Pectin Methylesterase Gene Research Articles

Exogenous proline regulates pectin demethylation by rescuing pectin methylesterase functioning of cell wall from Cr(VI) toxicity in rice plants

BackgroundPlants are equipped with several sophisticated mechanisms to deal with heavy metals (HMs) toxicity. Cell walls, which are rich in pectin, are important in the sequestration and compartmentalization of HMs. Pectin demethylation is carried out by pectin methylesterase (PME), which is a crucial activity in cell walls for the adsorption of HMs. This study focused on the factors that contribute to chromium (Cr) adsorption in rice plants exposed to Cr(VI) treatments without proline (Pro) “Cr(VI)” and with Pro “Pro + Cr(VI)” application.ResultsThe results exhibited that when rice plants were treated with Cr(VI), their PME activity decreased, because Cr(VI) was bound to certain isoforms of PME and prevented the demethylation of pectin. The application of Pro increased PME activity by promoting the transcription of several PME-related genes. These genes were recognized on the basis of their similarity with PME genes in Arabidopsis. Gene expression variation factors (GEVFs) between the “Cr(VI)” and “Pro + Cr(VI)” treatments revealed that OsPME7 and OsPME9 have the highest positive GEVF values than other OsPME genes of rice. In addition, Pro application increased pectin content significantly in rice plants exposed to Cr(VI) stress. Proline application also leads to an increased concentration of Cr in rice roots compared with “Cr(VI)” treatments alone.ConclusionsThese findings suggest that Pro increased Cr(VI) adsorption in cell walls of rice plants by enhancing the PME activity and pectin content when exposed to “Cr(VI)” treatments, mainly regulated by OsPME7 and OsPME9.Graphical

Genome-wide identification of walnut (Juglans regia) PME gene family members and expression analysis during infection with Cryptosphaeria pullmanensis pathogens

Walnuts exhibit a higher resistance to diseases, though they are not completely immune. This study focuses on the Pectin methylesterase (PME) gene family to investigate whether it is involved in disease resistance in walnuts. These 21 genes are distributed across 12 chromosomes, with four pairs demonstrating homology. Variations in conserved motifs and gene structures suggest diverse functions within the gene family. Phylogenetic and collinear gene pairs of the PME family indicate that the gene family has evolved in a relatively stable way. The cis-acting elements and gene ontology enrichment of these genes, underscores their potential role in bolstering walnuts' defense mechanisms. Transcriptomic analyses were conducted under conditions of Cryptosphaeria pullmanensis infestation and verified by RT-qPCR. The results showed that certain JrPME family genes were activated in response, leading to the hypothesis that some members may confer resistance to the disease.

Phosphorus deficiency-induced cell wall pectin demethylesterification enhances cadmium accumulation in roots of Salix caprea

Regions affected by heavy metal contamination frequently encounter phosphorus (P) deficiency. Numerous studies highlight crucial role of P in facilitating cadmium (Cd) accumulation in woody plants. However, the regulatory mechanism by which P affects Cd accumulation in roots remains ambiguous. This study aims to investigate the effects of phosphorus (P) deficiency on Cd accumulation, Cd subcellular distribution, and cell wall components in the roots of Salix caprea under Cd stress. The results revealed that under P deficiency conditions, there was a 35.4% elevation in Cd content in roots, coupled with a 60.1% reduction in Cd content in shoots, compared to the P sufficiency conditions. Under deficient P conditions, the predominant response of roots to Cd exposure was the increased sequestration of Cd in root cell walls. The sequestration of Cd in root cell walls increased from 37.1% under sufficient P conditions to 66.7% under P deficiency, with pectin identified as the primary Cd binding site under both P conditions. Among cell wall components, P deficiency led to a significant 31.7% increase in Cd content within pectin compared to P sufficiency conditions, but did not change the pectin content. Notably, P deficiency significantly increased pectin methylesterase (PME) activity by regulating the expression of PME and PMEI genes, leading to a 10.4% reduction in the degree of pectin methylesterification. This may elucidate the absence of significant changes in pectin content under P deficiency conditions and the concurrent increase in Cd accumulation in pectin. Fourier transform infrared spectroscopy (FTIR) results indicated an increase in carboxyl groups in the root cell walls under P deficiency compared to sufficient P treatment. The results provide deep insights into the mechanisms of higher Cd accumulation in root mediated by P deficiency.

