Endosperm Development Research Articles

Visualizing the spatial distribution of functional metabolites in Forsythia suspensa at different harvest stages by MALDI mass spectrometry imaging

As a traditional Chinese medicine, Forsythia suspensa (F. suspensa) has attracted much attention due to its significant pharmacological activity. Revealing the spatial distribution of metabolites during F. suspensa development is important for understanding its biosynthesis rules and improving the quality of medicinal materials. However, there is currently a lack of information on the spatial distribution of F. suspensa metabolites. In this work, the spatial distribution and growth metabolism patterns of important metabolites of F. suspensa were studied for the first time using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Using 2,5-dimethylnaphthalene (DAN) as the matrix and detecting in negative ion mode, the spatial distribution and growth patterns of 11 metabolites obtained from longitudinal sections of F. suspensa included pinoresinol, phillygenin, forsythoside A, forsythoside E, rutin, caffeic acid, malic acid, citric acid, stearic acid, oleic acid, and linoleic acid. These results showed the mesocarp and endosperm tissues of F. suspensa were important for storing important functional metabolites. Changes in mesocarp and endosperm growth and development tissues caused large changes in the content of important functional metabolites in F. suspensa. These results provide a basis for understanding the spatial distribution of metabolites in F. suspensa tissues and the significant changes that occur during growth and development, exploring the mechanism of important synthesis of metabolites, regulating the harvest of F. suspensa, and improving the quality of medicinal herbs.

The small PPR protein SPR2 interacts with PPR-SMR1 to facilitate the splicing of introns in maize mitochondria.

Splicing of plant mitochondrial introns is facilitated by numerous nucleus-encoded protein factors. Although some splicing factors have been identified in plants, the mechanism underlying mitochondrial intron splicing remains largely unclear. In this study, we identified a small P-type pentatricopeptide repeat (PPR) protein containing merely four PPR repeats, small PPR protein 2 (SPR2), which is required for the splicing of more than half of the introns in maize (Zea mays) mitochondria. Null mutations of Spr2 severely impair the splicing of 15 out of the 22 mitochondrial Group II introns, resulting in substantially decreased mature transcripts, which abolished the assembly and activity of mitochondrial complex I. Consequently, embryogenesis and endosperm development were arrested in the spr2 mutants. Yeast two-hybrid, luciferase complementation imaging, bimolecular fluorescence complementation, and semi-in vivo pull-down analyses indicated that SPR2 interacts with small MutS-related domain protein PPR-SMR1, both of which are required for the splicing of 13 introns. In addition, SPR2 and/or PPR-SMR1 interact with other splicing factors, including PPR proteins EMPTY PERICARP16, PPR14, and chloroplast RNA splicing and ribosome maturation (CRM) protein Zm-mCSF1, which participate in the splicing of specific intron(s) of the 13 introns. These results prompt us to propose that SPR2/PPR-SMR1 serves as the core component of a splicing complex and possibly exerts the splicing function through a dynamic interaction with specific substrate recognizing PPR proteins in mitochondria.

Low Light Stress Increases Chalkiness by Disturbing Starch Synthesis and Grain Filling of Rice

Low light stress increases the chalkiness of rice; however, this effect has not been fully characterized. In this study, we demonstrated that low light resulted in markedly decreased activity of ADP-glucose pyrophosphorylase in the grains and those of sucrose synthase and soluble starch synthase in the early period of grain filling. Furthermore, low light also resulted in decreased activities of granule-bound starch synthase and starch branching enzyme in the late period of grain filling. Therefore, the maximum and mean grain filling rates were reduced but the time to reach the maximum grain filling rates and effective grain filling period were increased by low light. Thus, it significantly decreased the grain weight at the maximum grain filling rate and grain weight and retarded the endosperm growth and development, leading to a loose arrangement of the amyloplasts and an increase in the chalkiness of the rice grains. Compared to the grains at the top panicle part, low light led to a greater decrease in the grain weight at the maximum grain filling rate and time to reach the grain weight at the maximum grain filling rate at the bottom panicle part, which contributed to an increase in chalkiness by increasing the rates of different chalky types at the bottom panicle part. In conclusion, low light disturbed starch synthesis in grains, thereby impeding the grain filling progress and increasing chalkiness, particularly for grains at the bottom panicle part.

