OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity

The cell wall functions in plant heavy metal response

Nonessential metals (e.g., cadmium (II), etc) and essential heavy metals (e.g., copper (II), etc) are both toxic for plants at high concentrations. The plant cell wall, which consists of pectin, cellulose, hemicellulose, lignin and proteins, acts as the first barrier for heavy metal ions to enter the cytoplasm. The binding of heavy metal ions within cell wall components is largely determined by the negative charges of functional groups. The cell wall interacts with heavy metal ions through three main mechanisms: ion exchange, chelation models and cell wall remodeling. Various signaling molecules such as nitric oxide and salicylic acid have been implicated in the regulation of cell wall components. An increasing number of reports indicate that microRNAs can target genes related with cell wall synthesis and modification, thereby mediating heavy metal fixation within the cell wall. In this review, we summarize recent advances in understanding the biosynthesis, modifications, and functions of cell wall components under heavy metal stress. We also discuss the interaction mechanisms and the signaling pathways involved in the cell wall-mediated fixation of heavy metals, offering valuable insights into plant heavy metal stress tolerance mechanisms and providing strategic avenues for mitigating heavy metal pollution.

Excessive copper induces lignin biosynthesis in the leaves and roots of two citrus species: Physiological, metabolomic and anatomical aspects

Excessive copper (Cu) of rhizosphere inhibited the growth and development of citrus seedlings. Lignin deposition on the cell wall promotes plant Cu tolerance. However, the lignin biosynthesis in citrus leaves and roots that respond to Cu toxicity is not fully understood. In this study, young seedlings of 'Xuegan' [Citrus sinensis (L.) Osbeck, a less Cu-tolerant species] and 'Shatian pomelo' [Citrus grandis (L.) Osbeck, a more Cu-tolerant species] were treated with nutrient solution containing 0.5 (as Control), 100, 300 or 500 µM Cu for 15 weeks in sandy culture. By the end of treatments, citrus leaves and roots were sampled to investigate the biomass allocation, Cu distribution, the lignin biosynthesis and deposition. The results indicated that Cu stress from 100 to 500 µM increased the root/shoot biomass ratio, promoting Cu and lignin accumulation in the leaves and roots of the tested citrus species. Besides, 300 µM Cu stress increased the accumulation of three lignin monomers of citrus species. The metabolomic profile indicated that Cu toxicity altered the lignin components of citrus species. The citrus roots are more prominent in the lignin precursor biosynthesis under Cu toxicity than citrus leaves. The histochemical staining supported that Cu stress improved the deposition of both guaiacy and syringy lignin units in citrus roots. The enzyme activity and gene expression revealed that activating lignin-biosynthetic enzymes, such as L-phenylalanine ammonia-lyase, peroxidase and laccase, played an essential role in lignin biosynthesis. Our results demonstrated that excessive Cu induced lignin biosynthesis in citrus leaves and roots to different extents. The findings from the present study increased our understanding of lignin biosynthesis in Cu-stressed citrus species, which would provide a theoretical basis for the citrus Cu-tolerant mechanisms.

The balance between alleviating copper damage and maintaining root function during root pruning with excessive copper

Coating high concentrations of copper (Cu) on the inner wall of containers can efficiently inhibit root entanglement of container-grown seedlings. However, how the protective and defensive responses of roots maintain root structure and function during Cu-root pruning is still unclear. Here, Duranta erecta L. seedlings were planted in the containers coated with 40 (T1), 80 (T2), 100 (T3), 120 (T4), 140 (T5) and 160 (T6) g L-1 Cu(OH)2 with containers without Cu(OH)2 as the control. Although T5 and T6 produced the best inhibitory effect on root entanglement, root anatomy structure was damaged. T1 and T2 not only failed to completely control root circling, but also led to decreased root activity and stunted growth. Cu(OH)2 treatments significantly increased lignin concentration of roots with the highest values at T3 and T4. Compared with T3, seedlings at T4 had higher height, biomass and root activity, and no significant root entanglement. Excessive Cu accumulation in Cu(OH)2 treatments changed the absorption of other mineral nutrients and their allocation in the roots, stems and leaves. Overall, Ca was decreased while Mg, Mn, Fe and K were increased, especially K and Mn at T4 which is related to defense capacity. The results indicate that there is a Cu threshold to balance root entanglement control, defense capacity and nutrient uptake function under excessive Cu for container-grown D. erecta seedlings.

Research Progress on Mechanical Strength of Rice Stalks

As one of the most important food crops in the world, rice yield is directly related to national food security. Lodging is one of the most important factors restricting rice production, and the cultivation of rice varieties with lodging resistance is of great significance in rice breeding. The lodging resistance of rice is directly related to the mechanical strength of the stalks. In this paper, we reviewed the cell wall structure, its components, and its genetic regulatory mechanism, which improved the regulatory network of rice stalk mechanical strength. Meanwhile, we analyzed the new progress in genetic breeding and put forward some scientific problems that need to be solved in this field in order to provide theoretical support for the improvement and application of rice breeding.

