Manganese (Mn) is an essential element for plant growth due to its participation in a series of physiological and metabolic processes. Mn is also considered a heavy metal that causes phytotoxicity ...when present in excess, disrupting photosynthesis and enzyme activity in plants. Thus, Mn toxicity is a major constraint limiting plant growth and production, especially in acid soils. To cope with Mn toxicity, plants have evolved a wide range of adaptive strategies to improve their growth under this stress. Mn tolerance mechanisms include activation of the antioxidant system, regulation of Mn uptake and homeostasis, and compartmentalization of Mn into subcellular compartments (e.g., vacuoles, endoplasmic reticulum, Golgi apparatus, and cell walls). In this regard, numerous genes are involved in specific pathways controlling Mn detoxification. Here, we summarize the recent advances in the mechanisms of Mn toxicity tolerance in plants and highlight the roles of genes responsible for Mn uptake, translocation, and distribution, contributing to Mn detoxification. We hope this review will provide a comprehensive understanding of the adaptive strategies of plants to Mn toxicity through gene regulation, which will aid in breeding crop varieties with Mn tolerance via genetic improvement approaches, enhancing the yield and quality of crops.
Manganese (Mn) toxicity is a major constraint limiting plant growth on acidic soils. Superior Mn tolerance in Stylosanthes spp. has been well documented, but its molecular mechanisms remain largely ...unknown. In this study, superior Mn tolerance in Stylosanthes guianensis was confirmed, as reflected by a high Mn toxicity threshold. Furthermore, genetic variation of Mn tolerance was evaluated using two S. guianensis genotypes, which revealed that the Fine-stem genotype had higher Mn tolerance than the TPRC2001-1 genotype, as exhibited through less reduction in dry weight under excess Mn, and accompanied by lower internal Mn concentrations. Interestingly, Mn-stimulated increases in malate concentrations and exudation rates were observed only in the Fine-stem genotype. Proteomic analysis of Fine-stem roots revealed that S. guianensis Malate Dehydrogenase1 (SgMDH1) accumulated in response to Mn toxicity. Western-blot and quantitative PCR analyses showed that Mn toxicity resulted in increased SgMDH1 accumulation only in Fine-stem roots, but not in TPRC2001-1. The function of SgMDH1-mediated malate synthesis was verified through in vitro biochemical analysis of SgMDH1 activities against oxaloacetate, as well as in vivo increased malate concentrations in yeast (Saccharomyces cerevisiae), soybean (Glycine max) hairy roots, and Arabidopsis (Arabidopsis thaliana) with SgMDH1 overexpression. Furthermore, SgMDH1 overexpression conferred Mn tolerance in Arabidopsis, which was accompanied by increased malate exudation and reduced plant Mn concentrations, suggesting that secreted malate could alleviate Mn toxicity in plants. Taken together, we conclude that the superior Mn tolerance of S. guianensis is achieved by coordination of internal and external Mn detoxification through malate synthesis and exudation, which is regulated by SgMDH1 at both transcription and protein levels.
Manganese (Mn), an essential element for plants, can be toxic when present in excess. Stylo (Stylosanthes) is a pioneer tropical legume with great potential for Mn tolerance, but its Mn tolerance ...mechanisms remain poorly understood.
In this study, variations in Mn tolerance were observed among nine stylo genotypes. Stylo genotype 'RY5' exhibited the highest Mn tolerance compared to the other tested genotypes, whereas 'TF2001' was a Mn-sensitive genotype. The mechanisms underlying the response of stylo to Mn toxicity were further investigated using these two genotypes with contrasting Mn tolerance. Results showed that stylo genotype RY5 exhibited Mn tolerance superior to that of genotype TF2001, showing lower reductions in leaf chlorophyll concentration, chlorophyll fluorescence parameters, photosynthetic indexes and plant dry weight under Mn toxicity. A label-free quantitative proteomic analysis was conducted to investigate the protein profiles in the leaves and roots of RY5 in response to Mn toxicity. A total of 356 differentially expressed proteins (DEPs) were identified, including 206 proteins from leaves and 150 proteins from roots, which consisted of 71 upregulated, 62 downregulated, 127 strongly induced and 96 completely suppressed proteins. These DEPs were mainly involved in defense response, photosynthesis, carbon fixation, metabolism, cell wall modulation and signaling. The qRT-PCR analysis verified that 10 out of 12 corresponding gene transcription patterns correlated with their encoding proteins after Mn exposure. Finally, a schematic was constructed to reveal insights into the molecular processes in the leaves and roots of stylo in response to Mn toxicity.