Epigenetic modification of a pectin methylesterase gene activates apoplastic iron reutilization in tomato roots.

Iron (Fe) distribution and reutilization are crucial for maintaining Fe homeostasis in plants. Here, we demonstrate that the tomato (Solanum lycopersicum) Colorless nonripening (Cnr) epimutant exhibits increased Fe retention in cell wall pectin due to an increase in pectin methylesterase (PME) activity. This ultimately leads to Fe deficiency responses even under Fe-sufficient conditions when compared to the wild type (WT). Whole-genome bisulfite sequencing revealed that modifications to cell wall-related genes, especially CG hypermethylation in the intron region of PECTIN METHYLESTERASE53 (SlPME53), are involved in the Cnr response to Fe deficiency. When this intron hypermethylation of SlPME53 was artificially induced in WT, we found that elevated SlPME53 expression was accompanied by increased PME activity and increased pectin-Fe retention. The manipulation of SlPME53, either through overexpression in WT or knockdown in Cnr, influenced levels of pectin methylesterification and accumulation of apoplast Fe in roots. Moreover, CG hypermethylation mediated by METHYLTRANSFERASE1 (SlMET1) increased SlPME53 transcript abundance, resulting in greater PME activity and higher Fe retention in cell wall pectin. Therefore, we conclude that the Cnr mutation epigenetically modulates SlPME53 expression by SlMET1-mediated CG hypermethylation, and thus the capacity of the apoplastic Fe pool, creating opportunities for genetic improvement of crop mineral nutrition.

Genome-wide analysis of the PME gene family reveals its role in suppressing fruit lignification in pear

In pears, the presence of stone cells adversely affects fruit quality. Pectin methylesterase (PME) plays various roles in plant biology, including lignin biosynthesis. However, only a limited fraction has been functionally characterized, and the distribution and function of PME in many Rosaceae trees remain unexplored. In this study, we identified 396 putative PME family candidate genes, with 81 in Pyrus bretschneideri, 92 in Malus domestica, 62 in Fragaria vesca, 65 in Prunus mume, 15 in Pyrus communis, and 81 in Pyrus pyrifolia. Leveraging insights from model plants, we categorized PME family genes into four groups. Additionally, the evolution of the PME gene family was shaped by various gene duplication events, primarily dispersed duplication, influenced by purifying selection. A specific gene, Pbr031522.1, designated PbPME35, emerged as a candidate associated with lignin biosynthesis in pear fruits, supported by RNA-seq data. The role of PbPME35 in repressing lignification was validated through its overexpression in pear callus and Arabidopsis. Overall, our findings highlight the ability of PbPME35 to reduce lignin content in pear fruit by downregulating the expression levels of lignin biosynthesis genes. These findings provide new insights into the characteristics of PME genes and their role in regulating lignification in pear fruits.

Waterlogging restricted cotton fiber elongation by reducing osmolyte accumulation and cell wall biosynthesis

Waterlogging severely threatens the formation of cotton fiber quality, especially the length. However, the underlying mechanism is still incompletely understood. Here, the experiment (control: soil relative water content at (75 ± 5)%; treatment: waterlogging for 6 days) was conducted during the flowering and boll forming stage using two upland cotton cultivars (Dexiamian 1 and Yuzaomian 9110) to investigate the effects of waterlogging on fiber development from both transcriptomic and physiological levels. The transcriptome analysis of 10 days post anthesis cotton fiber showed that waterlogging significantly regulated the expression of genes associated with fiber elongation events including osmotic solutes accumulation, fiber cell wall biosynthesis, and cell wall remodeling and loosening. Waterlogging decreased the sucrose input into cotton fiber, resulting in reduced sucrose and hexose contents. Under waterlogging, the accumulation of malate and K+ in both cultivars was reduced by decreasing phosphoenolpyruvate carboxylase (PEPC) activity and potassium transporter genes (GhPOT) expression, respectively. Thus, the total concentration of osmolytes was reduced, which dampened cotton fiber elongation. Due to reduced sucrose synthase activity and uridine diphosphate glucose content, the cellulose biosynthesis was limited, leading to decreased fiber cell wall accumulation, which was adverse to fiber elongation. Besides, genes responsible for cell wall remodeling and loosening, including xyloglucan endotransglucosylase/hydrolase genes (GhXTH), α-expansin genes (GhEXPA), and pectin methylesterase genes (GhPME) were also responsive to waterlogging, but in different ways between cultivars. Overall, the shortened cotton fiber could be attributed to reduced osmolytes accumulation and cell wall biosynthesis, whilst the effects of waterlogging on cotton fiber cell wall loosening require further exploration.

