Land desertification poses a major ecological challenge and threatens agricultural productivity. This study investigated the seed endophytic microbiomes of desert plants as a potential resource for mitigating salt stress in crops. Using high-throughput sequencing, we characterized the bacterial and fungal communities within seeds of 12 desert plant species. Dominant taxa included Firmicutes (particularly Bacillus), Bacteroidota, Proteobacteria, Ascomycota, and Basidiomycota. Culturable bacteria were subsequently isolated from Haloxylon ammodendron (C.A.Mey.) Bunge (HB) and Hedysarum scoparium Fisch. & C.A.Mey. (HSA) seeds. These isolates were screened for plant growth-promoting (PGP) traits and tolerance to salt (NaCl) and alkali (NaHCO3). Selected strains, including the high indole-3-acetic acid (IAA)-producing Bacillus sp. HB-4, were used to inoculate wheat (Triticum aestivum L.) under 150 mM NaCl or 150 mM NaHCO3 stress. Inoculation with strain HB-4 significantly improved wheat growth under stress. This improvement was associated with increased chlorophyll and proline content, enhanced activities of the antioxidant enzymes catalase and peroxidase, and reduced levels of malondialdehyde, a marker of oxidative damage. Our results demonstrate that desert plant seeds harbor taxonomically distinct and functionally resilient endophytes. The successful application of a desert-adapted Bacillus strain to alleviate salt stress in wheat highlights the potential of such microbiomes as a novel source of inoculants for sustainable agriculture in saline-affected regions.