A novel rice fragile culm 24 mutant encodes a UDP-glucose epimerase that affects cell wall properties and photosynthesis

Cell wall remodeling confers plant architecture with distinct wall structure in Nelumbo nucifera

Lotus (Nelumbo nucifera G.) is a perennial aquatic horticultural plant with diverse architectures. Distinct plant architecture (PA) has certain attractive and practical qualities, but its genetic morphogenesis in lotus remains elusive. In this study, we employ genome-wide association analysis (GWAS) for the seven traits of petiole length (PLL), leaf length (LL), leaf width (LW), peduncle length (PLF), flower diameter (FD), petal length (PeL), and petal width (PeW) in 301 lotus accessions. A total of 90 loci are identified to associate with these traits across 4 years of trials. Meanwhile, we perform RNA sequencing (RNA-seq) to analyze the differential expression of the gene (DEG) transcripts between large and small PA (LPA and SPA) of lotus stems (peduncles and petioles). As a result, eight key candidate genes are identified that are all primarily involved in plant cell wall remodeling significantly associated with PA traits by integrating the results of DEGs and GWAS. To verify this result, we compare the cell wall compositions and structures of LPA versus SPA in representative lotus germplasms. Intriguingly, compared with the SPA lotus, the LPA varieties have higher content of cellulose and hemicellulose, but less filling substrates of pectin and lignin. Additionally, we verified longer cellulose chains and higher cellulose crystallinity with less interference in LPA varieties. Taken together, our study illustrates how plant cell wall remodeling affects PA in lotus, shedding light on the genetic architecture of this significant ornamental trait and offering a priceless genetic resource for future genomic-enabled breeding.

Applications of the Yariv reagent in polysaccharide analysis and plant physiology from theory to practice

Arabinogalactan (AG), a biologically active substance found abundantly in plants, is of significant interest in plant physiology due to its unique physicochemical properties. Yariv reagent, widely utilized in AG-II related applications, forms insoluble precipitates when bound to AG-II. This paper provides a comprehensive overview of the synthesis methods, physicochemical properties, and various dissociation methods of the Yariv reagent to enhance its utility in AG-II studies. Furthermore, the review explores the binding mechanisms and applications of the Yariv reagent, highlighting the advancements in studying the Yariv-AG complex in plant physiology. The aim of this review is to inspire new research ideas and foster novel applications of the Yariv reagent from synthesis to implementation.

Strong culm: a crucial trait for developing next-generation climate-resilient rice lines

Lodging, a phenomenon characterized by the bending or breaking of rice plants, poses substantial constraints on productivity, particularly during the harvesting phase in regions susceptible to strong winds. The rice strong culm trait is influenced by the intricate interplay of genetic, physiological, epigenetic, and environmental factors. Stem architecture, encompassing morphological and anatomical attributes, alongside the composition of both structural and non-structural carbohydrates, emerges as a critical determinant of lodging resistance. The adaptive response of the rice culm to various biotic and abiotic environmental factors further modulates the propensity for lodging. Advancements in next-generation sequencing technologies have expedited the genetic dissection of lodging resistance, enabling the identification of pertinent genes, quantitative trait loci, and novel alleles. Concurrently, contemporary breeding strategies, ranging from biparental approaches to more sophisticated methods such as multi-parent-based breeding, gene pyramiding, genomic selection, genome-wide association studies, and haplotype-based breeding, offer perspectives on the genetic underpinnings of culm strength. This review comprehensively delves into physiological attributes, culm histology, epigenetic determinants, and gene expression profiles associated with lodging resistance, with a specialized focus on leveraging next-generation sequencing for candidate gene discovery.