These findings suggest that stylo plants may cope with Mn toxicity by enhancing their defense response and phenylpropanoid pathways, adjusting photosynthesis and metabolic processes, and modulating protein synthesis and turnover. This study provides a platform for the future study of Mn tolerance mechanisms in stylo and may lead to a better understanding of the potential mechanisms underlying tropical legume adaptation to Mn toxicity.
Phosphorus (P) deficiency is one of the major constraints limiting plant growth, especially in acid soils. Stylosanthes (stylo) is a pioneer tropical legume with excellent adaptability to low P ...stress, but its underlying mechanisms remain largely unknown.
In this study, the physiological, molecular and metabolic changes in stylo responding to phosphate (Pi) starvation were investigated. Under low P condition, the growth of stylo root was enhanced, which was attributed to the up-regulation of expansin genes participating in root growth. Metabolic profiling analysis showed that a total of 256 metabolites with differential accumulations were identified in stylo roots response to P deficiency, which mainly included flavonoids, sugars, nucleotides, amino acids, phenylpropanoids and phenylamides. P deficiency led to significant reduction in the accumulation of phosphorylated metabolites (e.g., P-containing sugars, nucleotides and cholines), suggesting that internal P utilization was enhanced in stylo roots subjected to low P stress. However, flavonoid metabolites, such as kaempferol, daidzein and their glycoside derivatives, were increased in P-deficient stylo roots. Furthermore, the qRT-PCR analysis showed that a set of genes involved in flavonoids synthesis were found to be up-regulated by Pi starvation in stylo roots. In addition, the abundances of phenolic acids and phenylamides were significantly increased in stylo roots during P deficiency. The increased accumulation of the metabolites in stylo roots, such as flavonoids, phenolic acids and phenylamides, might facilitate P solubilization and cooperate with beneficial microorganisms in rhizosphere, and thus contributing to P acquisition and utilization in stylo.
These results suggest that stylo plants cope with P deficiency by modulating root morphology, scavenging internal Pi from phosphorylated metabolites and increasing accumulation of flavonoids, phenolic acids and phenylamides. This study provides valuable insights into the complex responses and adaptive mechanisms of stylo roots to P deficiency.
As a heavy metal, manganese (Mn) can be toxic to plants. Stylo (Stylosanthes) is an important tropical legume that exhibits tolerance to high levels of Mn. However, little is known about the adaptive ...responses of stylo to Mn toxicity. Thus, this study integrated both physiological and transcriptomic analyses of stylo subjected to Mn toxicity.
Results showed that excess Mn treatments increased malondialdehyde (MDA) levels in leaves of stylo, resulting in the reduction of leaf chlorophyll concentrations and plant dry weight. In contrast, the activities of enzymes, such as peroxidase (POD), phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO), were significantly increased in stylo leaves upon treatment with increasing Mn levels, particularly Mn levels greater than 400 μM. Transcriptome analysis revealed 2471 up-regulated and 1623 down-regulated genes in stylo leaves subjected to Mn toxicity. Among them, a set of excess Mn up-regulated genes, such as genes encoding PAL, cinnamyl-alcohol dehydrogenases (CADs), chalcone isomerase (CHI), chalcone synthase (CHS) and flavonol synthase (FLS), were enriched in secondary metabolic processes based on gene ontology (GO) analysis. Numerous genes associated with transcription factors (TFs), such as genes belonging to the C2H2 zinc finger transcription factor, WRKY and MYB families, were also regulated by Mn in stylo leaves. Furthermore, the C2H2 and MYB transcription factors were predicted to be involved in the transcriptional regulation of genes that participate in secondary metabolism in stylo during Mn exposure. Interestingly, the activation of secondary metabolism-related genes probably resulted in increased levels of secondary metabolites, including total phenols, flavonoids, tannins and anthocyanidins.