Network and Evolutionary Analysis Reveals Candidate Genes of Membrane Trafficking Involved in Maize Seed Development and Immune Response

The plant membrane-trafficking system plays a crucial role in maintaining proper cellular functions and responding to various developmental and environmental cues. Thus far, our knowledge of the maize membrane-trafficking system is still limited. In this study, we systematically identified 479 membrane-trafficking genes from the maize genome using orthology search and studied their functions by integrating transcriptome and evolution analyses. These genes encode the components of coated vesicles, AP complexes, autophagy, ESCRTs, retromers, Rab GTPases, tethering factors, and SNAREs. The maize genes exhibited diverse but coordinated expression patterns, with 249 genes showing elevated expression in reproductive tissues. Further WGCNA analysis revealed that five COPII components and four Rab GTPases had high connectivity with protein biosynthesis during endosperm development and that eight components of autophagy, ESCRT, Rab, and SNARE were strongly co-upregulated with defense-related genes and/or with secondary metabolic processes to confer basal resistance to Fusarium graminearum. In addition, we identified 39 membrane-trafficking genes with strong selection signals during maize domestication and/or improvement. Among them, ZmSec23a and ZmVPS37A were selected for kernel oil production during improvement and pathogen resistance during domestication, respectively. In summary, these findings will provide important hints for future appreciation of the functions of membrane-trafficking genes in maize.

FLOURY ENDOSPERM20 encoding SHMT4 is required for rice endosperm development.

FLOURY ENDOSPERM20 encoding SHMT4 is required for rice endosperm development.

The structures of floral organs and reproductive characteristics of an ornamental bamboo species, Pleioblastus pygmaeus

As a woody grass, bamboo has special reproductive habits with an extremely long vegetative phase. Pleioblastus pygmaeus is a kind of ornamental dwarf bamboo species with high ecological and economic value in China. There was no documentary record of the flowering of P. pygmaeus until 2015, which bloomed in the Bamboo Garden of Nanjing Forestry University. Generally, bamboo plants rarely bear fruit or have a low seed setting rate, but this species has a high seed production. This study explores developmental reasons using anatomical methods. The process of flower bud differentiation and a series of important reproductive development processes including anther wall development, microsporogenesis, megasporogenesis, male and female gametophyte development, and embryonic development were investigated sequentially. Each stamen contained three tetrasporangiate anthers and the development of anther wall was of Monocotyledonous type. The microspores finally matured into 3-celled pollen grains by two successive mitoses. The pistil was composed of three carpels, with an anatropous, tenuinucellate and bitegmic ovule in a single ovary. The formation of embryo sac belonged to Polygonum type. With three mitoses, functional megaspore developed into the embryo sac with eight nuclei within seven cells. The development of stamen and pistil was synchronous in the same floret. The development of embryo followed Grass type and the development of endosperm belonged to Nuclear type. The development of endosperm was earlier than that of embryo. The study enriches basic knowledge of reproductive biology of bamboo plants and is of great fundamental significance to furtherly explore flowering mechanism of P. pygmaeus and to cultivate bamboo plants sustainably.

BABY BOOM regulates early embryo and endosperm development.

