CsiLAC4 modulates boron flow in Arabidopsis and Citrus via high-boron-dependent lignification of cell walls

MicroRNA gatekeepers: Orchestrating rhizospheric dynamics

The rhizosphere plays a crucial role in plant growth and resilience to biotic and abiotic stresses, highlighting the complex communication between plants and their dynamic rhizosphere environment. Plants produce a wide range of signaling molecules that facilitate communication with various rhizosphere factors, yet our understanding of these mechanisms remains elusive. In addition to protein-coding genes, increasing evidence underscores the critical role of microRNAs (miRNAs), a class of non-coding single-stranded RNA molecules, in regulating plant growth, development, and responses to rhizosphere stresses under diverse biotic and abiotic factors. In this review, we explore the crosstalk between miRNAs and their target mRNAs, which influence the development of key plant structures shaped by the belowground environment. Moving forward, more focused studies are needed to clarify the functions and expression patterns of miRNAs, to uncover the common regulatory mechanisms that mediate plant tolerance to rhizosphere dynamics. Beyond that, we propose that using artificial miRNAs and manipulating the expression of miRNAs and their targets through overexpression or knockout/knockdown approaches could effectively investigate their roles in plant responses to rhizosphere stresses, offering significant potential for advancing crop engineering.

Genome-wide identification, classification, and expression profiling of LAC gene family in sesame

BACKGROUND

Laccases (LACs) are vital plant growth and development enzymes, participating in lignin biopolymerization and responding to stress. However, the role of LAC genes in plant development as well as stress tolerance, is still not well understood, particularly in sesame (Sesamum indicum L.), an important oilseed crop.

RESULTS

In this study, 51 sesame LAC genes (SiLACs) were identified, which were unevenly distributed across different chromosomes. The phylogeny of Arabidopsis LAC (AtLACs) subdivided the SiLAC proteins into seven subgroups (Groups I-VII), of which Group VII contained only sesame LACs. Within the same subgroup, SiLACs exhibit comparable structures and conserved motifs. The promoter region of SiLACs harbors various cis-acting elements that are related to plant growth, phytohormones, and stress responses. Most SiLACs were expressed in the roots and stems, whereas some were expressed specifically in flowers or seeds. RNA-seq analysis revealed that 19 SiLACs exhibited down-regulation and three showed up-regulation in response to drought stress, while 15 SiLACs were down-regulated and four up-regulated under salt stress. Additionally, qRT-PCR analysis showcased that certain SiLAC expression was significantly upregulated as a result of osmotic and salt stress. SiLAC5 and SiLAC17 exhibited the most significant changes in expression under osmotic and salt stresses, indicating that they may serve as potential targets for improving sesame resistance to various stresses.

CONCLUSIONS

Our study offers a thorough comprehension of LAC gene structure, classification, evolution, and abiotic stress response in sesame plants. Furthermore, we provide indispensable genetic resources for sesame functional characterization to enhance its tolerance to various abiotic stresses.

CsLAC4, regulated by CsmiR397a, confers drought tolerance to the tea plant by enhancing lignin biosynthesis

Drought is a prevalent abiotic stress that commonly affects the quality and yield of tea. Although numerous studies have shown that lignin accumulation holds significant importance in conferring drought tolerance to tea plants, the underlying molecular regulatory mechanisms governing the tea plant's response to drought remain largely elusive. LACCASEs (LACs), which belong to the class of plant copper-containing polyphenol oxidases, have been widely reported to participate in lignin biosynthesis in plants and are implicated in numerous plant life processes, especially in the context of adverse conditions. In this study, we detected the upregulation of CsLAC4 in response to drought induction. Remarkably, the overexpression of CsLAC4 not only substantially increased the lignin content of transgenic Arabidopsis thaliana but also simulated the development of vascular tissues, consequently leading to a significant enhancement in drought tolerance. Moreover, via dual-luciferase assays and transient overexpression in tea leaves, we revealed that CsLAC4 was negatively regulated by the upstream CsmiR397a. Interestingly, the expression of CsmiR397a was downregulated during drought stress in tea plants. Arabidopsis thaliana overexpressing CsmiR397a showed increased sensitivity to drought stress. By transient overexpression of CsmiR397a and CsLAC4 in tea plant leaves, we verified that CsLAC4, which is regulated by CsmiR397a, conferred drought tolerance to tea plants by enhancing lignin biosynthesis. These findings enhance our understanding of the molecular regulatory mechanisms underlying the response of tea plants to drought stress.