Taken together, this study reveals the roles of secondary metabolism in the adaptive responses of stylo to Mn toxicity, which is probably regulated by specific transcription factors.
Phosphorus (P) is an essential macronutrient element for plant growth, and deficiency of inorganic phosphate (Pi) limits plant growth and yield. Elephant grass (
) is an important fodder crop ...cultivated widely in tropical and subtropical areas throughout the world. However, the mechanisms underlying efficient P use in elephant grass under Pi deficiency remain poorly understood. In this study, the physiological and molecular responses of elephant grass leaves and roots to Pi deficiency were investigated. The results showed that dry weight, total P concentration, and P content decreased in Pi-deprived plants, but that acid phosphatase activity and P utilization efficiency (PUE) were higher than in Pi-sufficient plants. Regarding Pi starvation-responsive (PSR) genes, transcriptomics showed that 59 unigenes involved in Pi acquisition and transport (especially 18
and 27
unigenes) and 51
unigenes involved in phospholipids degradation or Pi-free lipids biosynthesis, as well as 47 core unigenes involved in the synthesis of phenylpropanoids and flavonoids, were significantly up-regulated by Pi deprivation in leaves or roots. Furthermore, 43 unigenes related to Pi-independent- or inorganic pyrophosphate (PPi)-dependent bypass reactions were markedly up-regulated in Pi-deficient leaves, especially five
and 15
unigenes. Consistent with PSR unigene expression changes, metabolomics revealed that Pi deficiency significantly increased metabolites of Pi-free lipids, phenylpropanoids, and flavonoids in leaves and roots, but decreased phospholipid metabolites. This study reveals the mechanisms underlying the responses to Pi starvation in elephant grass leaves and roots, which provides candidate unigenes involved in efficient P use and theoretical references for the development of P-efficient elephant grass varieties.
Stylosanthes
spp. (stylo) are annual or perennial legume forages that are widely grown as forage and cover crops in tropical and subtropical regions. However, the seed yield of stylo is very low due ...to serious seed shattering. In the present study, we found that, although seed shattering was common among the stylo accessions, the shattering rates were genetically different. Therefore, we first synthesized the morphological, histological characteristic, physiochemical, and transcriptome analyses to determine the seed shattering mechanism in stylo. In general, the stylo germplasm with shorter lobules and thicker stems had a lower seed shattering rate and a higher seed weight. The seed and seed stalk joint is the abscission zone in stylo. Multiplex histology and hydrolytic enzyme activity analysis showed that the tearing of the abscission zone occurs due to the intense enzymatic degradation of polygalacturonase and cellulase in the seed shattering-susceptible accession TF0275. cDNA libraries from the abscission zone tissues of TF0041 and TF0275 at 14, 21, and 28 days after flowering were constructed and sequenced. A total of 47,606 unigenes were annotated and 18,606 differentially expressed genes (DEGs) were detected, including 9,140 upregulated and 9,446 downregulated unigenes. Furthermore, the 26 candidate DEGs involved in lignin biosynthesis, cellulase synthesis, and plant hormone signal transduction were found at all three developmental stages. This study provides valuable insights for future mechanistic studies of seed shattering in stylo.
Stylosanthes (stylo) is a dominant leguminous forage in the tropics. Previous studies suggest that stylo has great potential for aluminium (Al) tolerance, but little is known about the underlying ...mechanism. A novel malic enzyme, SgME1, was identified from the Al‐tolerant genotype TPRC2001‐1 after 72 h Al exposure by two‐dimensional electrophoresis, and the encoding gene was cloned and characterized via heterologous expression in yeast, Arabidopsis thaliana and bean (Phaseolus vulgaris) hairy roots. Internal Al detoxification might be mainly responsible for the 72 h Al tolerance of TPRC2001‐1, as indicated by 5.8‐fold higher root malate concentrations and approximately two‐fold higher Al concentrations in roots and root symplasts of TPRC2001‐1 than those of the Al‐sensitive genotype Fine‐stem. An accompanying increase in malate secretion might also reduce a fraction of Al uptake in TPRC2001‐1. Gene and protein expression of SgME1 was only enhanced in TPRC2001‐1 after 72 h Al exposure. Overexpressing SgME1 enhanced malate synthesis and rescued yeast, A. thaliana and bean hairy roots from Al toxicity via increasing intracellular malate concentrations and/or accompanied malate exudation. These results provide strong evidence that superior Al tolerance of stylo is mainly conferred by Al‐enhanced malate synthesis, functionally controlled by SgME1.