The BABY BOOM (BBM) AINTEGUMENTA-LIKE (AIL) AP2/ERF domain transcription factor is a major regulator of plant cell totipotency, as it induces asexual embryo formation when ectopically expressed. Surprisingly, only limited information is available on the role of BBM during zygotic embryogenesis. Here we reexamined BBM expression and function in the model plant Arabidopsis thaliana (Arabidopsis) using reporter analysis and newly developed CRISPR mutants. BBM was expressed in the embryo from the zygote stage and also in the maternal (nucellus) and filial (endosperm) seed tissues. Analysis of CRISPR mutant alleles for BBM (bbm-cr) and the redundantly acting AIL gene PLETHORA2 (PLT2) (plt2-cr) uncovered individual roles for these genes in the timing of embryo progression. We also identified redundant roles for BBM and PLT2 in endosperm proliferation and cellularization and the maintenance of zygotic embryo development. Finally, we show that ectopic BBM expression in the egg cell of Arabidopsis and the dicot crops Brassica napus and Solanum lycopersicon is sufficient to bypass the fertilization requirement for embryo development. Together these results highlight roles for BBM and PLT2 in seed development and demonstrate the utility of BBM genes for engineering asexual embryo development in dicot species.

Influence of high-molecular-weight glutenin subunit deletions at the Glu-A1 and Glu-D1 loci on protein body development, protein components and dough properties of wheat (Triticum aestivum L.)

High-molecular-weight glutenin subunits (HMW-GSs) play a critical role in determining the viscoelastic properties of wheat. As the organelle where proteins are stored, the development of protein bodies (PBs) reflects the status of protein synthesis and also affects grain quality to a great extent. In this study, with special materials of four near-isogenic lines in a Yangmai 18 background we created, the effects of Glu-A1 and Glu-D1 loci deletions on the development and morphological properties of the protein body, protein components and dough properties were investigated. The results showed that the deletion of the HMW-GS subunit delayed the development process of the PBs, and slowed the increases of volume and area of PBs from 10 days after anthesis (DAA) onwards. In contrast, the areas of PBs at 25 DAA, the middle or late stage of endosperm development, showed no distinguishable differences among the four lines. Compared to the wild type and single null type in Glu-A1, the ratios of HMW-GSs to low-molecular-weight glutenin subunits (LMW-GSs), glutenin macropolymer (GMP) content, mixograph parameters as well as extension parameters decreased in the single null type in Glu-D1 and double null type in Glu-A1 and Glu-D1, while the ratios of gliadins (Gli)/glutenins (Glu) in those types increased. The absence of Glu-D1 subunits decreased both dough strength and extensibility significantly compared to the Glu-A1 deletion type. These results provide a detailed description of the effect of HMW-GS deletion on PBs, protein traits and dough properties, and contribute to the utilization of Glu-D1 deletion germplasm in weak gluten wheat improvement for use in cookies, cakes and southern steamed bread in China and liquor processing.

The Function of DNA Demethylase Gene ROS1a Null Mutant on Seed Development in Rice (Oryza Sativa) Using the CRISPR/CAS9 System.

The endosperm is the main nutrient source in cereals for humans, as it is a highly specialized storage organ for starch, lipids, and proteins, and plays an essential role in seed growth and development. Active DNA demethylation regulates plant developmental processes and is ensured by cytosine methylation (5-meC) DNA glycosylase enzymes. To find out the role of OsROS1a in seed development, the null mutant of OsROS1a was generated using the CRISPR/Cas9 system. The null mutant of OsROS1a was stable and heritable, which affects the major agronomic traits, particularly in rice seeds. The null mutant of OsROS1a showed longer and narrower grains, and seeds were deformed containing an underdeveloped and less-starch-producing endosperm with slightly irregularly shaped embryos. In contrast to the transparent grains of the wild type, the grains of the null mutant of OsROS1a were slightly opaque and rounded starch granules, with uneven shapes, sizes, and surfaces. A total of 723 differential expression genes (DEGs) were detected in the null mutant of OsROS1a by RNA-Seq, of which 290 were downregulated and 433 were upregulated. The gene ontology (GO) terms with the top 20 enrichment factors were visualized for cellular components, biological processes, and molecular functions. The key genes that are enriched for these GO terms include starch synthesis genes (OsSSIIa and OsSSIIIa) and cellulose synthesis genes (CESA2, CESA3, CESA6, and CESA8). Genes encoding polysaccharides and glutelin were found to be downregulated in the mutant endosperm. The glutelins were further verified by SDS-PAGE, suggesting that glutelin genes could be involved in the null mutant of OsROS1a seed phenotype and OsROS1a could have the key role in the regulation of glutelins. Furthermore, 378 differentially alternative splicing (AS) genes were identified in the null mutant of OsROS1a, suggesting that the OsROS1a gene has an impact on AS events. Our findings indicated that the function on rice endosperm development in the null mutant of OsROS1a could be influenced through regulating gene expression and AS, which could provide the base to properly understand the molecular mechanism related to the OsROS1a gene in the regulation of rice seed development.

