Revisiting the role of pollen-microbiome interactions: new insights into the 'One Health -One Biosecurity' concept in changing agroecosystems

Jakab Máté SchermanGábor Markó^*Erzsebet SzathmaryGéza NagyIvett KocsisMarietta Petróczy

• Hungarian University of Agriculture and Life Sciences, Budapest, Hungary

The One Health-One Biosecurity framework recognizes the interconnectedness of human, animal, plant, and environmental health (Hulme, 2020). This concept can easily be illustrated through plant diseases caused by phytopathogens. For example, the cereal crop pathogen Fusarium graminearum principally infects hosts through floral tissues (Khalaf et al., 2021), resulting in significant yield losses and contamination of grains with mycotoxins like deoxynivalenol. This toxin not only threatens plant health and agricultural productivity but also poses serious feed and food safety risks for humans and animals, causing gastrointestinal symptoms, feed refusal, and broader public health concerns (Patriarca and Fernández Pinto, 2017). The pathogenesis is influenced by several major factors shaped by many contributing subfactors that may be relevant in the context of increasing pathogen pressure in agroecosystems. One such element is the presence of pollen grains, whose specific role is underrepresented.Pollen is widely recognized as essential for plant sexual reproduction, promoting genetic and phenotypic diversity among offspring (Hafidh and Honys, 2021). However, its ecological role extends far beyond pollination. Increasing evidence suggests that pollen grains serve as primary and supplementary nutrient sources, influencing not only plant-pollinator relationships but also plant-microbe interactions. For instance, pollen consumption improves pollinator reproduction (Eeraerts et al., 2021), while pollen extracts support the growth of several pathogenic and non-pathogenic fungi (Huang et al., 1998). Water-soluble pollen exudates may increase the virulence of plant pathogens (Fourie and Holz, 1998), and the presence of pollen grains supports early fungal development and the initial stages of pathogenesis (Chou and Preece, 1968;Allen et al., 1983). These findings suggest a potentially underestimated role of pollen in shaping plant disease dynamics, particularly relevant in the context of increasing pathogen pressure in agroecosystems.Plant surfaces (e.g., leaves, bark) naturally accumulate airborne particles as passive traps, capturing pollen grains (Faegri et al., 1989;Groenman-van Waateringe, 1998;Zhang et al., 2020) and fungal spores (Magyar, 2008).Increasing evidence suggests that pollen grains and their water-soluble exudates serve as primary and supplementary nutrient sources for microbes. These humid, nutrient-rich microhabitats promote spore germination, growth, and infection of several pathogenic and non-pathogenic fungi (Hennebert, 1973;Huang et al., 1998). ). The presence of pollen increases the virulence of plant pathogens (Fourie and Holz, 1998), which is crucial in the early stages of fungal development and pathogenesis (Chou and Preece, 1968;Allen et al., 1983).Early experiments highlightedrevealed a pollen-driven stimulatory effect on certain host plant-pathogen interactions (Bachelder and Orton, 1962;Chou and Preece, 1968). Recent research has shown that this phenomenon may extend beyond host specificity, indicating a broader ecological mechanism (Kocsis et al., 2022). YetNevertheless, the mechanisms behindunderlying pollen-stimulated spore germination, speciesspecific variationvariations, and microbiome-driven effects remain poorly understood.The phyllosphere-the microbial habitat on leaf surfaces-is shaped by external inputs, such as airborne pollen, spores, and pollutants (Annamalai and Namasivayam, 2015). Notably, pollen grains are not sterile; they harbor diverse microbial communities, including bacteria (Manirajan et al., 2018), fungi (Naggar and Sallam, 2009), and viruses (Fetters and Ashman, 2023). These microorganisms along with airborne pollen, spores, and other pollutants may influence the structure and function of phyllosphere microbiota (Annamalai and Namasivayam, 2015;Leveau, 2019). AIn human-altered ecosystems, such as agricultural fields, a diverse microbiome is associated with has been shown to improve plant health and enhanced, thereby enhancing disease resistance, particularly in human-disturbed ecosystems such as agricultural fields (Berg and Koskella, 2018;Perreault and Laforest-Lapointe, 2022).The relevance of these interactions is underscored by the One Health-One Biosecurity framework, which recognizes the interconnectedness of human, animal, plant, and environmental health (Hulme, 2020). Plant pathogens, such as Fusarium graminearum, infect cereal crops through floral tissues (Khalaf et al., 2021), leading to significant yield losses and the contamination of grains with the mycotoxin deoxynivalenol.Therefore, this opinion article aims to review the current evidence on