Genome-Wide Identification and Characterization of the Laccase Gene Family in Fragaria vesca and Its Potential Roles in Response to Salt and Drought Stresses

Laccase (LAC, EC 1.10.3.2) is integral to the formation of lignin synthesis, flavonoid production, and responses to both biotic and abiotic stresses. While recent studies have characterized numerous LAC gene families and their functions across various plants, information regarding LAC genes in woodland strawberry (Fragaria vesca) remains limited. In this study, we identified a total of 57 FvLAC genes in the Fragaria vesca genome, which were phylogenetically categorized into five distinct groups. Analysis of the gene structures revealed a uniformity in the exon-intron structure among the subgroups, while conserved motifs identified unique motifs specific to certain subgroups, suggesting functional variations. Chromosomal localization studies indicated that FvLACs are distributed across seven chromosomes, and collinearity analysis demonstrated that FvLACs exhibit collinearity within the species. Additionally, cis-acting element analysis suggested that FvLAC genes are involved in stress responses, hormone responses, light responses, and the growth and development of plants. qRT-PCR demonstrated that FvLACs responded to salt, drought, and hormone stresses, with the expression levels of FvLAC24, FvLAC32, and FvLAC51 continuously increasing under these stress conditions. Furthermore, transgenic yeast experiments revealed that FvLAC51 enhanced yeast tolerance to both salt and drought stresses, while FvLAC24 and FvLAC32 negatively regulated yeast tolerance under these same conditions. These findings provide a theoretical foundation for further investigation into the functions of FvLAC genes in woodland strawberry.

Mechanisms by Which Increased pH Ameliorates Copper Excess in Citrus sinensis Roots: Insight from a Combined Analysis of Physiology, Transcriptome, and Metabolome

Limited data are available on copper (Cu)-pH interaction-responsive genes and/or metabolites in plant roots. Citrus sinensis seedlings were treated with 300 μM (Cu toxicity) or 0.5 μM (control) CuCl2 at pH 3.0 or 4.8 for 17 weeks. Thereafter, gene expression and metabolite profiles were obtained using RNA-Seq and widely targeted metabolome, respectively. Additionally, several related physiological parameters were measured in roots. The results indicated that elevating the pH decreased the toxic effects of Cu on the abundances of secondary metabolites and primary metabolites in roots. This difference was related to the following several factors: (a) elevating the pH increased the capacity of Cu-toxic roots to maintain Cu homeostasis by reducing Cu uptake and Cu translocation to young leaves; (b) elevating the pH alleviated Cu toxicity-triggered oxidative damage by decreasing reactive oxygen species (ROS) formation and free fatty acid abundances and increasing the ability to detoxify ROS and maintain cell redox homeostasis in roots; and (c) increasing the pH prevented root senescence and cell wall (CW) metabolism impairments caused by Cu toxicity by lowering Cu levels in roots and root CWs, thus improving root growth. There were some differences and similarities in Cu-pH interaction-responsive genes and metabolites between leaves and roots.

Genome-wide identification and expressional analysis of carotenoid cleavage oxygenase (CCO) gene family in Betula platyphylla under abiotic stress

BACKGROUND

Carotenoid cleavage oxygenases (CCOs) are a group of enzymes that catalyze the oxidative cleavage of carotenoid molecules. These enzymes widely exist in plants, fungi, and certain bacteria, and are involved in various biological processes. It would be of great importance and necessity to identify CCO members in birch and characterize their responses upon abiotic stresses.

RESULTS

A total of 16 BpCCOs, including 8 BpCCDs and 8 BpNCEDs were identified in birch, and phylogenetic tree analysis showed that they could be classified into six subgroups. Collinearity analysis revealed that BpCCOs have the largest number of homologous genes in Gossypium hirsutum and also have more homologous genes in other dicotyledons. In addition, promoter analysis revealed that the promoter regions of BpCCOs contained many abiotic stress-related and hormone-responsive elements. The results of qRT-PCR showed that most of the BpCCOs were able to respond significantly to ABA, PEG, salt and cold stresses. Finally, the prediction of the interacting proteins of BpCCOs by STRING revealed several proteins that may interact with BpCCOs and be involved in plant growth and development/abiotic stress processes, such as HEC1 (bHLH), ATABA1, ATVAMP714, etc. CONCLUSION: In this study, the CCO members were identified in birch in a genome-wide scale. These results indicate that BpCCO genes may play important roles in the abiotic stress responses of birch plants.

