Since the first plant gene essential for arbuscular mycorrhizal (AM) symbiosis was identified, more than 170 such genes have been discovered. However, these findings remain scattered across species, and a systematic synthesis is urgently needed to guide future functional studies and breeding applications. This review provides a systematic classification and contextual overview of the currently reported plant genes essential for AM symbiosis, covering leguminous species (e.g., Medicago truncatula, Lotus japonicus) and non-leguminous species (e.g., Oryza sativa, Solanum lycopersicum). We classify these genes into functional modules corresponding to key stages of AM symbiosis: SL-mediated pre-symbiotic signaling, chitin signal perception, activation of the common symbiosis signaling pathway (CSSP), calcium (Ca²⁺) oscillation generation, arbuscule development and maintenance, and nutrient exchange. Beyond classification, we highlight conserved genetic modules across plant lineages and discuss their implications for engineering AM symbiosis in non-host or poorly symbiotic crops. This synthesis establishes a foundational genetic resource for molecular breeding aimed at enhancing nutrient-use efficiency and sustainable crop production.

Abies beshanzuensis M. H. Wu is a critically endangered conifer endemic to cool, high-elevation forests; its narrow range renders it vulnerable to climate warming and associated heat and water stress. We simulated climate warming by growing seedlings along an elevational gradient (500-1200 m) to assess physiological and molecular stress responses. Seedlings at mid-high elevation (1000-1200 m) grew optimally, whereas low-elevation (500 m) seedlings showed stress symptoms. At 500 m, Yield and ETR declined sharply; stomatal conductance also dropped, and NPQ collapsed entirely, dropping below the 1550 m baseline, proving quantitatively insufficient to prevent massive photoinhibition. Consequently, leaf chlorophyll content and biomass peaked at 1000 m and declined precipitously toward 500 m. Low-elevation leaves accumulated significantly higher levels of proline, soluble sugars, and proteins. However, this robust osmotic adjustment was physically insufficient to counteract the severe drought and heat stress, culminating in elevated MDA content and severe cellular damage. Antioxidant enzyme activities were highest at 1000 m and decreased at lower elevations. Transcriptome profiling and analysis of DEGs revealed altitude-dependent gene regulation. At 500 m, structural hub genes driving oxidative phosphorylation, glutathione metabolism, flavonoid biosynthesis (CSF7, MDMC, CHS), circadian rhythms, and heat-shock proteins were strongly upregulated. In contrast, genes for photosystems, primary hormone signaling, brassinosteroid biosynthesis, and pathogen defense were suppressed. Simulated warming induced pronounced stress responses, with photosynthesis and growth severely compromised, overwhelming osmotic adjustment and antioxidant defenses. These findings underscore the extreme climate vulnerability of A. beshanzuensis, establish 1000 m as a lower survival threshold, and highlight the urgent need to protect its high-elevation habitat and implement assisted conservation strategies.

Introduction: Abies beshanzuensis M. H. Wu is a critically endangered conifer species of immense ecological and evolutionary significance, with only three wild adult progenitor trees remaining globally. Due to its extreme vulnerability to environmental stress, poor natural regeneration, and obligate mycorrhizal dependency, identifying optimal microclimatic conditions for artificial cultivation is paramount for its survival. This study investigates how varying shading intensities influence the morpho-architectural, physiological, and transcriptomic responses of A. beshanzuensis seedlings to establish ideal conservation protocols. Methods: Seedlings were subjected to multiple shading treatments arrayed along an intensity gradient, culminating in extreme shading at T5. The intermediate treatment, T3, represented moderate shading. The experimental framework evaluated phenotypic morphology (plant height, crown width, and root system architecture), physiological parameters (leaf chlorophyll content, chlorophyll fluorescence, antioxidant enzyme activities, and oxidative stress markers), and osmotic adjustments. Furthermore, global transcriptome profiling utilizing advanced RNA-Seq methodologies coupled with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses was conducted to identify Differentially Expressed Genes (DEGs) and map regulatory molecular pathways. Results: Moderate shading (T3) profoundly enhanced plant height, crown width, root system architecture, and leaf chlorophyll content, significantly outperforming all other treatments. Root and shoot growth initially increased with shading intensity but declined sharply under excessive shading (T4 and T5). Chlorophyll fluorescence analysis demonstrated optimized photosynthetic performance under T3, characterized by higher electron transport rates and maximal photochemical efficiency, whereas extreme shading (T5) suppressed these parameters. Physiological assessments revealed that T3 seedlings exhibited the highest antioxidant enzyme activities (Superoxide Dismutase, Peroxidase, Catalase) and the lowest Malondialdehyde content, indicating minimal oxidative membrane damage. Soluble sugar, protein, and proline levels fluctuated, reflecting adaptive metabolic adjustments. Transcriptome analysis identified extensive DEGs across treatments, with significant enrichment in pathways related to photosynthesis, secondary metabolism, stress responses, and hormonal signaling. GO and KEGG analyses confirmed that T3 optimized energy metabolism, enhanced defense mechanisms, and differentially regulated hormone signal transduction. Discussion: Moderate shading (T3) establishes highly favorable environmental conditions for A. beshanzuensis by achieving a critical biological equilibrium between photosynthetic efficiency, stress resilience, and molecular regulation. Excessive shading disrupts this balance, precipitating carbon starvation and physiological decline. These findings illuminate the underlying regulatory networks of shade adaptation and provide a vital theoretical and practical foundation for the ex-situ conservation, and artificial cultivation of this critically endangered relict species.