Side chain of confined xylan affects cellulose integrity leading to bending stem with reduced mechanical strength in ornamental plants

The stem support for fresh-cut flowers exerts a profound influence on the display of their blossoms. During vase insertion, bending stems significantly affect the ornamental value, but much remains unclear about the underlying reasons. In this study, six pairs of ornamental plants were screened for the contrast of bending and straight stems. The bending stems have weakened mechanical force and biomass recalcitrance compared with the straight ones. Meanwhile, cells in the bending stems became more loosely packed, along with a decrease in cell wall thickness and cellulose levels. Furthermore, wall properties characterizations show bending stems have decreased lignocellulosic CrI and cellulose DP, and enhanced the branching ratio of hemicellulose which is trapped in the cellulose. Given the distinct cell wall factors in different species, all data are grouped in standardized to eliminate the variations among plant species. The principal composition analysis and correlation analysis of the processed dataset strongly suggest that cellulose association factors determine the stem mechanical force and recalcitrance. Based on our results, we propose a model for how branches of confined hemicellulose interacted with cellulose to modulate stem strength support for the straight or bending phenotype in cut flowers.

OsUGE2 Regulates Plant Growth through Affecting ROS Homeostasis and Iron Level in Rice

BACKGROUND

The growth and development of rice (Oryza sativa L.) are affected by multiple factors, such as ROS homeostasis and utilization of iron. Here, we demonstrate that OsUGE2, a gene encoding a UDP-glucose 4-epimerase, controls growth and development by regulating reactive oxygen species (ROS) and iron (Fe) level in rice. Knockout of this gene resulted in impaired growth, such as dwarf phenotype, weakened root growth and pale yellow leaves. Biochemical analysis showed that loss of function of OsUGE2 significantly altered the proportion and content of UDP-Glucose (UDP-Glc) and UDP-Galactose (UDP-Gal). Cellular observation indicates that the impaired growth may result from decreased cell length. More importantly, RNA-sequencing analysis showed that knockout of OsUGE2 significantly influenced the expression of genes related to oxidoreductase process and iron ion homeostasis. Consistently, the content of ROS and Fe are significantly decreased in OsUGE2 knockout mutant. Furthermore, knockout mutants of OsUGE2 are insensitive to both Fe deficiency and hydrogen peroxide (H2O2) treatment, which further confirmed that OsUGE2 control rice growth possibly through Fe and H2O2 signal. Collectively, these results reveal a new pathway that OsUGE2 could affect growth and development via influencing ROS homeostasis and Fe level in rice.

Reciprocal regulation of cellulose and lignin biosynthesis by the transcription factor OsTCP19

This article comments on:

Lv S, Lin Z, Shen J, Luo L, Xu Q, Li L, Gui J. 2024. OsTCP19 coordinates inhibition of lignin biosynthesis and promotion of cellulose biosynthesis to modify lodging resistance in rice. Journal of Experimental Botany 75, 123–136.

BOTRYOID POLLEN 1 regulates ROS-triggered PCD and pollen wall development by controlling UDP-sugar homeostasis in rice

Uridine diphosphate (UDP)-sugars are important metabolites involved in the biosynthesis of polysaccharides and may be important signaling molecules. UDP-glucose 4-epimerase (UGE) catalyzes the interconversion between UDP-Glc and UDP-Gal, whose biological function in rice (Oryza sativa) fertility is poorly understood. Here, we identify and characterize the botryoid pollen 1 (bp1) mutant and show that BP1 encodes a UGE that regulates UDP-sugar homeostasis, thereby controlling the development of rice anthers. The loss of BP1 function led to massive accumulation of UDP-Glc and imbalance of other UDP-sugars. We determined that the higher levels of UDP-Glc and its derivatives in bp1 may induce the expression of NADPH oxidase genes, resulting in a premature accumulation of reactive oxygen species (ROS), thereby advancing programmed cell death (PCD) of anther walls but delaying the end of tapetal degradation. The accumulation of UDP-Glc as metabolites resulted in an abnormal degradation of callose, producing an adhesive microspore. Furthermore, the UDP-sugar metabolism pathway is not only involved in the formation of intine but also in the formation of the initial framework for extine. Our results reveal how UDP-sugars regulate anther development and provide new clues for cellular ROS accumulation and PCD triggered by UDP-Glc as a signaling molecule.

