.

A new isolation device for shortening gene flow distance in small-scale transgenic maize breeding

The transmission of pollen is the main cause of maize gene flow. Under the compulsory labeling system for genetically modified (GM) products in China, isolation measures are crucial. At present, there is no effective isolation device for preventing and controlling the short-range flow of GM maize pollen. The purposes of the present experiments were to overcome the deficiencies of existing technology and to demonstrate a new isolation device for decreasing the gene flow distance of GM maize. The isolation device we invented was shown to be more robust than traditional isolation methods, and it can be disassembled and repeatedly reused. The most important point was that the frequency of gene flow could be greatly reduced using this device. When the distance from the isolation device was more than 1 m, the gene flow rate could be decreased to less than 1%, and when the distance from the isolation device was more than 10 m, the gene flow rate could be reduced to less than 0.1%. When the isolation device was adopted to isolate GM maize in conjunction with bagging the tassels of GM maize at the pollination stage, the gene flow could be controlled to less than 0.1% when the distance from the isolation device was more than 1 m. This device was, however, only applicable for small plots and can shorten the isolation distance of GM maize planting and improve the purity of seeds, all while meeting the needs of close isolation breeding. The use of this device represents a feasible method for risk prevention and control of GM crops.

English

Three pollination control tents (PCTs) made from novel nonwoven synthetic fabrics with more open pore structure (DWB10, DWB23 and DWB24) were compared with the standard DWB01 fabric for pollen proofing in sugar beet (Beta vulgaris L.) at the research station of Lion Seed Ltd Essex, UK in 2019. PCTs of 63.5 x 63.5 cm footprint accommodated single potted plants. A completely randomised trial with five replications including an open pollinated control was conducted using cytoplasmic male sterile line 1TM37. Analysis was computed for (a) full data and (b) excluding three DWB23 defective tents. Differences among treatments were non-significant for all morphological traits except for number of secondary branches in (a) only. There was thus no micro-climatic difference among treatments for morphological traits of the 1TM37 CMS line. Among the seed related traits, 1000-seed weight and 10-day germination (%) were significant between treatments in (a) but only 1000-seed weight in (b). The mean 1000-seed weight was significantly higher for the open control than all other PCT treatment means which did not differ significantly from zero. Therefore, all four fabrics of PCTs were equally pollen proof in preventing pollen contamination. It is concluded for the first time that mini-tents of these novel nonwoven fabrics, engineered for both larger pores for air permeability and fibre architecture to prevent pollen transmission, adequately eliminated cross-pollination while maintaining ambient environmental conditions and are effective for sugar beet breeding. The PCT technology may be equally usefully deployed in other traditional, commercial and fibre crops for hybrid seed production. Key words: Sugar beet, nonwoven synthetic fabric, pollination control tent, male sterility. &nbsp

The raspberry bushy dwarf virus 1b gene enables pollen grains to function efficiently in horizontal pollen transmission

Horizontal pollen transmission by the raspberry bushy dwarf virus 1b deletion mutant (RBΔ1bstop), which is defective in virus virulence, was significantly decreased compared to wild-type raspberry bushy dwarf virus (wtRBDV). We assessed accumulation of viral genomic (g) RNAs in pollen grains from RBΔ1bstop-infected plants and found that the pollen grains had less viral gRNA than those from wtRBDV-infected plants. In addition, pollen grains from 1b-expressing transgenic plants (1b-plants) infected with RBΔ1bstop were more efficient in horizontal virus transmission to healthy plants after pollination than pollen from RBΔ1bstop-infected wild type plants. Moreover, viral gRNA accumulation in pollen grains from RBΔ1bstop-infected 1b-plants was higher than in pollen from RBΔ1bstop-infected wild type plants. We suggest that 1b increases the amount of viral gRNAs released from elongating pollen grains.

Large-scale pollen distribution in marine surface sediments from the Bohai Sea, China: Insights into pollen provenance, transport, deposition, and coastal-shelf paleoenvironment

To elucidate the mechanisms responsible for pollen and spore transportation and deposition in the Bohai Sea, fully covered seafloor-surface sediment samples were collected for palynological and grain size analysis. The results reveal that the pollen and spore concentrations were higher in the head of Liaodong Bay and in the muddy area of the Bohai Sea. The Yellow River was the main source of pollen and spores in the Bohai Sea. The sediments with relatively high pollen concentrations consisted mainly of clay and fine silt, whereas sediment with lower pollen concentrations was mostly fine sand. In addition, the percentages of Pinus pollen and pteridophyte spores increased with increasing sea water depth, while other arboreal (excluding Pinus) and herbaceous pollen generally decreased with increasing distance from the shore. The relationship between the pollen taxa and the water depth of the sampling points shows that the fluvial water plays a predominant role in pollen transmission within 20 m of water depth, while the wind is the main driving force for pollen transmission when the water depth exceeds 20 m. Although Pinus pollen and pteridophyte spores were over-represented, there was good correlation between marine pollen signals and terrestrial vegetation. Apart from the influence of rivers and wind on pollen and spore deposition, the tidal currents and circulation were also main force responsible for transporting sediment and determining the differentiation of pollen and spores in the Bohai Sea. The comparison of pollen and spore percentages between surface sediment and fossil records from sedimentary cores made it possible to identify changes in pollen sources and transport mechanisms. Meanwhile, the percentage fluctuations of fossil Pinus and herbaceous pollen revealed concomitant changes of the sea level and climate. These findings are of paramount importance to the interpretation of Quaternary marine pollen data from the Bohai Sea, China.