Comprehensive studies reveal physiological and genetic diversity in traditional rice cultivars for UV-B sensitivity

Acclimation to crop niches for thousands of years has made indigenous rice cultivars better suited for stress-prone environments. Still, their response to UV-B resiliency is unknown. 38 rice landraces were grown in cemented pots in a randomised block design with three replicates under open field conditions in Sambalpur University in the wet season of 2022. Half of the plants in each of the cultivars were administered UV-B radiation at the panicle emergence stage in an adjustable UV-B chamber permitting sunlight, and the effects of the stress on various morpho-physiological features, such as spikelet sterility, flag leaf photosynthetic and flavonoid pigment contents, and lipid peroxidation activities, were estimated for calibration of stress resistance. The experiment identified Swarnaprabha and Lalkain as the most sensitive and resilient to stress respectively, and the differential response between them was further revealed in the expression of genes related to UV-B sensitivity. Subject to the stress, Swarnaprabha exhibited symptoms of injuries, like leaf burns, and a higher loss of various photosynthetic parameters, such as pigment contents, SPAD and Fv/Fm, ETR and qP values, while NPQ increased only in Lalkain. Exposure to UV-B increased the total phenolic and flavonoid contents in Lalkain while depressing them in Swarnaprabha. Such an effect amounted to a higher release of fluorescent energy in the latter. The levels of expression of gene families controlling flavonoid activation and UV-B signal transduction, such as OsWRKY, OsUGT, OsRLCK, OsBZIP, OsGLP, and CPD photolyase were similar in both the cultivars in the control condition. However, exposure to UV-B stress overexpressed them in resilient cultivars only. The magnitude of expression of the genes and the impact of the stress on photosynthetic parameters, phenolic compounds and pubescent hair structure at the panicle emergence stage could be valid indicators among indigenous rice for UV-B tolerance.

Modifying lignin: A promising strategy for plant disease control

Lignin is a complex polymer found in the cell walls of plants, providing structural support and protection against pathogens. By modifying lignin composition and structure, scientists aim to optimize plant defense responses and increase resistance to pathogens. This can be achieved through various genetic engineering techniques which involve manipulating the genes responsible for lignin synthesis. By either up regulating or down regulating specific genes, researchers can alter the lignin content, composition, or distribution in plant tissues. Reducing lignin content in specific tissues like leaves can improve the effectiveness of defense mechanisms by allowing for better penetration of antimicrobial compounds. Overall, Lignin modification through techniques has shown promising results in enhancing various plants resistance against pathogens. Furthermore, lignin modification can have additional benefits beyond pathogen resistance. It can improve biomass processing for biofuel production by reducing lignin recalcitrance, making the extraction of sugars from cellulose more efficient. The complexity of lignin biosynthesis and its interactions with other plant components make it a challenging target for modification. Additionally, the potential environmental impact and regulatory considerations associated with genetically modified organisms (GMOs) require careful evaluation. Ongoing research aims to further optimize this approach and develop sustainable solutions for crop protection.

OsGLP8-7 interacts with OsPRX111 to detoxify excess copper in rice

Lignin is a phenolic biopolymer generated from phenylpropanoid pathway in the secondary cell wall and is required for defense of plants against various stress. Although the fact of stress-induced lignin deposition has been clearly demonstrated, it remains largely elusive how the formation of lignin is promoted under Cu stress. The present study showed that OsGLP8-7, an extracellular glycoprotein of rice (Oryza sativa L.), plays an important function against Cu stress. The loss function of OsGLP8-7 results in Cu sensitivity whereas overexpression of OsGLP8-7 scavenges Cu-induced superoxide anion (O2•-). OsGLP8-7 interacts with apoplastic peroxidase111 (OsPRX111) and elevates OsPRX111 stability when exposed to excess Cu. In OsGLP8-7 overexpressing (OE) lines, the retention of Cu within cell wall limiting Cu uptake into cytoplasm is attributed to the enhanced lignification required for Cu tolerance. Exogenous application of a lignin inhibitor can impair the Cu tolerance of transgenic Arabidopsis lines overexpressing OsGLP8-7. In addition, co-expression of OsGLP8-7 and OsPRX111 genes in tobacco leaves leads to an improved lignin deposition compared to leaves expressing each gene individually or the empty vector. Taken together, our findings provided the convincing evidences that the interaction between OsGLP8-7 and OsPRX111 facilitates effectively lignin polymerization, thereby contributing to Cu tolerance in rice.

Rice physical defenses and their role against insect herbivores

MAIN CONCLUSION

Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.

Divergent structures and functions of the Cupin proteins in plants

Cupin superfamily proteins have extensive functions. Their members are not only involved in the development of plants but also responded to various stresses. Whereas, the research on the Cupin members has not attracted enough attention. In this article, we summarized the research progress on these family genes in recent years and explored their evolution, structural characteristics, and biological functions. The significance of members of the Cupin family in the development of plant cell walls, roots, leaves, flowers, fruits, and seeds and their role in stress response are highlighted. Simultaneously, the prospective application of Cupin protein in crop enhancement was introduced. Some members can enhance plant growth, development, and resistance to adversity, thereby increasing crop yield. It will be as a foundation for future effective crop research and breeding.