UDP-glucose epimerase 1, moonlighting as a transcriptional activator, is essential for tapetum degradation and male fertility in rice

Multiple enzymes perform moonlighting functions distinct from their main roles. UDP-glucose epimerases (UGEs), a subclass of isomerases, catalyze the interconversion of UDP-glucose (UDP-Glc) and UDP-galactose (UDP-Gal). We identified a rice male-sterile mutant, osuge1, with delayed tapetum degradation and abortive pollen. The mutant osuge1 protein lacked UDP-glucose epimerase activity, resulting in higher UDP-Gal content and lower UDP-Glc levels in the osuge1 mutant compared with the wild type. Interestingly, we discovered that OsUGE1 participates in the TIP2/bHLH142-TDR-EAT1/DTD transcriptional regulatory cascade involved in tapetum degradation, in which TIP2 and TDR regulate the expression of OsUGE1 while OsUGE1 regulates the expression of EAT1. In addition, we found that OsUGE1 regulates the expression of its own gene by directly binding to an E-box element in the OsUGE1 promoter. Collectively, our results indicate that OsUGE1 not only functions as a UDP-glucose epimerase but also moonlights as a transcriptional activator to promote tapetum degradation, revealing a novel regulatory mechanism of rice reproductive development.

OsUGE1 is directly targeted by OsGRF6 to regulate root hair length in rice

KEY MESSAGE

Root hairs are required for water and nutrient acquisition in plants. Here, we report a novel mechanism that OsUGE1 is negatively controlled by OsGRF6 to regulate root hair elongation in rice. Root hairs are tubular outgrowths generated by the root epidermal cells. They effectively enlarge the soil-root contact area and play essential roles for nutrient and water absorption. Here, in this study, we demonstrated that the Oryza sativa UDP-glucose 4-epimerase 1-like (OsUGE1) negatively regulated root hair elongation and was directly targeted by Oryza sativa growth regulating factor 6 (OsGRF6). Knockout mutants of OsUGE1 using CRISPR-Cas9 technology showed longer root hairs than those of wild type. In contrast, overexpression lines of OsUGE1 displayed shorter root hair compared with those of wild type. GUS staining showed that it could specifically express in root hair. Subcellular localization analysis indicates that OsUGE1 is located in endoplasmic reticulum, nucleus and plasma membrane. More importantly, ChIP-qPCR, Yeast-one-hybrid and BiFC experiments revealed that OsGRF6 could bind to the promoter of OsUGE1. Furthermore, knockout mutants of OsGRF6 showed shorter root hair than those of wild type, and OsGRF6 dominantly expressed in root. In addition, the expression level of OsUGE1 is significantly downregulated in Osgrf6 mutant. Taken together, our study reveals a novel pathway that OsUGE1 is negatively controlled by OsGRF6 to regulate root hair elongation in rice.

A large-scale forward genetic screen for maize mutants with altered lignocellulosic properties

The development of efficient pipelines for the bioconversion of grass lignocellulosic feedstocks is challenging due to the limited understanding of the molecular mechanisms controlling the synthesis, deposition, and degradation of the varying polymers unique to grass cell walls. Here, we describe a large-scale forward genetic approach resulting in the identification of a collection of chemically mutagenized maize mutants with diverse alterations in their cell wall attributes such as crystalline cellulose content or hemicellulose composition. Saccharification yield, i.e. the amount of lignocellulosic glucose (Glc) released by means of enzymatic hydrolysis, is increased in two of the mutants and decreased in the remaining six. These mutants, termed candy-leaf (cal), show no obvious plant growth or developmental defects despite associated differences in their lignocellulosic composition. The identified cal mutants are a valuable tool not only to understand recalcitrance of grass lignocellulosics to enzymatic deconstruction but also to decipher grass-specific aspects of cell wall biology once the genetic basis, i.e. the location of the mutation, has been identified.

Single-molecular insights into the breakpoint of cellulose nanofibers assembly during saccharification

Plant cellulose microfibrils are increasingly employed to produce functional nanofibers and nanocrystals for biomaterials, but their catalytic formation and conversion mechanisms remain elusive. Here, we characterize length-reduced cellulose nanofibers assembly in situ accounting for the high density of amorphous cellulose regions in the natural rice fragile culm 16 (Osfc16) mutant defective in cellulose biosynthesis using both classic and advanced atomic force microscopy (AFM) techniques equipped with a single-molecular recognition system. By employing individual types of cellulases, we observe efficient enzymatic catalysis modes in the mutant, due to amorphous and inner-broken cellulose chains elevated as breakpoints for initiating and completing cellulose hydrolyses into higher-yield fermentable sugars. Furthermore, effective chemical catalysis mode is examined in vitro for cellulose nanofibers conversion into nanocrystals with reduced dimensions. Our study addresses how plant cellulose substrates are digestible and convertible, revealing a strategy for precise engineering of cellulose substrates toward cost-effective biofuels and high-quality bioproducts.