Genome-wide survey and evolutionary history of the pectin methylesterase (PME) gene family in the Dothideomycetes class of fungi

Once deposited in the plant cell wall, pectin undergoes demethylesterification by endogenous pectin methylesterases (PMEs), which play various roles in growth and development, including defense against pathogen attacks. Pathogen PMEs can alter pectin's methylesterification pattern, increasing its susceptibility to degradation by other fungal pectinases and thus playing a critical role as virulence factors during early infection stages. To investigate the evolutionary history of PMEs in the Dothideomycetes class of fungi, we obtained genomic data from 15 orders (79 species) and added genomic data from 61 isolates of Corynespora cassiicola. Our analyses involved maximum likelihood phylogenies, gene genealogies, and selection analyses. Additionally, we measured PME gene expression levels of C. cassiicola using soybean as a host through RT-qPCR assays. We recovered 145 putative effector PMEs and 57 putative non-effector PMEs from across the Dothideomycetes. The PME gene family exhibits a small size (up to 5 members per genome) and comprises three major clades. The evolutionary patterns of the PME1 and PME2 clades were largely shaped by duplications and recurring gene retention events, while biased gene loss characterized the small-sized PME3 clade. The presence of five members in the PME gene family of C. cassiicola suggests that the family may play a key role in the evolutionary success of C. cassiicola as a polyphagous plant pathogen. The haplogroups Cc_PME1.1 and Cc_PME1.2 exhibited an accelerated rate of evolution, whereas Cc_PME2.1, Cc_PME2.2, and Cc_PME2.3 seem to be under strong purifying selective constraints. All five PME genes were expressed during infection of soybean leaves, with the highest levels during from six to eight days post-inoculation. The highest relative expression level was measured for CC_29_g7533, a member of the Cc_PME2.3 clade, while the remaining four genes had relatively lower levels of expression.

The Ga1 locus of the genus Zea is associated with novel genome structures derived from multiple, independent non-homologous recombination events.

The Ga1 locus controls cross incompatibility between field corn and popcorn. The Ga1-S haplotype contains two types of pectin methylesterase (PME) genes, ZmPme3 and several copies of ZmGa1P, that are expressed in silk and pollen, respectively. The ga1 haplotype contains non-functional tandem repeat sequences related to ZmPme3 and ZmGa1P. This haplotype can cross pollinate freely and is widely present in field corn. The primary objective of this study is to characterize the repeat sequences from a diverse collection of maize and teosinte lines and use this information to understand the evolution of the Ga1 locus. First, we characterized the complexity of the Ga1 genome region in high quality maize genome assemblies which led to their categorization into five groups based on the number and type of PME-like sequences found at this region. Second, we studied duplication events that led to the ga1 and Ga1-S repeats using maximum-likelihood phylogenetic reconstruction. Divergence estimates of the ga1 haplotype suggest that the duplication events occurred more than 600 kya whereas those in Ga1-S occurred at three time points i.e., > 600 kya, ∼ 260 kya and ∼ 100 kya. These estimates suggest that the ga1 and Ga1-S tandem duplication events occurred independently. Finally, analysis of ZmPme3 and ZmGa1P homologs in Zea and Tripsacum genomes suggests that ga1 and Ga1-S repeats originated from an ancestral pair of PME genes that duplicated and diverged through two evolutionary branches prior to the domestication of maize.

The adaptation of root cell wall pectin to copper toxicity in two citrus species differing in copper tolerance: remodeling and responding.