the role of pollenassociated microbiota in plant-pathogen interactions, explore its relevance within the One Health-One Biosecurity framework, and identify critical research gaps while suggesting future research targets This toxin not only threatens plant health and agricultural productivity but also poses serious feed and food safety risks for humans and animals, causing gastrointestinal symptoms, feed refusal, and broader public health concerns (Patriarca and Fernández Pinto, 2017). Although researchers know little about how pollen and the associated microbiomes influence the initial development of plant pathogens, and how the phyllosphere can influence this.Therefore, we aimed to highlight the modifying role of pollen in pathogen-microbiome interactions within the context of the One Health-One Biosecurity framework. By summarizing current knowledge and identifying critical gaps, we seek to stimulate future research that is essential for advancing agricultural production and crop protection. Pollen disperses via wind or pollinators over varying distances (Wessinger, 2021;Rodrigues et al., 2023).Most airborne pollen originates from anemophilous plants, and the dispersal patterns vary according to flowering periods (Jones and Harrison, 2004;Wozniak and Steiner, 2017).), atmospheric conditions (Raynor et al., 1974), unique pollen morphology (e.g., Ambrosia: spiked structure; Pinus: air-filled bladders), and water content (Schwendemann et al., 2007;Sabban and van Hout, 2011). Wind-pollinated crops such as corn (Zea mays) and sugarcane (Saccharum officinarum) dominate global grain and sugar production (Klein et al., 2007), and common wind-pollinated weed species, including Artemisia and Rumex genera, or the Poaceae and Urticaceae families, contribute significantly to airborne pollen loads (Bogawski et al., 2014).Fungal aerosols also arise from vegetation, with plant leaf surfaces serving as key sources of airborne propagules (Awad, 2005;Qi et al., 2020). Agricultural systems harbor crop-specific pathogenic fungi that produce large quantities of spores (Obayori, 2023). The most prevalent airborne fungal genera from agriculture include Alternaria, Cladosporium, Penicillium, Aspergillus, and Fusarium (Al-Shaarani and Pecoraro, 2024). FungalThe vast majority of plant pathogens are airborne (Fagade et al., 2023), and their spore production and dispersal are influenced by weather, geography, and human activities (Cho et al., 2006). Thus, natural habitats and agricultural landscapes are primary and major sources of airborne pollen and spores.Beyond wind-mediated dispersal, insect pollinators play a centralsignificant role in pollen transport and plant fertilization. Hymenoptera and Lepidoptera species are the primary vectors (Primack and Silander, 1975;Schemske and Horvitz, 1984;Herrera, 1987). Over one-third of agricultural crops depend on insect pollination (Klein et al., 2007), withincluding key crops such as oil-palm (Elaeis guineensis), soybean (Glycine max), sunflower (Helianthus annuus), and rapeseed (Brassica napus) being key insect-pollinated crops that significantly contribute to global food systems (Roubik, 2018). Pollination type influences the diversity and composition of pollen-associated microbiota (Ambika Manirajan et al., 2016) and facilitates fungal spore contamination.which are essential contributors to global food systems (Roubik, 2018).The vast majority of plant pathogens are airborne (Fagade et al., 2023) and, together with pollen grains, play a role in cloud formation as cloud condensation nuclei (Ariya and Amyot, 2004). Pollen grains can absorb up to 100% of their weight in water under humid conditions (Diehl et al., 2001). Airborne dispersal depends on atmospheric conditions and can occur over considerable distances from the source (Raynor et al., 1974).Unique pollen morphology (e.g., Ambrosia: spiked structure; Pinus: air-filled bladders) and water content affect settling velocities in the air (Schwendemann et al., 2007;Sabban and van Hout, 2011). The watersoluble fraction of cloud vapor from broken pollen grains consists of sugars (e.g., fructose, glucose, sucrose, trehalose) and sugar alcohols (e.g., arabitol, inositol, mannitol), creating a nutrient-rich microenvironment for spore germination (Wang et al., 2007;Yttri et al., 2007;Hayer et al., 2013). Pollen grains travelling in the air with fungal spores, and their masses taking up water and chemicals during cloud formation, can be favorable for these biological interactions, enhancing pathogen viability during airborne dispersal.Pollinators interact with numerous flowers during feeding, acting as microbial vectors and mixing pollen (Brett, 1966) and related microbiota across plant species. ThisThe activity of pollinator species, and the floral abundance can directly or indirectly shape microbial communities (Wei et al., 2021). For example, honeybee behavior increases bacterial diversity, introducing honeybee symbionts, bee