Intermittent ultrasound retains cellulases unlock for enhanced cellulosic ethanol with high-porosity biochar for dye adsorption using desirable rice mutant straw

In this study, optimal ultrasound pretreatment was performed with recalcitrance-reduced rice mutant straw to effectively extract lignin and hemicellulose for improved cellulose accessibility. Intermittent ultrasound-assistant enzymatic hydrolyses were followed to maintain more cellulases unlock and less cellulose surface block with lignin for raised hexose yield at 81 % (% cellulose) and bioethanol concentration at 9.9 g/L, which was higher than those of other mechanical pretreatments as previously conducted. Using all enzyme-undigestible lignocellulose residues, this work generated the biochar with the highest porosity (S_BET at 2971 m²/g) among all biomass-based biochar obtained from previous studies. Furthermore, the biochar were respectively examined with high adsorption capacity for Congo red and methylene blue at 7946 mg/g and 861 mg/g. Therefore, this study has demonstrated a green-like process technology for high-yield bioethanol and high-porosity biochar with full biomass utilization by integrating optimal ultrasound pretreatment with intermittent ultrasound-assistant enzymatic hydrolyses of recalcitrance-reduced lignocellulose in crop straws.

Pre-harvest Nitrogen Limitation and Continuous Lighting Improve the Quality and Flavor of Lettuce (Lactuca sativa L.) under Hydroponic Conditions in Greenhouse

Short-term nitrogen limitation and continuous lighting (red/blue = 3:1) were applied individually and in combination to butterhead and red oak leaf lettuce for 1, 2, or 3 days before harvest to assess their effects on improving the nutritional value and sweet taste and reducing nitrate content and bitterness of lettuce. The results suggested that a 3-day nitrogen limitation combined with continuous lighting reduced the lettuce content of nitrate and sesquiterpene lactones and improved the quantities of soluble sugar, soluble protein, anthocyanins, and phenolic compounds without reducing the fresh weight of lettuce. In addition, in vitro simulated digestion results suggested that the 3-day nitrogen limitation combined with continuous lighting significantly improved the sweetness and reduced the bitterness of lettuce compared to the control. In conclusion, nitrogen limitation combined with continuous lighting for 3 days before harvest effectively enhanced the quality and taste of lettuce, showing great potential for its use in hydroponic lettuce production.

Combined physiological and metabolomic analysis reveals the effects of different biostimulants on maize production and reproduction

Plant biostimulants (PBs) are a potential strategy to improve crop growth and grain quality. In the present study, 100 mg/L trehalose, chitosan, humic acid and gamma-aminobutyric acid treatments were applied to analyze the effects of maize production and reproductive characteristics. The contents of nitrogen, phosphorus and potassium and grain quality were significantly affected by the PBs, but not yield. The seed germination rate of all PB treatments was significantly reduced, but the drought resistance of progeny seedlings was significantly improved, with humic acid having the strongest effect. Liquid chromatography mass spectrometry analysis indicated that the disruption of the tricarboxylic acid cycle, probably due to the blockage of intermediate anabolism, reduced the supply of energy and nutrients in the early stages of germination, thus inhibiting seed germination, while the increased resistance of the offspring seedlings may be due to the up-regulation of the synthesis of unsaturated fatty acids and alkaloids by humic acid treatment. This study revealed the similarity and heterogeneity of the effects of different PBs on nutrient accumulation, yield characteristics and grain quality of maize, providing guidance for the application of PBs in intensive and sustainable agricultural production.