Starch Biosynthetic Protein Complex Formation in Rice ss2a be2b (+) Double Mutant Differs from Their Parental Single Mutants.

Amylopectin, which consists of highly branched glucose polymers, is a major component of starch. Biochemical processes that regulate the elongation of glucose polymers and the generation and removal of glucose branches are essential for determining the properties of starch. Starch synthases (SSs) and branching enzyme (BE) mainly form complexes consisting of SSI, SSIIa, and BEIIb during endosperm development. Loss of BEIIb in rice is complemented by BEIIa, but the compensatory effects differ depending on the presence or absence of inactive BEIIb. To better understand these compensatory mechanisms, ss2a be2b (+) double mutant, which possessed truncated inactive SSIIa and inactive BEIIb, were analyzed. Soluble proteins separated by gel filtration chromatography showed that SSIIa and BEIIb proteins in the wild-type exhibited a broad range of elution patterns and only small amounts were detected in high molecular mass fractions. In contrast, most of truncated inactive SSIIa and inactive BEIIb from ss2a be2b (+) were found in high molecular mass fractions, and the SSI-SSIIa-BEIIb trimeric protein complex found in the wild-type was likely absent in ss2a be2b (+). Those SSIIa and BEIIb proteins in high molecular mass fractions in ss2a be2b (+) were also identified by mass spectrometry. Parental ss2a single mutant had negligible amounts of SSIIa suggesting that the truncated inactive SSIIa was recruited to high-molecular mass complexes in the presence of inactive BEIIb in ss2a be2b (+) double mutant. In addition, SSIVb might be involved in the formation of alternative protein complexes with < 300 kDa in ss2a be2b (+).

Identification and Clarification of VrCYCA1: A Key Genic Male Sterility-Related Gene in Mungbean by Multi-Omics Analysis

Heterosis has been utilized in crops for a long time, and although crop fertility is the basis for the utilization of heterosis, there is limited information concerning the genic male sterility (GMS) of mungbean. Therefore, based on the genic male sterile mutant, M1, obtained by EMS mutagenesis of the Weilyu cultivar, this project used multi-omics analysis to detect the male sterile site and further identify its candidate gene, and then the mechanism of the candidate gene was discussed. As a result, one locus region (Chr5: 6,835,001–6,935,000 bp) associated with GMS was identified, and nine genes were found within the 100 Kb region. The candidate gene, VrCYCA1, around the above loci had a TATA box deletion approximately 4.7 Kb upstream of the gene, and this was evidenced by comparative genomics, transcriptome analysis, and RT-qPCR analysis. The expression level of VrCYCA1 was significantly downregulated (log2FC = −2.06, p-value = 0.025) in the ms lines compared with the control group. Moreover, 6653 genes showed differential expression between the Weilyu lines and mutant lines as well as 165 metabolites with significant differences in their concentration levels. Among those differentially expresses genes, 226 were annotated with functional categories involved in flowering and endosperm development, and six genes had protein–protein interactions with VrCYCA1. Seven categories of metabolites and seven genes participated in the relationship between reproductive growth and vegetative growth, which might have caused the sterility of mungbean in the mutant plants. This study used multi-omics data to mine a mungbean GMS-related gene, VrCYCA1, and constructed a GMS genetic network to explore the molecular mechanism of VrCYCA1. The results lay a solid foundation for further molecular biology research and utilization in mungbean male sterility.

The OsEIL1-OsERF115-target gene regulatory module controls grain size and weight in rice.