pathogens, and nectar-associated microbes (Prado et al., 2022). Pollinator type, activity, and floral abundance can directly or indirectly shape microbial communities (Wei et al., 2021). Interestingly, insect-pollinated species may host microbiomes more similar to wind-pollinated species, potentially due to this microbial exchange (Ambika Manirajan et al., 2016).Honeybees also spread the flower pathogen Erwinia amylovora while foraging (Cellini et al., 2019). Other pseudo-flower and flower-scent-producing pathogens, such as Puccinia spp., Microbotryum violaceum, or Monilinia vaccinii-corymbosi, are also pollinator-dispersed (Raguso and Roy, 1998;Dötterl et al., 2009;McArt et al., 2016). Similarly, honeybees can incidentallyalso disseminate fungal spores incidentally collected from insect honeydew or from plant surfaces (Shaw, 2015). Honeydew supports the germination of mold fungi such as Alternaria and Cladosporium, affecting airborne allergen levels (Magyar et al., 2022). Besides transport, pollinators mix pollen grains and fungal spores across plants (Brett, 1966). During pollen transport, spores can penetrate and colonize pollen, which is advantageous for pathogenesis (Magyar et al., 2022). Pollen grains and fungal spores are common allergens, and co-exposure can intensify symptoms (Codina et al., 2021;Myszkowska et al., 2023).Interactions between pollen and microbes can occur at different levels, such as in the atmosphere and in the phyllosphere. Pollen grains can absorb up to 100% of their weight in water under humid conditions (Diehl et al., 2001). Due to their large size and hygroscopic properties, pollen grains, together with airborne spores, play a role in cloud formation as cloud condensation nuclei (Ariya and Amyot, 2004). The extraction of pollen grains and mobilization of nutrients could start in this aqueous environment. The water-soluble fraction of cloud vapor from pollen grains contains sugars (e.g. fructose, glucose, sucrose, trehalose) and sugar alcohols (e.g. arabitol, inositol, mannitol), which, when falling with the precipitation, create a nutrient-rich and stimulating microenvironment for spore germination (Wang et al., 2007;Yttri et al., 2007;Hayer et al., 2013).AfterAt the phyllosphere level, the accumulation of pollen grains and fungal spores on plant surfaces, these environments provideprovides nutrients and chemical trigger molecules that facilitate microbial developmentfor fungal spores. The rapid biological exploitation of pollen resources by both parasitic and saprophytic microorganisms has been well-documented.is evidence based. For example, pollen grains of corn have been shown to stimulate the early germination of macroconidia spores in Fusarium species, which cause serious stem rot (Naik and Busch, 1978). The presence of pollen stimulates spore germination of Botrytis cinerea as well (Chou and Preece, 1968;Kocsis et al., 2022). For litter-and wood-decaying fungi, including members of the Basidiomycota (Hutchison and Barron, 1997) and Phycomycetes (Goldstein, 1960), pollen provides a supplementary seasonal source of nutrients. This phenomenon is a general stimulatory effect, as the initial development of many fungal species can be widely triggered by pollen extracts. Furthermore, it has been demonstrated that this effect is not plant species specific, because pollen grains of numerous plant species exert an influence on the same fungal species (Kocsis et al., 2022).Droplet transmissionDroplets containing pollen can also harbor bacteria that affect fungal spore germination.Bacteria are often observed surrounding fungal spores, such as Botrytis cinerea, on leaf surfaces, where they inhibit spore germination by depleting available nutrients (Blakeman, 1973). Recent research has uncovered that maize pollen harbors beneficial bacteria capable of suppressing fungal pathogens, highlighting pollen's role beyond fertilization (Shrestha et al., 2024). This discovery emphasizes the importance of considering pollen as a dynamic microenvironment influencing plant-microbe interactions and pathogen dynamics.Studies have shown that the presence of pollen increases the performance of beneficial microorganisms used in biological control strategies (Li et al., 2003). Thus, although pollen generally stimulates pathogen spore germination by enriching the microenvironment, it can also enhance the effectiveness of biological control agents. In the last two decades, the microbiome concept has revolutionized our understanding of organismenvironment interactions, particularly through the lens of ecological network theory (Foster et al., 2008).Recently, attention has turned toward the interactions between pollen and its associated microbiome, opening up new perspectives in plant ecology, health, and crop production. The composition of the pollen microbiome is taxon-specific (Armstrong et al., 2024); however, human-related environmental factors, such as agricultural activities, pollution, and