miR397 regulates cadmium stress response by coordinating lignin polymerization in the root exodermis in Kandelia obovata

Secondary lignification of the root exodermis of Kandelia obovata is crucial for its response to adversity such as high salinity and anaerobic environment, and this lignification is also effective in blocking cadmium transport to the roots. However, how the differences in lignification of root exodermis at different developmental stages respond to Cd stress and its regulatory mechanisms have not been revealed. In this study, after analyzing the root structure and cell wall thickness using a Phenom scanning electron microscope as well as measuring cadmium content in the root cell wall, we found that the exodermis of young and mature roots of K. obovata responded to Cd stress through the polymerization of different lignin monomers, forming two different mechanisms: chelation and blocking. Through small RNA sequencing, RLM-5'-RACE and dual luciferase transient expression system, we found that miR397 targets and regulates KoLAC4/17/7 expression. The expression of KoLAC4/17 promoted the accumulation of guaiacyl lignin during lignification and enhanced the binding of cadmium to the cell wall. Meanwhile, KoLAC7 expression promotes the accumulation of syringyl lignin during lignification, which enhances the obstruction of cadmium and improves the tolerance to cadmium. These findings enhance our understanding of the molecular mechanisms underlying the differential lignification of the root exodermis of K. obovata in response to cadmium stress, and provide scientific guidance for the conservation of mangrove forests under heavy metal pollution.

The CsmiR397a-CsLAC17 module regulates lignin biosynthesis to balance the tenderness and gray blight resistance in young tea shoots

Lignin accumulation can enhance the disease resistance of young tea shoots (Camellia sinensis). It also greatly reduces their tenderness, which indirectly affects the quality and yield of tea. Therefore, the regulation of lignin biosynthesis appears to be an effective way to balance tenderness and disease resistance in young tea shoots. In this study, we identified a laccase gene, CsLAC17, that is induced during tenderness reduction and gray blight infection in young tea shoots. Overexpression of CsLAC17 significantly increased the lignin content in transgenic Arabidopsis, enhancing their resistance to gray blight and decreasing stem tenderness. In addition, we found that CsLAC17 was negatively regulated by the upstream CsmiR397a by 5'-RLM-RACE, dual-luciferase assay, and transient expression in young tea shoots. Interestingly, the expression of CsmiR397a was inhibited during tenderness reduction and gray blight infection of young tea shoots. Overexpression of CsmiR397a reduced lignin accumulation, resulting in decreased resistance to gray blight and increased stem tenderness in transgenic Arabidopsis. Furthermore, the transient overexpression of CsmiR397a and CsLAC17 in tea leaves directly confirms the function of the CsmiR397a-CsLAC17 module in lignin biosynthesis and its effect on disease resistance. These results suggest that the CsmiR397a-CsLAC17 module is involved in balancing tenderness and gray blight resistance in young tea shoots by regulating lignin biosynthesis.

Contribution of the LAC Genes in Fruit Quality Attributes of the Fruit-Bearing Plants: A Comprehensive Review

Laccase genes produce laccase enzymes that play a crucial role in the production of lignin and oxidation reactions within plants. Lignin is a complex polymer that provides structure and toughness to the cell walls of numerous fruit plants. The LAC genes that encode laccase enzymes play vital roles in plant physiology, including the synthesis of pigments like PA that contribute to the colors of fruits, and in defending against pathogens and environmental stresses. They are crucial for fruit development, ripening, structural maintenance in plants, and adaptation to various environmental factors. As such, these genes and enzymes are essential for plant growth and development, as well as for various biotechnological applications in environmental remediation and industrial processes. This review article emphasizes the significance of genes encoding laccase enzymes during fruit growth, specifically pertaining to the strengthening of the endocarp through lignification. This process is crucial for ensuring fruit defense and optimizing seed scattering. The information gathered in this article will aid breeders in producing future fruit-bearing plants that are resistant to disease, cost-effective, and nutrient-rich.