CEF3 is involved in membrane trafficking and essential for secondary cell wall biosynthesis and its mutation enhanced biomass enzymatic saccharification in rice

Background

As one of the most important staple food crops, rice produces large of agronomic biomass residues that contain lots of secondary cell walls (SCWs). Membrane trafficking plays key roles in SCWs biosynthesis, but information association membrane trafficking and SCWs formation in plants is limited.

Results

In this study, we report the function characterization of a rice mutant, culm easily fragile 3 (cef3), that exhibits growth retardation and fragile culm phenotype with significantly altered cell wall composition and reduced secondary wall thickness. Map-based cloning revealed that CEF3 encodes a homologous protein of Arabidopsis STOMATAL CYTOKINESIS DEFECTIVE2 (SCD2). The saccharification assays revealed that CEF3 mutation can improve biomass enzymatic saccharification. Expression pattern analysis indicated that CEF3 is ubiquitously expressed in many organs at different developmental stages. Subcellular localization revealed that CEF3 is a Golgi-localized protein. The FM4-64 uptake assay revealed CEF3 is involved in endocytosis. Furthermore, mutation of CEF3 not only affected cellulose synthesis-related genes expression, but also altered the abundance of cellulose synthase catalytic subunit 9 (OsCESA9) in the PM and in the endomembrane systems.

Conclusions

This study has demonstrated that CEF3 participates in the membrane trafficking that is essential for normal cellulose and other polysaccharides biosynthesis of the secondary cell wall, thereby manipulation of CEF3 could alter cellulose content and enhance biomass enzymatic saccharification in rice plants. Therefore, the study of the function of CEF3 can provide a strategy for genetic modification of SCWs in bioenergy crops.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02205-y.

Disruption of OsPHD1, Encoding a UDP-Glucose Epimerase, Causes JA Accumulation and Enhanced Bacterial Blight Resistance in Rice

Lesion mimic mutants (LMMs) have been widely used in experiments in recent years for studying plant physiological mechanisms underlying programmed cell death (PCD) and defense responses. Here, we identified a lesion mimic mutant, lm212-1, which cloned the causal gene by a map-based cloning strategy, and verified this by complementation. The causal gene, OsPHD1, encodes a UDP-glucose epimerase (UGE), and the OsPHD1 was located in the chloroplast. OsPHD1 was constitutively expressed in all organs, with higher expression in leaves and other green tissues. lm212-1 exhibited decreased chlorophyll content, and the chloroplast structure was destroyed. Histochemistry results indicated that H₂O₂ is highly accumulated and cell death is occurred around the lesions in lm212-1. Compared to the wild type, expression levels of defense-related genes were up-regulated, and resistance to bacterial pathogens Xanthomonas oryzae pv. oryzae (Xoo) was enhanced, indicating that the defense response was activated in lm212-1, ROS production was induced by flg22, and chitin treatment also showed the same result. Jasmonic acid (JA) and methyl jasmonate (MeJA) increased, and the JA signaling pathways appeared to be disordered in lm212-1. Additionally, the overexpression lines showed the same phenotype as the wild type. Overall, our findings demonstrate that OsPHD1 is involved in the regulation of PCD and defense response in rice.

Down-regulation of OsMYB103L distinctively alters beta-1,4-glucan polymerization and cellulose microfibers assembly for enhanced biomass enzymatic saccharification in rice

BACKGROUND

As a major component of plant cell walls, cellulose provides the most abundant biomass resource convertible for biofuels. Since cellulose crystallinity and polymerization have been characterized as two major features accounting for lignocellulose recalcitrance against biomass enzymatic saccharification, genetic engineering of cellulose biosynthesis is increasingly considered as a promising solution in bioenergy crops. Although several transcription factors have been identified to regulate cellulose biosynthesis and plant cell wall formation, much remains unknown about its potential roles for genetic improvement of lignocellulose recalcitrance.