Citrus species are prone to suffer from copper (Cu) toxicity because of improper application of Cu-based agrochemicals. Copper immobilization mediated by pectin methylesterase (PME) in the root cell wall (CW) is effective for Cu detoxification. However, the underlying mechanisms of the structural modification and stress responses of citrus root CW pectin to Cu toxicity have been less discussed. In the present study, seedlings of 'Shatian pummelo' (Citrus grandis L. Osbeck) and 'Xuegan' (Citrus sinensis L. Osbeck), which differ in Cu tolerance, were irrigated with nutrient solution containing 0.5 (as control), 100, 300 or 500μM Cu for 18 weeks in sandy culture or 24h in hydroponics. At the end of treatments in the 18-week sandy culture, Cu toxicity on CW pectin content, Cu distribution, degree of pectin methylesterification (DPM) and the PME enzyme activity were discussed. At the genome-wide level, PME gene family was identified from the two citrus species, and qRT-PCR array of citrus PMEs under control and 300 μM Cu stress for 18 weeks were performed to screen the Cu-responsive PME genes. Moreover, the candidate genes that responded to Cu toxicity were further examined within 24h. The results showed that Cu toxicity increased the root CW pectin content. The root CW pectin under Cu toxicity was remodeled by upregulation of the expression of the Cu-responsive PME genes followed by increasing PME activity, which mainly promoted low methylesterased pectin level and the Cu content on root CW pectin. Compared with C. sinensis, C. grandis root CW had a lower DPM and higher Cu content on the Cu-stressed root CW pectin, contributing to its higher Cu tolerance. Our present study provided theoretical evidence for root CW pectin remodeling in response to Cu toxicity of citrus species.

Integrated Characterization of Cassava (Manihot esculenta) Pectin Methylesterase (MePME) Genes to Filter Candidate Gene Responses to Multiple Abiotic Stresses.

Plant pectin methylesterases (PMEs) play crucial roles in regulating cell wall modification and response to various stresses. Members of the PME family have been found in several crops, but there is a lack of research into their presence in cassava (Manihot esculent), which is an important crop for world food security. In this research, 89 MePME genes were identified in cassava that were separated into two types (type-Ⅰ and type-Ⅱ) according to the existence or absence of a pro-region (PMEI domain). The MePME gene members were unevenly located on 17 chromosomes, with 19 gene pairs being identified that most likely arose via duplication events. The MePMEs could be divided into ten sub-groups in type-Ⅰ and five sub-groups in type-Ⅱ. The motif analysis revealed 11 conserved motifs in type-Ⅰ and 8 in type-Ⅱ MePMEs. The number of introns in the CDS region of type-Ⅰ MePMEs ranged between one and two, and the number of introns in type-Ⅱ MePMEs ranged between one and nine. There were 21 type-Ⅰ and 31 type-Ⅱ MePMEs that contained signal peptides. Most of the type-Ⅰ MePMEs had two conserved "RK/RLL" and one "FPSWVS" domain between the pro-region and the PME domain. Multiple stress-, hormone- and tissue-specific-related cis-acting regulatory elements were identified in the promoter regions of MePME genes. A total of five co-expressed genes (MePME1, MePME2, MePME27, MePME65 and MePME82) were filtered from different abiotic stresses via the use of UpSet Venn diagrams. The gene expression pattern analysis revealed that the expression of MePME1 was positively correlated with the degree of cassava postharvest physiological deterioration (PPD). The expression of this gene was also significantly upregulated by 7% PEG and 14 °C low-temperature stress, but slightly downregulated by ABA treatment. The tissue-specific expression analysis revealed that MePME1 and MePME65 generally displayed higher expression levels in most tissues than the other co-expressed genes. In this study, we obtain an in-depth understanding of the cassava PME gene family, suggesting that MePME1 could be a candidate gene associated with multiple abiotic tolerance.

Pectin modifications promote haustoria development in the parasitic plant Phtheirospermum japonicum.

Parasitic plants are globally prevalent pathogens with important ecological functions but also potentially devastating agricultural consequences. Common to all parasites is the formation of the haustorium which requires parasite organ development and tissue invasion into the host. Both processes involve cell wall modifications. Here, we investigated a role for pectins during haustorium development in the facultative parasitic plant Phtheirospermum japonicum. Using transcriptomics data from infected Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), we identified genes for multiple P. japonicum pectin methylesterases (PMEs) and their inhibitors (PMEIs) whose expression was upregulated by haustoria formation. Changes in PME and PMEI expression were associated with tissue-specific modifications in pectin methylesterification. While de-methylesterified pectins were present in outer haustorial cells, highly methylesterified pectins were present in inner vascular tissues, including the xylem bridge that connects parasite to host. Specifically blocking xylem bridge formation in the haustoria inhibited several PME and PMEI genes from activating. Similarly, inhibiting PME activity using chemicals or by overexpressing PMEI genes delayed haustoria development. Our results suggest a dynamic and tissue-specific regulation of pectin contributes to haustoria initiation and to the establishment of xylem connections between parasite and host.