A critical review of plant adaptation to environmental boron stress: Uptake, utilization, and interplay with other abiotic and biotic factors

Boron (B) is an indispensable mineral nutrient for plants and is primarily taken up by roots mainly in the form of boric acid (H3BO3). Recently, research shows that B has a significant impact on plant growth and productivity due to its narrow range between deficiency and toxicity. Fertilization and other procedures to address B stress (deficiency and toxicity) in soils are generally expensive and time-consuming. Over the past 20 years, substantial studies have been conducted to investigate the mechanisms underlying B acquisition and the molecular regulation of B stress in plants. In this review, we discuss the effects of B stress on plant growth, physiology, and biochemistry, and finding on enhancing plant tolerance from the perspective of plant B uptake, transport, and utilization. We also refer to recent results demonstrating the interactions among B and other biological and abiotic factors, including nitrogen, phosphorus, aluminum, and microorganisms. Finally, emerging trends in this field are discussed.

The PcMYB44-mediated miR397-PcLACs module regulates defence-induced lignification in pear resistance to fungal disease

Diseases caused by Alternaria alternata and Botryosphaeria dothidea diminish pear yield and quality, and restrict the pear agricultural industry. Lignification is a conserved mechanism for plant resistance against pathogen invasion. The regulatory mechanisms underlying defence-induced lignification in pear in response to fungal pathogen infection remain unknown. In this study, analysis of lignification level and lignin content in pear revealed that A. alternata and B. dothidea induced lignification, and transcriptomics showed that lignin biosynthesis was affected. To explore whether laccases (LACs) mediated by miR397 regulate lignification in pear, we investigated the role of PcmiR397 in repressing the expression of PcLACs using 5'-RNA ligase-mediated-RACE and co-transformation in tobacco. Opposite expression patterns for PcmiR397 and PcLAC target genes were observed in pear in response to pathogens. Transient transformation in pear demonstrated that silencing PcmiR397 and overexpressing a single PcLAC enhanced resistance to pathogens via lignin synthesis. To further reveal the mechanism underpinning the PcMIR397 response of pear to pathogens, the PcMIR397 promoter was analysed, and pMIR397-1039 was found to be inhibited by pathogen infection. The transcription factor PcMYB44 was up-regulated, and it bound to the PcMIR397 promoter and inhibited transcription following pathogen infection. The results demonstrate the role of PcmiR397-PcLACs in broad-spectrum resistance to fungal disease, and the potential role of PcMYB44 involved in the miR397-PcLAC module in regulating defence-induced lignification. The findings provide valuable candidate gene resources and guidance for molecular breeding to improve resistance to fungal disease in pear.

Physiological and iTRAQ-based quantitative proteomics analyses reveal the similarities and differences in stress responses between short-term boron deficiency and toxicity in wheat roots

BACKGROUND

Boron (B) is a trace element that is essential for normal wheat development, such as root growth. In wheat, roots are important organs that absorb nutrients and water. However, at present, there is insufficient research on the molecular mechanism underlying how short-term B stress affects wheat root growth.

METHODS AND RESULTS

Here, the optimal concentration of B for wheat root growth was determined, and the proteomic profiles of roots under short-term B deficiency and toxicity were analyzed and compared by the isobaric tag for relative and absolute quantitation (iTRAQ) technique. A total of 270 differentially abundant proteins (DAPs) that accumulated in response to B deficiency and 263 DAPs that accumulated in response to B toxicity were identified. Global expression analysis revealed that ethylene, auxin, abscisic acid (ABA), and Ca2+ signals were involved in the responses to these two stresses. Under B deficiency, DAPs related to auxin synthesis or signaling and DAPs involved in calcium signaling increased in abundance. In striking contrast, auxin and calcium signals were repressed under B toxicity. Twenty-one DAPs were detected under both conditions, including RAN1 that played a core role in the auxin and calcium signals. Overexpression of RAN1 was shown to confer plant resistance to B toxicity by activating auxin response genes, including TIR and those identified by iTRAQ in this research. Moreover, growth of the primary roots of tir mutant was significantly inhibited under B toxicity.

CONCLUSION

Taken together, these results indicate that some connections were present between RAN1 and the auxin signaling pathway under B toxicity. Therefore, this research provides data for improving the understanding of the molecular mechanism underlying the response to B stress.