SummaryGrain size is one of the essential determinants of rice yield. Our previous studies revealed that ethylene plays an important role in grain‐size control; however, the precise mechanism remains to be determined. Here, we report that the ethylene response factor OsERF115 functions as a key downstream regulator for ethylene‐mediated grain development. OsERF115 encodes an AP2/ERF‐type transcriptional factor that is specifically expressed in young spikelets and developing caryopses. Overexpression of OsERF115 significantly increases grain length, width, thickness and weight by promoting longitudinal elongation and transverse division of spikelet hull cells, as well as enhancing grain‐filling activity, whereas its knockout mutations lead to the opposite effects, suggesting that OsERF115 positively regulates grain size and weight. OsERF115 transcription is strongly induced by ethylene, and OsEIL1 directly binds to the promoter to activate its expression. OsERF115 acts as a transcriptional repressor to directly or indirectly modulate a set of grain‐size genes during spikelet growth and endosperm development. Importantly, haplotype analysis reveals that the SNP variations in the EIN3‐binding sites of OsERF115 promoter are significantly associated with the OsERF115 expression levels and grain weight, suggesting that natural variations in the OsERF115 promoter contribute to grain‐size diversity. In addition, the OsERF115 orthologues are identified only in grass species, implying a conserved and unique role in the grain development of cereal crops. Our results provide insights into the molecular mechanism of ethylene‐mediated grain‐size control and a potential strategy based on the OsEIL1‐OsERF115‐target gene regulatory module for genetic improvement of rice yield.

Riboflavin integrates cellular energetics and cell cycle to regulate maize seed development.

SummaryRiboflavin is the precursor of essential cofactors for diverse metabolic processes. Unlike animals, plants can de novo produce riboflavin through an ancestrally conserved pathway, like bacteria and fungi. However, the mechanism by which riboflavin regulates seed development is poorly understood. Here, we report a novel maize (Zea mays L.) opaque mutant o18, which displays an increase in lysine accumulation, but impaired endosperm filling and embryo development. O18 encodes a rate‐limiting bifunctional enzyme ZmRIBA1, targeted to plastid where to initiate riboflavin biosynthesis. Loss of function of O18 specifically disrupts respiratory complexes I and II, but also decreases SDH1 flavinylation, and in turn shifts the mitochondrial tricarboxylic acid (TCA) cycle to glycolysis. The deprivation of cellular energy leads to cell‐cycle arrest at G1 and S phases in both mitosis and endoreduplication during endosperm development. The unexpected up‐regulation of cell‐cycle genes in o18 correlates with the increase of H3K4me3 levels, revealing a possible H3K4me‐mediated epigenetic back‐up mechanism for cell‐cycle progression under unfavourable circumstances. Overexpression of O18 increases riboflavin production and confers osmotic tolerance. Altogether, our results substantiate a key role of riboflavin in coordinating cellular energy and cell cycle to modulate maize endosperm development.

Characterization of Transcription Regulatory Domains of OsMADS29: Identification of Proximal Auxin-Responsive Domains and a Strong Distal Negative Element.

OsMADS29 (M29) is a seed-specific MADS-box transcription factor involved in programmed cell death of nucellar tissue and maintaining auxin:cytokinin homeostasis. It affects embryo and endosperm development and starch filling during seed development in rice. Its expression seems to be tightly regulated by developmental, spatial, and temporal cues; however, cis- and trans-regulatory factors that affect its expression are largely unknown. In silico analysis of the 1.7 kb upstream regulatory region (URR) consisting of 1,290 bp promoter and 425 bp 5′-UTR regions revealed several auxin-responsive and seed-specific cis-regulatory elements distributed across the URR. In this study, the analysis of four URR deletions fused to a downstream β-glucuronidase (GUS) reporter in transgenic rice has revealed the presence of several proximal positive elements and a strong distal negative element (NE). The promoter regions containing auxin-responsive elements responded positively to the exogenous application of auxins to transgenic seedlings. The proximal positive elements are capable of driving reporter expression in both vegetative and reproductive tissues. In contrast, the NE strongly suppresses reporter gene expression in both vegetative and reproductive tissues. In a transient onion peel assay system, the NE could reduce the efficacy of a 2x CaMV 35S promoter by ∼90%. Our results indicate the existence of a complex array of positive and negative regulatory regions along with auxin-responsive elements guiding the development-dependent and spatial expression of M29.