Acetylation of inorganic pyrophosphatase by S-RNase signaling induces pollen tube tip swelling by repressing pectin methylesterase.

Self-incompatibility (SI) is a widespread genetically determined system in flowering plants that prevents self-fertilization to promote gene flow and limit inbreeding. S-RNase-based SI is characterized by the arrest of pollen tube growth through the pistil. Arrested pollen tubes show disrupted polarized growth and swollen tips, but the underlying molecular mechanism is largely unknown. Here, we demonstrate that the swelling at the tips of incompatible pollen tubes in pear (Pyrus bretschneideri [Pbr]) is mediated by the SI-induced acetylation of the soluble inorganic pyrophosphatase (PPA) PbrPPA5. Acetylation at Lys-42 of PbrPPA5 by the acetyltransferase GCN5-related N-acetyltransferase 1 (GNAT1) drives accumulation of PbrPPA5 in the nucleus, where it binds to the transcription factor PbrbZIP77, forming a transcriptional repression complex that inhibits the expression of the pectin methylesterase (PME) gene PbrPME44. The function of PbrPPA5 as a transcriptional repressor does not require its PPA activity. Downregulating PbrPME44 resulted in increased levels of methyl-esterified pectins in growing pollen tubes, leading to swelling at their tips. These observations suggest a mechanism for PbrPPA5-driven swelling at the tips of pollen tubes during the SI response. The targets of PbrPPA5 include genes encoding cell wall-modifying enzymes, which are essential for building a continuous sustainable mechanical structure for pollen tube growth.

Pectin methylesterase regulates pollen germination on stigma after pollination in water lily

BackgroundIn the process of interspecific crossing of water lily, the crossing barrier before fertilization is the main reason for the poor seed setting rate of cross breeding, but the specific mechanism is still unclear. The key regulatory genes involved in the interaction between pollen and stigma at 6 h after cross-pollination and self-pollination in water lilies were studied. ResultsFeronia (FER) receptor kinase and respiratory burst oxidase homologue D (RbohD) gene in the regulation pathway of reactive oxygen species (ROS), Calcineurin B-Likes (CBLs), CBL-Interacting protein kinases (CIPKs) and Calcium-dependent protein kinase (CDPKs) in Ca2+signal, and pectin methylesterase (PME) genes may play a key role in the process of mutual recognition between pollen and stigma after cross-pollination of water lilies, which needs further research. ConclusionsWe infer that after cross-pollination, the expression levels of reactive oxygen species and a certain target protein in the stigma papilla cells of water lilies increase through Ca2+ receptors. The target protein alone or together with ROS regulates the increase of PME activity, thus increasing the hardness of the cell wall of the stigma papilla cells and making it difficult for pollen tubes to enter the stigma papilla cells.

Identification and characterization of pectin remodeling gene families in Withania somnifera and their interaction during biotic stress

The Pectin methylesterase (PME), Pectin methylesterase inhibitor (PMEI), and Subtilase (SBT) are pectin remodeling enzymes that play an important role in plant growth and development as well as response to various biotic and abiotic stress conditions. Withania somnifera is an important medicinal plant that gained attention for its phytochemical properties, but relatively little in-depth genomic exploration has been available, including PME, PMEI, and SBT genes. In the present study, 54 PMEs, 19 PMEIs, and 51 SBTs genes were identified from the W. somnifera transcriptome. A detailed phylogeny was performed, followed by a conserved sequence signature analysis, which revealed the major phylogenetic division with Solanum lycopersicum. Insect infestation can cause a significant increase in the functions of these genes, which were identified using PME activity, methanol content, and emission, often by several orders of magnitude. WsPME28, WsPME32, and WsPME50 are putative genes that are significantly upregulated up to six fold during insect infestation, according to gene expression profile analysis. To study specific relative interactions for a PME-SBT pair, molecular docking analysis was performed and found that the serine residue of WsSBT37 interacts with the processing motif (RKLL) of WsPME28 and releases mature PME. As per our best knowledge, this is the first investigation into the identification and characterization of the PME, PMEI, and SBT gene families in W. somnifera. This study will lay the groundwork for future studies targeting these genes, thus giving a better understanding of the stress tolerance mechanism in W. somnifera, and will serve as a reference for determining the most specific SBT-PME pairs in development and stress conditions.