RESULTS

In this study, we identified a novel rice mutant (Osfc9/myb103) encoded a R2R3-MYB transcription factor, and meanwhile generated OsMYB103L-RNAi-silenced transgenic lines. We determined significantly reduced cellulose levels with other major wall polymers (hemicellulose, lignin) slightly altered in mature rice straws of the myb103 mutant and RNAi line, compared to their wild type (NPB). Notably, the rice mutant and RNAi line were of significantly reduced cellulose features (crystalline index/CrI, degree of polymerization/DP) and distinct cellulose nanofibers assembly. These alterations consequently improved lignocellulose recalcitrance for significantly enhanced biomass enzymatic saccharification by 10-28% at p < 0.01 levels (n = 3) after liquid hot water and chemical (1% H₂SO₄, 1% NaOH) pretreatments with mature rice straws. In addition, integrated RNA sequencing with DNA affinity purification sequencing (DAP-seq) analyses revealed that the OsMYB103L might specifically mediate cellulose biosynthesis and deposition by regulating OsCesAs and other genes associated with microfibril assembly.

CONCLUSIONS

This study has demonstrated that down-regulation of OsMYB103L could specifically improve cellulose features and cellulose nanofibers assembly to significantly enhance biomass enzymatic saccharification under green-like and mild chemical pretreatments in rice. It has not only indicated a powerful strategy for genetic modification of plant cell walls in bioenergy crops, but also provided insights into transcriptional regulation of cellulose biosynthesis in plants.

Adjustments in photosynthesis and leaf water relations are related to changes in cell wall composition in Hordeum vulgare and Triticum aestivum subjected to water deficit stress

In the current climate change scenario, understanding crops' physiological performance under water shortage is crucial to overcome drought periods. Although the implication of leaf water relations maintaining leaf turgor and stomatal functioning under water deprivation has been suggested, the relationships between photosynthesis and osmotic and elastic adjustments remain misunderstood. Similarly, only few studies in dicotyledonous analysed how changes in cell wall composition affected photosynthesis and leaf water relations under drought. To induce modifications in photosynthesis, leaf water relations and cell wall composition, Hordeum vulgare and Triticum aestivum were subjected to different water regimes: control (CL, full irrigation), moderate and severe water deficit stress (Mod WS and Sev WS, respectively). Water shortage decreased photosynthesis mainly due to stomatal conductance (g_s) declines, being accompanied by reduced osmotic potential at full turgor (π_o) and increased bulk modulus of elasticity (ε). Whereas both species enhanced pectins when intensifying water deprivation, species-dependent adjustments occurred for cellulose and hemicelluloses. From these results, we showed that π_o and ε influenced photosynthesis, particularly, g_s. Furthermore, the (Cellulose+Hemicelluloses)/Pectins ratio determined ε and mesophyll conductance (g_m) in grasses, presenting the lowest pectins content within angiosperms. Thus, we highlight the relevance of cell wall composition regulating grasses physiology during drought acclimation.

Genomic divergence during feralization reveals both conserved and distinct mechanisms of parallel weediness evolution

Agricultural weeds are the most important biotic constraints to global crop production, and chief among these is weedy rice. Despite increasing yield losses from weedy rice in recent years worldwide, the genetic basis of weediness evolution remains unclear. Using whole-genome sequence analyses, we examined the origins and adaptation of Japanese weedy rice. We find evidence for a weed origin from tropical japonica crop ancestry, which has not previously been documented in surveys of weedy rice worldwide. We further show that adaptation occurs largely through different genetic mechanisms between independently-evolved temperate japonica- and tropical japonica-derived strains; most genomic signatures of positive selection are unique within weed types. In addition, some weedy rice strains have evolved through hybridization between weedy and cultivated rice with adaptive introgression from the crop. Surprisingly, introgression from cultivated rice confers not only crop-like adaptive traits (such as shorter plant height, facilitating crop mimicry) but also weedy-like traits (such as seed dormancy). These findings reveal how hybridization with cultivated rice can promote persistence and proliferation of weedy rice.