Characterization of plant laccase genes and their functions

Laccase is a copper-containing polyphenol oxidase found in different organisms. The multigene family that encodes laccases is widely distributed in plant genomes. Plant laccases oxidize monolignols to produce lignin which is important for plant growth and stress responses. Industrial applications of fungal and bacterial laccases are extensively explored and addressed. Recently many studies have focused on the significance of plant laccase, particularly in crop yield, and its functions in different environmental conditions. This review summarizes the transcriptional and posttranscriptional regulation of plant laccase genes and their functions in plant growth and development. It especially describes the responses of laccase genes to various stresses and their contributions to plant biotic and abiotic stress resistance. In-depth explanations and scientific advances will serve as foundations for research into plant laccase genes' function, mechanism, and possible applications.

The Citrus Laccase Gene CsLAC18 Contributes to Cold Tolerance

Plant laccases, as multicopper oxidases, play an important role in monolignol polymerization, and participate in the resistance response of plants to multiple biotic/abiotic stresses. However, little is currently known about the role of laccases in the cold stress response of plants. In this study, the laccase activity and lignin content of C. sinensis leaves increased after the low-temperature treatment, and cold treatment induced the differential regulation of 21 CsLACs, with 15 genes being upregulated and 6 genes being downregulated. Exceptionally, the relative expression level of CsLAC18 increased 130.17-fold after a 48-h treatment. The full-length coding sequence of CsLAC18 consists of 1743 nucleotides and encodes a protein of 580 amino acids, and is predominantly expressed in leaves and fruits. CsLAC18 was phylogenetically related to AtLAC17, and was localized in the cell membrane. Overexpression of CsLAC18 conferred enhanced cold tolerance on transgenic tobacco; however, virus-induced gene silencing (VIGS)-mediated suppression of CsLAC18 in Poncirus trifoliata significantly impaired resistance to cold stress. As a whole, our findings revealed that CsLAC18 positively regulates a plant's response to cold stress, providing a potential target for molecular breeding or gene editing.

Identification of Competing Endogenous RNAs (ceRNAs) Network Associated with Drought Tolerance in Medicago truncatula with Rhizobium Symbiosis

Drought, bringing the risks of agricultural production losses, is becoming a globally environmental stress. Previous results suggested that legumes with nodules exhibited superior drought tolerance compared with the non-nodule group. To investigate the molecular mechanism of rhizobium symbiosis impacting drought tolerance, transcriptome and sRNAome sequencing were performed to identify the potential mRNA-miRNA-ncRNA dynamic network. Our results revealed that seedlings with active nodules exhibited enhanced drought tolerance by reserving energy, synthesizing N-glycans, and medicating systemic acquired resistance due to the early effects of symbiotic nitrogen fixation (SNF) triggered in contrast to the drought susceptible with inactive nodules. The improved drought tolerance might be involved in the decreased expression levels of miRNA such as mtr_miR169l-5p, mtr_miR398b, and mtr_miR398c and its target genes in seedlings with active nodules. Based on the negative expression pattern between miRNA and its target genes, we constructed an mRNA-miR169l-ncRNA ceRNA network. During severe drought stress, the lncRNA alternative splicings TCONS_00049507 and TCONS_00049510 competitively interacted with mtr_miR169l-5p, which upregulated the expression of NUCLEAR FACTOR-Y (NF-Y) transcription factor subfamily NF-YA genes MtNF-YA2 and MtNF-YA3 to regulate their downstream drought-response genes. Our results emphasized the importance of SNF plants affecting drought tolerance. In conclusion, our work provides insight into ceRNA involvement in rhizobium symbiosis contributing to drought tolerance and provides molecular evidence for future study.

Citrus Physiological and Molecular Response to Boron Stresses

Since the essentiality of boron (B) to plant growth was reported nearly one century ago, the implication of B in physiological performance, productivity and quality of agricultural products, and the morphogenesis of apical meristem in plants has widely been studied. B stresses (B deficiency and toxicity), which lead to atrophy of canopy and deterioration of Citrus fruits, have long been discovered in citrus orchards. This paper reviews the research progress of B stresses on Citrus growth, photosynthesis, light use efficiency, nutrient absorption, organic acid metabolism, sugar metabolism and relocation, and antioxidant system. Moreover, the beneficial effects of B on plant stress tolerance and further research in this area were also discussed.