Histone Modification and Chromatin Remodeling During the Seed Life Cycle.

Seeds are essential for the reproduction and dispersion of spermatophytes. The seed life cycle from seed development to seedling establishment proceeds through a series of defined stages regulated by distinctive physiological and biochemical mechanisms. The role of histone modification and chromatin remodeling in seed behavior has been intensively studied in recent years. In this review, we summarize progress in elucidating the regulatory network of these two kinds of epigenetic regulation during the seed life cycle, especially in two model plants, rice and Arabidopsis. Particular emphasis is placed on epigenetic effects on primary tissue formation (e.g., the organized development of embryo and endosperm), pivotal downstream gene expression (e.g., transcription of DOG1 in seed dormancy and repression of seed maturation genes in seed-to-seedling transition), and environmental responses (e.g., seed germination in response to different environmental cues). Future prospects for understanding of intricate interplay of epigenetic pathways and the epigenetic mechanisms in other commercial species are also proposed.

Effects of TaMTL-Edited Mutations on Grain Phenotype and Storage Component Composition in Wheat

Wheat nutrition and processing-quality are primarily based on the endosperm ingredients. However, the effect of embryos on grain traits and components remains unclear. In this study, we found that in the cross-pollinated and self-pollinated progenies of the four wheat mtl mutants (mtl-A, mtl-AD, mtl-BD, and mtl-ABD) the haploid induction rates were 0–15.6% and 0–14.1%, and the embryo abortion rates were 0–27.4% and 0–24.1%, respectively, in which mtl-A had no effect on haploid induction and embryo development. The embryoless grains (ELG) were comparable to the normal grains (NG) from mtl-AD, mtl-BD, and mtl-ABD in grain length, grain width and thousand-kernel weight, but the grain traits were significantly less than those in NG from mutant mtl-A. During grain filling period, mtl-ABD had similar ELG ratio and amount of starch granule (SG) and protein body (PB) in ELG and NG. At maturity stage, the morphological features of A-type and B-type SG in ELG were similar to those in NG in mtl mutants; however, amylose, gliadin, and glutenin contents were higher in ELG, and total starch, albumin and globulin contents were higher in NG. Our results clarified the effect of the wheat mtl mutants on haploid induction and grain traits and nutrition composition in this crop, and provided new clues for studying the development of embryo and endosperm and their interaction in plants.

SWI2/SNF2 chromatin remodeling ATPases SPLAYED and BRAHMA control embryo development in rice.

Chromatin remodeling ATPases OsSYD and OsBRM are involved in shoot establishment, and both affect OSH gene transcription. OsSYD protein interacts with RFL, but OsBRM does not. In plants, SPLAYED (SYD) and BRAHMA (BRM) encode chromatin remodeling ATPases that use the energy derived from ATP hydrolysis to restructure nucleosomes and render certain genomic regions available to transcription factors. However, the function of SYD and BRM on rice growth and development is unknown. Here, we constructed ossyd and osbrm mutants using CRISPR/Cas9 technology and analyzed the effects of mutations on rice embryo development. We discovered that the ossyd and osbrm mutants exhibited severe defects during embryonic development, whereas endosperm development was normal. These results indicated that the development of the embryo and endosperm is independent of each other. Consequently, the ossyd- and osbrm-null mutants did not germinate due to the abnormal embryos. Furthermore, we observed the embryos of ossyd- and osbrm-null mutants, and they indeed had distinct differentiation defects in shoot establishment, acquired during embryogenesis. To verify the function of OsSYD and OsBRM in embryogenesis, we measured the transcript levels of marker genes at different stages. Compared with wild type, the expression levels of multiple OSH genes were significantly reduced in the mutants, which was consistent with the defective shoot establishment phenotypes. The interaction between SYD and RICE FLORICAULA/LFY (RFL) was revealed using a yeast two-hybrid screening system, suggesting that the interaction between the LFY homolog and chromatin remodeling ATPases is ubiquitous in plants. Collectively, our findings provide the basis for elucidating the function of OsSYD and OsBRM during embryo development in rice.

