Five Conserved microRNAs Dominate the Small-RNA Pool of Three Arid-Zone Camel-Forage Plants: De Novo Repertoires and a Species-Matched Test of Cross-Kingdom Targeting in the Dromedary.

Background: Camel husbandry underpins food security in drylands, and dromedary (Camelus dromedarius) milk is valued as a functional food whose composition is thought to be shaped by the desert forage that camels browse. Dietary plant microRNAs (miRNAs) have been proposed as one molecular route linking diet to mammalian physiology, and two interactions are widely cited from experimental reports: rice miR168a repressing LDLRAP1 and plant miR159 repressing TCF7. The hypothesis remains contested, however, and it has not been tested for camel forage against camel transcripts. Methods: We generated de novo, hairpin-based miRNA repertoires for three arid-zone forage plants relevant to camel feeding (Moringa oleifera, Ziziphus jujuba, Medicago sativa) and screened the mature miRNAs against 48,746 reconstructed C. dromedarius 3'-UTRs under stringent thresholds, retaining one transcript per gene, weighting interactions by read abundance, normalising scores for 3'-UTR length, and testing over-representation against a matched background. The two previously reported cross-kingdom pairs served as internal positive controls and seed-level grouping as a sensitivity control. Results: The three forages yielded 170 hairpin-validated miRNA loci (81 M. sativa, 49 Z. jujuba, 40 M. oleifera) peaking at 21 nt, collapsing to 116 mature sequences and 104 seed groups. The pooled read set was strongly concentrated: five mature sequences shared by all three species carried 51% of reads, miR159 alone 31%, and 19 sequences assignable to conserved miRBase families carried 64%. The pipeline recovered the reported miR168a-LDLRAP1 pairing in the camel; the miR159-TCF7 pairing, by contrast, was not recovered, although TCF7 was among the genes targeted by other plant miRNAs. Genome-wide, predicted targeting was sparse (median 2 miRNAs per gene) and no GO, KEGG or Hallmark category was enriched at either threshold (best FDR 0.56); the nominal p-value distribution was approximately uniform, giving no evidence of systematic enrichment under the tested framework. Targeting multiplicity scaled with 3'-UTR length (Pearson r = 0.63; Spearman ρ = 0.58), so apparent "hub" genes are largely long-3'-UTR genes. Of 19, 12 curated milk-fat and lactation genes were among predicted targets, without over-representation (Fisher p = 0.36). Conclusions: A sensitive, species-matched analysis recovered a previously reported cross-kingdom pairing yet found no coordinated enrichment of dietary plant miRNAs on the dromedary transcriptome, and showed that an individual cross-kingdom pairing cannot be assumed to transfer between mammalian species. The work provides a first forage miRNA resource in the context of camel nutrition, sets out a reusable, species-matched analytical framework for cross-kingdom claims, and narrows future experimental work to five abundant forage-derived sequences and a short list of candidate genes (LDLRAP1, TCF7/TCF7L2, PRLR, INSR).