Soybean (Glycine max) is a vital oil-producing crop. Augmenting oleic acid (OA) levels in soybean oil enhances its oxidative stability and health benefits, representing a key objective in soybean ...breeding. Pongamia (Pongamia pinnata), known for its abundant oil, OA, and flavonoid in the seeds, holds promise as a biofuel and medicinal plant. A comparative analysis of the lipid and flavonoid biosynthesis pathways in Pongamia and soybean seeds would facilitate the assessment of the potential value of Pongamia seeds and advance the genetic improvements of seed traits in both species. The study employed multi-omics analysis to systematically compare differences in metabolite accumulation and associated biosynthetic genes between Pongamia seeds and soybean seeds at the transcriptional, metabolic, and genomic levels. The results revealed that OA is the predominant free fatty acid in Pongamia seeds, being 8.3 times more abundant than in soybean seeds. Lipidomics unveiled a notably higher accumulation of triacylglycerols (TAGs) in Pongamia seeds compared to soybean seeds, with 23 TAG species containing OA. Subsequently, we identified orthologous groups (OGs) involved in lipid biosynthesis across 25 gene families in the genomes of Pongamia and soybean, and compared the expression levels of these OGs in the seeds of the two species. Among the OGs with expression levels in Pongamia seeds more than twice as high as in soybean seeds, we identified one fatty acyl-ACP thioesterase A (FATA) and two stearoyl-ACP desaturases (SADs), responsible for OA biosynthesis, along with two phospholipid:diacylglycerol acyltransferases (PDATs) and three acyl-CoA:diacylglycerol acyltransferases (DGATs), responsible for TAG biosynthesis. Furthermore, we observed a significantly higher content of the flavonoid formononetin in Pongamia seeds compared to soybean seeds, by over 2000-fold. This difference may be attributed to the tandem duplication expansions of 2,7,4ʹ-trihydroxyisoflavanone 4ʹ-O-methyltransferases (HI4ʹOMTs) in the Pongamia genome, which are responsible for the final step of formononetin biosynthesis, combined with their high expression levels in Pongamia seeds. This study extends beyond observations made in single-species research by offering novel insights into the molecular basis of differences in lipid and flavonoid biosynthetic pathways between Pongamia and soybean, from a cross-species comparative perspective.
As a pioneer tropical pasture legume, stylo (Stylosanthes guianensis) is well adapted to growth-limiting factors in acid soils. Considering the importance of stylo, there is a need to improve ...Agrobacterium-mediated genetic transformation to enable development of elite cultivars. In this study, S. guianensis cv. RY5 was used to systematically optimize Agrobacterium-mediated transformation based on its plant regeneration. Results showed that Murashige and Skoog (MS) medium containing 0.2 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) and 2 mg/L 6-benzylaminopurine (6-BA) was the optimal callus induction medium. MS medium supplemented with 2 mg/L 6-BA was suitable for shoot regeneration from cotyledon-derived calluses, and 0.5 mg/L indole-3-acetic acid (IAA) and 0.5 mg/L indole-3-butyric acid (IBA) applications were beneficial for rooting. The highest transformation efficiency (67%) was obtained at an Agrobacterium concentration of optical density = 0.6 combined with an infection time of 15 min and 3 days of co-cultivation. Furthermore, 200 mg/mL carbenicillin (Carb) and 0.6 mg/L Basta® supplements were effective in eliminating excess bacterial growth and selecting transgenic plants, respectively. Subsequent polymerase chain reaction (PCR) analysis confirmed that the β-glucuronidase (GUS) and BAR genes were successfully integrated into the stylo genome. Wider testing of this improved protocol as a means of enhancing genetic improvement and gene function analysis of stylo seems warranted.
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