The effect of Aspergillus luchuensis pectin methylesterase genes pmeA and pmeB on methanol production in sweet potato shochu.

To reduce the methanol content in sweet potato shochu, we studied the pectin methylesterase genes of the shochu-koji mold Aspergillus luchuensis. We found the following three homologs of pectin methyleseterase in the genome of A. luchuensis: pmeA, pmeB, and pmeC. Using pectin as a substrate, the methanol-producing activity of the recombinant of each gene expressed in A. luchuensis was examined and found to be present in recombinant PmeA and PmeB. Additionally, small-scale fermentation of sweet potato shochu using disruptions of pmeA and pmeA-pmeB in A. luchuensis (∆pmeA and ∆pmeApmeB) resulted in significant reduction of the methanol content. Taken together, we revealed that the A. luchuensis pmeA gene was mainly involved in methanol production in sweet potato shochu.

Investigation of pectolytic and PR genes expression, quality and phytochemical contents in organic and non-organic table grapes at harvest and during storage

The demand for organic table grapes is increasing worldwide. However, comprehensive information of quality parameters and phytochemical compounds in organically grown fruit remain unclear. Furthermore, table grapes are perishable and postharvest quality retention and waste prevention is very important. In this study we have compared the differences between organic and non-organic table grapes in terms of phytochemical compounds and quality parameters as well as the changes in the expression levels of pathogen related and lytic genes during storage. Organic fruit showed higher levels of phenolics, flavonoids, caffeic acid, hydrogen peroxide, protein content, antioxidant and anti-stress enzymes and total antioxidant activities at harvest and during storage. Although, the expression levels of polygalactronases, pectin methyl esterase, chitinase and glucanase genes was lower in organically grown table grapes at harvest, but the expression of all these genes was significantly increased during cold storage. After 60 days of cold storage the expression levels of pectin methyl esterase, chitinase and glucanase genes was significantly higher than the conventionally grown grape berries in organic ones. The highest expression of polygalacturonase was recorded in organic samples after 30 days of storage. There was no significant difference between the two types of table grapes for decay extension and tissue deterioration rate. The results of this study indicate that due to higher levels of phytochemicals and antioxidant compounds the organic table grapes have a higher nutritional quality. Furthermore, the increase in PR and pectolytic genes expression levels is enough for decreasing the fruit susceptibility to decay pathogens and enhancing the postharvest life of organic grapes.

The cotton pectin methyl esterase gene GhPME21 functions in microspore development and fertility in Gossypium hirsutum L.

Pectin widely exists in higher plants' cell walls and intercellular space of higher plants and plays an indispensable role in plant growth and development. We identified 55 differentially expressed genes related to pectin degradation by transcriptomic analysis in the male sterile mutant, ms1. A gene encoding pectin methylesterase (GhPME21) was found to be predominantly expressed in the developing stamens of cotton but was significantly down-regulated in ms1 stamens. The tapetal layer of GhPME21 interfered lines (GhPME21i) was significantly thickened compared to that of WT at the early stage; anther compartment morphology of GhPME21i lines was abnormal, and the microspore wall was broken at the middle stage; Alexander staining showed that the pollen grains of GhPME21i lines differed greatly in volume at the late stage. The mature pollen surfaces of GhPME21i lines were deposited with discontinuous and broken sheets and prickles viewed under SEM. Fewer pollen tubes were observed to germinate in vitro in GhPME21i lines, while tiny of those in vivo were found to elongate to the ovary. The seeds harvested from GhPME21i lines as pollination donors were dry and hollow. The changes of phenotypes in GhPME21i lines at various stages illustrated that the GhPME21 gene played a vital role in the development of cotton stamens and controlled plant fertility by affecting stamen development, pollen germination, and pollen tube elongation. The findings of this study laid the groundwork for further research into the molecular mechanisms of PMEs involved in microspore formation and the creation of cotton male sterility materials.

