Sulfur (S) is an essential macronutrient for plant growth and development. S is majorly absorbed as sulfate from soil, and is then translocated to plastids in leaves, where it is assimilated into organic products. Cysteine (Cys) is the first organic product generated from S, and it is used as a precursor to synthesize many S-containing metabolites with important biological functions, such as glutathione (GSH) and methionine (Met). The reduction of sulfate takes place in a two-step reaction involving a variety of enzymes. Sulfate transporters (SULTRs) are responsible for the absorption of SO₄²⁻ from the soil and the transport of SO₄²⁻ in plants. There are 12–16 members in the S transporter family, which is divided into five categories based on coding sequence homology and biochemical functions. When exposed to S deficiency, plants will alter a series of morphological and physiological processes. Adaptive strategies, including cis-acting elements, transcription factors, non-coding microRNAs, and phytohormones, have evolved in plants to respond to S deficiency. In addition, there is crosstalk between S and other nutrients in plants. In this review, we summarize the recent progress in understanding the mechanisms underlying S homeostasis in plants.

Iron (Fe) is an essential element required for plant growth and development. Under Fe-deficientconditions, plants have developed two distinct strategies (designated as strategy I and II) to acquire Fe from soil. As a graminaceous species, rice is not a typical strategy II plant, as it not only synthesizes DMA (2’-deoxymugineic acid) in roots to chelate Fe³⁺ but also acquires Fe²⁺ through transporters OsIRT1 and OsIRT2. During the synthesis of DMA in rice, there are three sequential enzymatic reactions catalyzed by enzymes NAS (nicotianamine synthase), NAAT (nicotianamine aminotransferase), and DMAS (deoxymugineic acid synthase). Many transporters required for Fe uptake from the rhizosphere and internal translocation have also been identified in rice. In addition, the signaling networks composed of various transcription factors (such as IDEF1, IDEF2, and members of the bHLH (basic helix-loop-helix) family), phytohormones, and signaling molecules are demonstrated to regulate Fe uptake and translocation. This knowledge greatly contributes to our understanding of the molecular mechanisms underlying iron deficiency responses in rice.

Auxin regulates plant growth and development, as well as helps plants to survive abiotic stresses, but the effects of auxin on the growth of alkaline-stressed rice and the underlying molecular and physiological mechanisms remain unknown. Through exogenous application of IAA/TIBA, this study explored the physiological and molecular mechanisms of alkaline stress tolerance enhancement using two rice genotypes. Alkaline stress was observed to damage the plant growth, while exogenous application of IAA mitigates the alkaline-stress-induce inhibition of plant growth. After application of exogenous IAA to alkaline-stressed rice, dry shoot biomass, foliar chlorophyll content, photosynthetic rate in the two rice genotypes increased by 12.6–15.6%, 11.7–40.3%, 51.4–106.6%, respectively. The adventitious root number, root surface area, total root length and dry root biomass in the two rice genotypes increased by 29.3–33.3%, 26.4–27.2%, 42.5–35.5% and 12.8–33.1%, respectively. The accumulation of H₂O₂, MAD were significantly decreased with the application of IAA. The activities of CAT, POD, and SOD in rice plants were significantly increased by exogenous application of IAA. The expression levels of genes controlling IAA biosynthesis and transport were significantly increased, while there were no significant effects on the gene expression that controlled IAA catabolism. These results showed that exogenous application of IAA could mitigate the alkaline-stress-induced inhibition of plant growth by regulating the reactive oxygen species scavenging system, root development and expression of gene involved in IAA biosynthesis, transport and catabolism. These results provide a new direction and empirical basis for improving crop alkaline tolerance with exogenous application of IAA.