urbanization, also modify these communities (Obersteiner et al., 2016).The impact of pollen-associated microbiomes on reproductive success (i.e., crop yield and quality) and longterm fitness consequences is crucial for plants living in natural or agricultural environments (Zasloff, 2017).Future research should prioritize understanding how microbial colonization interferes with pollen--pistil compatibility and signaling pathways, including signaling proteins and the sensitivity of recognition receptors, and how these factors affect fertilization efficiency, post-pollination processes (i.e., pollen tube growth or stigma health), seed set, and fruit development. Moreover, pollen microbiomes may be transmitted to seeds (Wu et al., 2022;Cardinale and Schnell, 2024), raising important questions about the inheritance of beneficial microbiomes and their role in plant fitness. Changes in pollen microbiome composition, which are associated with phylogenetic variation, contribute to host diversification (Khalaf et al., 2023).Similarly, The pollen microbiome composition is taxon-specific (Armstrong et al., 2024). Therefore, a thorough examination of the role of pollinatorspollination type, pollinator, and wind-mediated transfer in dispersing both beneficial and pathogenic microbes should be examined more deeplyis imperative.Understanding animal behavioral aspects (i.e., flower preference and feeding), as well as the implications for animal health and honey production, is crucial. In a broader context, pollinatorsthe transfer of pollen may facilitateinfluence evolutionary processes through horizontal gene transfer, enabling gene flow between microbial communities across ecosystems. Pollen grains and fungal spores, notably those of the Alternaria species, have been observed to be transferred together (Magyar et al., 2022). This co-transfer provides an opportunity for gene transfer between different Alternaria alternata strains, a phenomenon that has already been documented (Mehrabi et al., 2011). These processes are especially important in agroecosystems, where pollen-associated microbes may transfer resistance genes due to regular chemical interventions.The largest barrier to microbiome profiling using metagenomics is the limited accessibility of these methods due to high costs and the challenges associated with processing small amounts of DNA. However, ongoing methodological advances will enable more detailed and large-scale studies of pollen-associated microbial networks, ultimately supporting the development of greener, more resilient agricultural systems.IntensiveHuman-related environmental factors, such as agricultural practices, pollution, and urbanization modify communities (Obersteiner et al., 2016), and reduce microbial richness, potentially weakening the natural defense systems of crops. In plant protection strategies, protecting not only pollinators but also the microbial communities associated with crops should become a priority. Non-selective chemical pesticides can harm not only targeted pathogens but also beneficial microorganisms within the microbial community, leading to dysbiosis (i.e., an imbalance in the microbiome; Iebba et al., 2016). This can increase a plant's vulnerability to future pathogen infections and abiotic stresses. Therefore, after chemical treatments, the restoration of the microbiome could minimize microbial gaps that leave plants vulnerable to infection. Given that pollen extracts can stimulate fungal germination, they may also be harnessed to encourage the growth of beneficial microorganisms (Figure 1), offering a novel biocontrol strategy after considering the associated risks to the environment and human health. Moreover, a highly diverse production environment (e.g., cover crops), combined with the development of microbiome-friendly agricultural practices, promotes microbial abundance on pollen and plant surfaces.The largest barrier to microbiome profiling using metagenomics is the limited accessibility of these methods due to high costs and the challenges associated with processing small amounts of DNA. However, ongoing methodological advances will enable more detailed and large-scale studies of pollen-associated microbial networks, ultimately supporting the development of greener, more resilient agricultural systems.As final remarks, pollen--microbiome interactions are complex and crucial for plant health and agricultural sustainability. It is essential to recognize and include the modifying effect of pollen in pathogen--phyllosphere and microbiome interactions, as this perspective is critical for advancing both research and practical applications in agriculture. Preserving the diversity of plant-associated microbiomes on the phyllosphere is vital for crop health and resilience. In line with the One Health--One Biosecurity framework, future agricultural practices should focus on supporting microbiome-driven natural defenses rather than relying solely on pathogen control.