Genome and Transcriptome Identification of a Rice Germplasm with High Cadmium Uptake and Translocation.

The safe production of food on Cd-polluted land is an urgent problem to be solved in South China. Phytoremediation or cultivation of rice varieties with low Cd are the main strategies to solve this problem. Therefore, it is very important to clarify the regulatory mechanism of Cd accumulation in rice. Here, we identified a rice variety with an unknown genetic background, YSD, with high Cd accumulation in its roots and shoots. The Cd content in the grains and stalks were 4.1 and 2.8 times that of a commonly used japonica rice variety, ZH11, respectively. The Cd accumulation in the shoots and roots of YSD at the seedling stage was higher than that of ZH11, depending on sampling time, and the long-distance transport of Cd in the xylem sap was high. Subcellular component analysis showed that the shoots, the cell wall, organelles, and soluble fractions of YSD, showed higher Cd accumulation than ZH11, while in the roots, only the cell wall pectin showed higher Cd accumulation. Genome-wide resequencing revealed mutations in 22 genes involved in cell wall modification, synthesis, and metabolic pathways. Transcriptome analysis in Cd-treated plants showed that the expression of pectin methylesterase genes was up-regulated and the expression of pectin methylesterase inhibitor genes was down-regulated in YSD roots, but there were no significant changes in the genes related to Cd uptake, translocation, or vacuole sequestration. The yield and tiller number per plant did not differ significantly between YSD and ZH11, but the dry weight and plant height of YSD were significantly higher than that of ZH11. YSD provides an excellent germplasm for the exploration of Cd accumulation genes, and the cell wall modification genes with sequence- and expression-level variations provide potential targets for phytoremediation.

A single silk- and multiple pollen-expressed PMEs at the Ga1 locus modulate maize unilateral cross-incompatibility.

The Gametophyte factor1 (Ga1) locus in maize confers unilateral cross-incompatibility (UCI), and it is controlled by both pollen and silk-specific determinants. Although the Ga1 locus has been reported for more than a century and is widely utilized in maize breeding programs, only the pollen-specific ZmGa1P has been shown to function as a male determinant; thus, the genomic structure of the Ga1 locus and all the determinants that control UCI at this locus have not yet been fully characterized. Here, we used map-based cloning to confirm the determinants of UCI at the Ga1 locus and maize pan-genome sequence data to characterize the genomic structure of the Ga1 locus. The Ga1 locus comprises one silk-expressed pectin methylesterase gene (PME) (ZmGa1F) and eight pollen-expressed PMEs (ZmGa1P and ZmGa1PL1-7). Knockout of ZmGa1F in Ga1/Ga1 lines leads to the complete loss of the female barrier function. The expression of individual ZmGa1PL genes in a ga1/ga1 background endows ga1 pollen with the ability to overcome the female barrier of the Ga1 locus. These findings, combined with genomic data and genetic analyses, indicate that the Ga1 locus is modulated by a single female determinant and multiple male determinants, which are tightly linked. The results of this study provide valuable insights into the genomic structure of the Ga2 and Tcb1 loci and will aid applications of these loci in maize breeding programs.

Ovule cell wall composition is a maternal determinant of grain size in barley.

In cereal species, seed and grain size is influenced by growth of the ovule integuments (seed coat), the spikelet hull (lemma and palea) and the filial endosperm. It has remained unclear whether a highly conserved ovule tissue, the nucellus, has any impact on grain size. Immunolabelling revealed that the barley nucellus comprises two distinct cell types that differ in terms of cell wall homogalacturonan (HG) accumulation. Transcriptional profiling of the nucellus identified two pectin methylesterase genes, OVULE PECTIN MODIFIER 1 (OPM1) and OPM2, which are expressed in the ovule but absent from the seed. Ovules from an opm1 opm2 mutant, and plants expressing an ovule-specific pectin methylesterase inhibitor (PMEI), exhibit reduced HG accumulation. This results in changes to ovule cell size and shape, and ovules that are longer than wild-type controls. At grain maturity, this is manifested as significantly longer grain. These findings indicate that cell wall composition during ovule development acts to limit ovule and seed growth. The investigation of ovule PME and PMEI activity reveals an unexpected role of maternal tissues in controlling grain growth prior to fertilisation, one that has been lacking from models exploring improvements in grain size.