Saline–alkaline stress suppresses rice growth and threatens crop production. Despite substantial research on rice’s tolerance to saline–alkaline stress, fewer studies have examined the impact of magnetic water treatments on saline–alkaline-stressed rice plants. We explored the physiological and molecular mechanisms involved in saline–alkaline stress tolerance enhancement via irrigation with magnetized water using Nipponbare. The growth of Nipponbare plants was inhibited by saline–alkaline stress, but this inhibition was alleviated by irrigating the plants with magnetized water, as evidenced by greater plant height, biomass, chlorophyll content, photosynthetic rates, and root system in plants irrigated with magnetized water compared to those irrigated with non-magnetized water. Plants that were irrigated with magnetized water were able to acquire more total nitrogen. In addition, we proved that rice seedlings irrigated with magnetized water had a greater root NO₃⁻-nitrogen concentration and root NH₄⁺-nitrogen concentration than plants irrigated with non-magnetized water. These findings suggest that treatment with magnetized water could increase nitrogen uptake. To test this hypothesis, we analyzed the expression levels of genes involved in nitrogen acquisition. The expression levels of OsNRT1;1, OsNRT1;2, OsNRT2;1, OsAMT1;2, OsAMT2;1, OsAMT2;2, OsAMT2;3, OsAMT3;1, OsAMT3;2, and OsAMT3;3 were higher in plants exposed to magnetized water medium compared to those exposed to non-magnetized water media. We further demonstrated that treatment with magnetized water increases available nitrogen, NO₃⁻-nitrogen content, and NH₄⁺-nitrogen content in soil under saline–alkaline stress. Our results revealed that the increased resistance of rice seedlings to saline–alkaline stress may be attributable to a very effective nitrogen acquisition system enhanced by magnetized water.

Saline-alkaline stress is an abiotic stress that suppresses rice plant growth and reduces yield. However, few studies have investigated the mechanism by which rice plants respond to saline-alkaline stress at a global transcriptional level. Dongdao-4 and Jigeng-88, which differ in their tolerance to saline-alkaline stress, were used to explore gene expression differences under saline-alkaline stress by RNA-seq technology. In seedlings of Dongdao-4 and Jigeng-88, 3523 and 4066 genes with differential levels of expression were detected, respectively. A total of 799 genes were upregulated in the shoots of both Dongdao-4 and Jigeng-88, while 411 genes were upregulated in the roots of both genotypes. Among the downregulated genes in Dongdao-4 and Jigeng-88, a total of 453 and 372 genes were found in shoots and roots, respectively. Gene ontology (GO) analysis showed that upregulated genes were enriched in several GO terms such as response to stress, response to jasmonic acid, organic acid metabolic process, nicotianamine biosynthetic process, and iron homeostasis. The downregulated genes were enriched in several GO terms, such as photosynthesis and response to reactive oxygen species. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that Dongdao-4 seedlings were specifically enriched in the biosynthesis of secondary metabolites such as diterpenoids and phenylpropanoids. The upregulated genes that were involved in secondary metabolite biosynthesis, amino acid biosynthesis, betalain biosynthesis, organic acid metabolic process, and iron homeostasis pathways may be central to saline-alkaline tolerance in both rice genotypes. In contrast, the genes involved in the diterpenoid and phenylpropanoid biosynthesis pathways may contribute to the greater tolerance to saline-alkaline stress in Dongdao-4 seedlings than in Jigeng-88. These results suggest that Dongdao-4 was equipped with a more efficient mechanism involved in multiple biological processes to adapt to saline-alkaline stress.

Bromus inermis L. (commonly known as smooth bromegrass) is a grass species with high nutritional value, great palatability, cold tolerance, and grazing resistance, which has been widely cultivated for pasture and sand fixation in northern and northwestern China. Salt stress is a main environmental factor limiting growth and production of smooth bromegrass. In this study, we performed PacBio Iso-Seq to construct the first full-length transcriptome database for smooth bromegrass under 300 mM NaCl treatment at different time points. Third-generation full-length transcriptome sequencing yielded 19.67 G polymerase read bases, which were assembled into 355,836 full-length transcripts with an average length of 2,542 bp. A total of 116,578 differentially expressed genes were obtained by comparing the results of third-generation sequencing and second-generation sequencing. GO and KEGG enrichment analyses revealed that multiple pathways were differently activated in leaves and roots. In particular, a number of genes participating in the molecular network of plant signal perception, signal transduction, transcription regulation, antioxidant defense, and ion regulation were affected by NaCl treatment. In particular, the CBL-CIPK, MAPK, ABA signaling network, and SOS core regulatory pathways of Ca²⁺ signal transduction were activated to regulate salt stress response. In addition, the expression patterns of 10 salt-responsive genes were validated by quantitative real-time PCR, which were consistent with those detected by RNA-Seq. Our results reveal the molecular regulation of smooth bromegrass in response to salt stress, which are important for further investigation of critical salt responsive genes and molecular breeding of salt-tolerant smooth bromegrass.