Reduced photosynthesis in Arabidopsis thaliana atpme17.2 and atpae11.1 mutants is associated to altered cell wall composition

The cell wall is a complex and dynamic structure that determines plants' performance by constant remodeling of its compounds. Although cellulose is its major load-bearing component, pectins are crucial to determine wall characteristics. Changes in pectin physicochemical properties, due to pectin remodeling enzymes (PRE), induce the rearrangement of cell wall compounds, thus, modifying wall architecture. In this work, we tested for the first time how cell wall dynamics affect photosynthetic properties in Arabidopsis thaliana pectin methylesterase atpme17.2 and pectin acetylesterase atpae11.1 mutants in comparison to wild-type Col-0. Our results showed maintained PRE activities comparing mutants with wild-type and no significant differences in cellulose, but cell wall non-cellulosic neutral sugars contents changed. Particularly, the amount of galacturonic acid (GalA) - which represents to some extent the pectin cell wall proportion - was reduced in the two mutants. Additionally, physiological characterization revealed that mutants presented a decreased net CO₂ assimilation (A_N ) because of reductions in both stomatal (g_s ) and mesophyll conductances (g_m ). Thus, our results suggest that atpme17.2 and atpae11.1 cell wall modifications due to genetic alterations could play a significant role in determining photosynthesis.

Cell wall thickness and composition are involved in photosynthetic limitation

The key role of cell walls in setting mesophyll conductance to CO2 (gm) and, consequently, photosynthesis is reviewed. First, the theoretical properties of cell walls that can affect gm are presented. Then, we focus on cell wall thickness (Tcw) reviewing empirical evidence showing that Tcw varies strongly among species and phylogenetic groups in a way that correlates with gm and photosynthesis; that is, the thicker the mesophyll cell walls, the lower the gm and photosynthesis. Potential interplays of gm, Tcw, dehydration tolerance, and hydraulic properties of leaves are also discussed. Dynamic variations of Tcw in response to the environment and their implications in the regulation of photosynthesis are discussed, and recent evidence suggesting an influence of cell wall composition on gm is presented. We then propose a hypothetical mechanism for the influence of cell walls on photosynthesis, combining the effects of thickness and composition, particularly pectins. Finally, we discuss the prospects for using biotechnology for enhancing photosynthesis by altering cell wall-related genes.

Identification and fine mapping of a recessive gene controlling zebra leaf phenotype in maize

Leaf color mutant is an important resource for studying chlorophyll biosynthesis and chloroplast development in maize. Here, a novel mutant zebra crossband 9 (zb9) with transverse green-/yellow-striped leaves appeared from ten-leaf stage until senescence was identified from mutant population derived from the maize inbred line RP125. The yellow section of the zb9 mutant displays a reduction of chlorophyll and carotenoid contents, as well as impaired chloroplast structure. Genetic analysis showed that the zb9 mutant phenotype was caused by a single recessive gene. Map-based cloning demonstrated that the zb9 locus was delimited into a 648 kb region on chromosome 1 covering thirteen open reading frames (ORFs). Among them, a point mutation (G to A) in exon 2 of the gene Zm00001d029151, named Zmzb9, was identified based on sequencing analysis. The causal gene Zmzb9 encodes UDP-glucose-4-epimerase 4 (UGE4), a key enzyme involved in chloroplast development and was considered as the only candidate gene controlling the mutant phenotype. Expression patterns indicated that the causal gene was abundantly expressed in the leaves and sheaths, as well as significantly downregulated in the mutant compared to that in the wild type. Subcellular localization showed that ZmZB9 was localized in chloroplasts and implied the putative gene involved in chloroplast development. Taken together, we propose that the causal gene Zmzb9 tightly associated with the zebra leaf phenotype, and the obtained gene here will help to uncover the regulatory mechanism of pigment biosynthesis and chloroplast development in maize.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01202-7.

Biosynthesis and Transport of Nucleotide Sugars for Plant Hemicellulose

Hemicellulose is entangled with cellulose through hydrogen bonds and meanwhile acts as a bridge for the deposition of lignin monomer in the secondary wall. Therefore, hemicellulose plays a vital role in the utilization of cell wall biomass. Many advances in hemicellulose research have recently been made, and a large number of genes and their functions have been identified and verified. However, due to the diversity and complexity of hemicellulose, the biosynthesis and regulatory mechanisms are yet unknown. In this review, we summarized the types of plant hemicellulose, hemicellulose-specific nucleotide sugar substrates, key transporters, and biosynthesis pathways. This review will contribute to a better understanding of substrate-level regulation of hemicellulose synthesis.