**1. Introduction**

Amaryllidaceae species have been utilized as vegetables, herbs, spices, and ornamentals in all continents since ancient times. Many of them have shown widespread benefits in cuisine and healing of common diseases like atherosclerosis, diabetes, inflammation, hypertension, and cancer. These protective effects appear to be related to the presence of organosulfur compounds, predominantly allyl derivatives in Allioidae and alkaloids in the Amaryllidoidae subfamily [1]. The economic significance of Amaryllidaceae crops is substantiated by the all-year-round supply and a wide range of cultivars and landraces characterized by plant parts with different shapes and specific taste and flavor. The biochemical profile of plants determines a broad or specialized usage by food and pharmacological

industry [2–4]. Considering the wide distribution, unique chemical composition, and economic importance, we selected Amaryllidaceae crops to analyze their relationship with the microbiome colonizing the root and shoot tissues.

With regard to root fungal microbiome, Amaryllidaceae symbiosis with arbuscular mycorrhizal fungi has been widely investigated at the physiological, biochemical, and genetic level, and it has been comprehensively reviewed [5–8]. However, there is selective and narrow knowledge of fungal endophytes colonizing these plants. Hardoim et al. [9] defined "endophytes" as microorganisms living in plant tissues in some periods of their life cycle or all through, so the word is referred to the habitat rather than function. Nevertheless, endophytic fungi live inside the tissues of apparently healthy and asymptomatic hosts. The case of Amaryllidaceae crops can help in understanding how fungal endophytes modulate the physiological processes in the above- and below-ground plant tissues as well as interact with a host plant and with other microbes. The effect of plant morphology on colonization and biodiversity of endophyte communities has been rarely studied. The root-associated fungi play an important role in plant nutrition by: mobilizing soil nutrients; recycling organic matter; increasing the water holding capacity and absorption; protecting against pathogens and abiotic stresses; biosynthesizing lignan, auxins, and ethylene, in order to improve the root system expansion and encourage plant fitness through thermotolerance improvement; and coping with salinity, drought, and heavy metal stress [10,11]. The underground bulb has been an additional component of plant tissue/endophyte puzzles as a perennial storage part rich in nutrient compounds, and—in some taxons containing unique bioagents—Amaryllidaceae alkaloids. Taking into account their life cycle, Amaryllidaceae have to efficiently allocate resources from bulbs to vegetative and generative tissues and vice versa during a short vegetation period. It is possible that the assimilates' flow provides a natural path for plants to partitioning the symbiotic endophytes as it was proposed for mycorrhizal fungi by Cri¸san et al. [12]. Foliar endophytes can stimulate host plant biomass, yield, mineral status, nutritive value, stomatal movement, and defensive mutualism against herbivores and pathogens [13,14].

The strict selection and recruitment of the endophytes by a host species was postulated and analyzed for plant-associated bacteria [15] but the mentioned mechanisms also shape fungal diversity and abundance [16]. The rhizoplane and phylloplane are considered to be a selective gate for endophytes, mediating dynamic changes in the fungal community in plant internal tissues. This is the reason for differences in microbial compositions among host species and even among their tissues [8]. Plant secondary metabolites are postulated as main regulators in colonization and development of fungal endophytes in different tissues and, vice versa, fungal metabolites can play a similar role with respect to the host and the microbiota [17,18]. Plant secondary metabolites are postulated as main regulators in colonization and development of fungal endophytes in different tissues and, vice versa, fungal metabolites can play a similar role with respect to the host and the microbiota [19]. Bioactive metabolites synthesized by fungal endophytes show multidirectional actions in plants and can be explored for the cultivation of targeted functional and medicinal crops [20]. Nowadays, endophytes are also recognized as an alternative to synthetic chemicals in crop production and protection [21]. However, to be successfully applied, endophytes need specific conditions for efficient host tissue colonization. This can be achieved by a thorough understanding of the endophyte-host relationship starting from the colonization up to well-established symbiosis, on the basis of the fungi and plant biology, covering genetic and biochemical factors as well [22–24].

This review aimed to analyze fungal endophyte communities associated with Amaryllidaceae crops, by: presenting the evidence of ubiquitous and/or species- and tissue-dependent fungal microbiome, reviewing the known chemical compounds synthesized by fungal endophytes, and emphasizing their possible vital effects on human proecological and prohealth activities.
