Yuefei Xu

Hydrogen sulfide (H₂S) functions as a signaling molecule affecting plant growth, development, and stress adaptation. Tall fescue (Festuca arundinacea Schreb.), a bioenergy crop, encounters significant challenges in agricultural production owing to low light by shading. However, the influence of H₂S on tall fescue under low light stress (LLS) remains unclear. To examine the role of H₂S in acclimation of tall fescue to low light, we conducted combined analyses of physiological traits, metabolomics, and transcriptomics. These results showed that H₂S mitigated LLS‐induced inhibition of photosynthesis and maintained normal chloroplast ultrastructure by boosting the expression of photosynthesis‐related genes, including PsbQ, PsbR, PsaD, PsaK, and PetH, thereby enhancing the synthesis of carbohydrates (sucrose, starch). H₂S upregulated the expression of key genes (PFK, PK, IDH, G6PD) connected to glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway to promote carbon metabolism and ensure the supply of carbon skeletons and energy required for nitrogen metabolism. H₂S application reverted the LLS‐induced accumulation of nitrate nitrogen and the changes in the key nitrogen metabolism enzymes glutamate synthase (GOGAT, EC 1.4.1.13), nitrate reductase (NR, EC 1.6.6.1), glutamine synthetase (GS, EC 6.3.1.2), and glutamate dehydrogenase (GDH, EC 1.4.1.2), thus promoting amino acid decomposition to produce proteins involved in nitrogen assimilation and nitrogen use efficiency as well as specialized metabolism. Ultimately, H₂S upregulated the C/N ratio of tall fescue, balanced its carbon and nitrogen metabolism, enhanced shade tolerance, and increased biomass. These results provided new insights into enhancing plant resilience under LLS.

Elymus nutans Griseb. is a dominant forage in the Qinghai–Tibetan Plateau. However, the combined cold and drought (CD) stress is a major problem inhibiting its growth, development, and yield. Here, the responses of morphological, photosynthetic, osmoregulation levels, and signal transduction under cold, drought, and CD stress were explored. Both cold- and drought-stressed plants showed varying degrees of damage. In addition, CD stress led to more severe damage than single stress, especially in total biomass, photosynthetic capacity, and electron transfer efficiency. The total biomass, net photosynthetic rate, and maximal quantum yield of photosystem II (PSII) photochemistry reduced by 61.47%, 95.80%, and 16.06% in comparison with the control, respectively. Meanwhile, CD stress was accompanied by lower chlorophyll contents, down-regulated expression level of key photosynthetic enzymes (EnRbcS, EnRbcL, and EnRCA), stomatal closure, disrupted chloroplast ultrastructure, and reduced starch content. Furthermore, CD stress induced some adaptability responses in cold- and drought-tolerant E. nutans seedlings. The combined stress provoked alterations in both cold- and drought-related transcription factors and responsive genes. EnCBF12, EnCBF9, EnCBF14, and EnCOR14α were significantly up-regulated under cold or drought stress, and the transcript level of EnCBF3 and EnCBF12 was even 2.94 and 12.59 times higher than control under CD treatment, which indicated the key role of transcription factors activation in coping with CD stress. In addition, the content of soluble sugar, reducing sugar, proline, glycine betaine, and other osmolytes was significantly improved under CD stress. Therefore, we demonstrated that exposure to CD stress led to severe morphological and photosynthetic damage and revealed the acclimation to the cold and drought stress combination via osmotic adjustment and transcription factors activation in the Tibetan wild E. nutans.