EMP80 mediates the C-to-U editing of nad7 and atp4 and interacts with ZmDYW2 in maize mitochondria.

RNA C-to-U editing is important to the expression and function of organellar genes in plants. Although several families of proteins have been identified to participate in this process, the underlying mechanism is not fully understood. Here we report the function of EMP80 in the C-to-U editing at the nad7-769 and atp4-118 sites, and the potential recruitment of ZmDYW2 as a trans deaminase in maize (Zea mays) mitochondria. Loss of EMP80 function arrests embryogenesis and endosperm development in maize. EMP80 is a PPR-E+ protein localised to mitochondria. An absence of EMP80 abolishes the C-to-U RNA editing at nad7-769 and atp4-118 sites, resulting in a cysteine-to-arginine (Cys→Arg) change in Nad7 and Atp4 in the emp80 mutant. The amino acid change consequently reduces the assembly of complexes I and V, leading to an accumulation of the F1 subcomplex of complex V. EMP80 was found to interact with atypical DYW-type PPR protein ZmDYW2, which interacts with ZmNUWA. Co-expression of ZmNUWA enhances the interaction between EMP80 and ZmDYW2, suggesting that EMP80 potentially recruits ZmDYW2 as a trans deaminase through protein-protein interaction, and ZmNUWA may function as an enhancer of this interaction.

DEK48 Is Required for RNA Editing at Multiple Mitochondrial Sites and Seed Development in Maize.

In flowering plants, C-to-U RNA editing can be critical to normal functions of mitochondrion-encoded proteins. Mitochondrial C-to-U RNA editing is facilitated by many factors from diverse protein families, of which the pentatricopeptide repeat (PPR) proteins play an important role. Owing to their large number and frequent embryo lethality in mutants, functions of many PPRs remain unknown. In this study, we characterized a mitochondrion-localized DYW-type PPR protein, DEK48, functioning in the C-to-U RNA editing at multiple mitochondrial transcripts in maize. Null mutation of Dek48 severely arrests embryo and endosperm development, causing a defective kernel (dek) phenotype, named dek48. DEK48 loss of function abolishes the C-to-U editing at nad3-185, -215, and nad4-376, -977 sites and decreases the editing at 11 other sites, resulting in the alteration of the corresponding amino acids. Consequently, the absence of editing caused reduced assembly and activity of complex I in dek48. Interestingly, we identified a point mutation in dek48-3 causing a deletion of the Tryptophan (W) residue in the DYW motif that abolishes the editing function. In sum, this study reveals the function of DEK48 in the C-to-U editing in mitochondrial transcripts and seed development in maize, and it demonstrates a critical role of the W residue in the DYW triplet motif of DEK48 for the C-to-U editing function in vivo.

Maize Endosperm Development: Tissues, Cells, Molecular Regulation and Grain Quality Improvement

Maize endosperm plays important roles in human diet, animal feed and industrial applications. Knowing the mechanisms that regulate maize endosperm development could facilitate the improvement of grain quality. This review provides a detailed account of maize endosperm development at the cellular and histological levels. It features the stages of early development as well as developmental patterns of the various individual tissues and cell types. It then covers molecular genetics, gene expression networks, and current understanding of key regulators as they affect the development of each tissue. The article then briefly considers key changes that have occurred in endosperm development during maize domestication. Finally, it considers prospects for how knowledge of the regulation of endosperm development could be utilized to enhance maize grain quality to improve agronomic performance, nutrition and economic value.