Soil salinization is one of the most serious abiotic stresses restricting plant growth. Buffalograss is a C₄ perennial turfgrass and forage with an excellent resistance to harsh environments. To clarify the adaptative mechanisms of buffalograss in response to salinity, we investigated the effects of NaCl treatments on photosynthesis, water status and K⁺/Na⁺ homeostasis of this species, then analyzed the expression of key genes involved in these processes using the qRT-PCR method. The results showed that NaCl treatments up to 200 mM had no obvious effects on plant growth, photosynthesis and leaf hydrate status, and even substantially stimulated root activity. Furthermore, buffalograss could retain a large amount of Na⁺ in roots to restrict Na⁺ overaccumulation in shoots, and increase leaf K⁺ concentration to maintain a high K⁺/Na⁺ ratio under NaCl stresses. After 50 and 200 mM NaCl treatments, the expressions of several genes related to chlorophyll synthesis, photosynthetic electron transport and CO₂ assimilation, as well as aquaporin genes (BdPIPs and BdTIPs) were upregulated. Notably, under NaCl treatments, the increased expression of BdSOS1, BdHKT1 and BdNHX1 in roots might have helped Na⁺ exclusion by root tips, retrieval from xylem sap and accumulation in root cells, respectively; the upregulation of BdHAK5 and BdSKOR in roots likely enhanced K⁺ uptake and long-distance transport from roots to shoots, respectively. This work finds that buffalograss possesses a strong ability to sustain high photosynthetic capacity, water balance and leaf K⁺/Na⁺ homeostasis under salt stress, and lays a foundation for elucidating the molecular mechanism underlying the salt tolerance of buffalograss.

Hydrogen sulfide (H₂S) is an important gaseous signal molecule that regulates plant growth and stress resistance. However, research on the H₂S synthase (HSase) genes is still limited in the model legume plant Medicago truncatula Gaertn. In the present study, a total of 40 HSase family members were first identified and analyzed in the M. truncatula genome, and these genes distributed across eight chromosomes and were clustered into five groups (I–V) based on their conserved gene structures and protein motifs. Expression analysis revealed that the MtHSase genes were expressed in all the tested abiotic stresses, albeit with expression level differences. This study also showed that H₂S improves low temperature tolerance of alfalfa seedlings by regulating the antioxidant defense system and enhancing photosynthetic capacity. Thus, the study provides new insights into how the H₂S signal regulates tolerance to low‐temperature stress and provides the basis for further gene function and detection.

Soil salinity has become one of the major factors that threaten tall fescue growth and turf quality. Plants recruit diverse microorganisms in the rhizosphere to cope with salinity stress. In this study, 15 plant growth‐promoting rhizobacteria (PGPR) were isolated from the salt‐treated rhizosphere of tall fescue and were annotated to 10 genera, including Agrobacterium, Fictibacillus, Rhizobium, Bhargavaea, Microbacterium, Paenarthrobacter, Pseudarthrobacter, Bacillus, Halomonas, and Paracoccus. All strains could produce indole‐3‐acetic acid (IAA). Additionally, eight strains exhibited the ability to solubilize phosphate and potassium. Most strains could grow on the medium containing 600 mM NaCl, such as Bacillus zanthoxyli and Bacillus altitudinis. Furthermore, Bacillus zanthoxyli and Bacillus altitudinis were inoculated with tall fescue seeds and seedlings to determine their growth‐promoting effect. The results showed that Bacillus altitudinis and mixed culture significantly increased the germination rate of tall fescue seeds. Bacillus zanthoxyli can significantly increase the tillers number and leaf width of seedlings under salt conditions. Through the synergistic effect of FaSOS1, FaHKT1, and FaHAK1 genes, Bacillus zanthoxyli helps to expel the excess Na⁺ from aboveground parts and absorb more K⁺ in roots to maintain ion homeostasis in tall fescue. Unexpectedly, we found that Bacillus altitudinis displayed an inapparent growth‐promoting effect on seedlings under salt stress. Interestingly, the mixed culture of the two strains was also able to alleviate, to some extent, the effects of salt stress on tall fescue. This study provides a preliminary understanding of tall fescue rhizobacteria and highlights the role of Bacillus zanthoxyli in tall fescue growth and salt tolerance.