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Castor (Ricinus communis L.) seeds produce abundant ricinoleic acid during seed maturation, which is important for plant development and human demands. Ricinoleic acid, as a unique hydroxy fatty acid (HFA), possesses a distinct bond structure that could be used as a substitute for fossil fuels. Here, we identified all homologous genes related to glycolysis, hydroxy fatty acid biosynthesis, and triacylglycerol (TAG) accumulation in castor seeds. Furthermore, we investigated their expression patterns globally during five seed development stages. We characterized a total of 66 genes involved in the glycolysis pathway, with the majority exhibiting higher expression levels during the early stage of castor bean seed development. This metabolic process provided abundant acetyl-CoA for fatty acid (FA) biosynthesis. Subsequently, we identified 82 genes involved in the processes of de novo FA biosynthesis and TAG assembly, with the majority exhibiting high expression levels during the middle or late stages. In addition, we examined the expression patterns of the transcription factors involved in carbohydrate and oil metabolism. For instance, RcMYB73 and RcERF72 exhibited high expression levels during the early stage, whereas RcWRI1, RcABI3, and RcbZIP67 showed relatively higher expression levels during the middle and late stages, indicating their crucial roles in seed development and oil accumulation. Our study suggests that the high HFA production in castor seeds is attributed to the interaction of multiple genes from sugar transportation to lipid droplet packaging. Therefore, this research comprehensively characterizes all the genes related to glycolysis, fatty acid biosynthesis, and triacylglycerol (TAG) accumulation in the castor and provides novel insight into exploring the genetic mechanisms underlying seed oil accumulation in the endosperm of castor beans. [ABSTRACT FROM AUTHOR]

Background: Understanding the processes governing angiosperm seed growth and development is essential both for fundamental plant biology and for agronomic purposes. Master regulators of angiosperm seed development are expressed in a seed-specific manner. However, it is unclear how this seed specificity of transcription is established. In some vertebrates, DNA methylation valleys (DMVs) are highly conserved and strongly associated with key developmental genes, but comparable studies in plants are limited to Arabidopsis and soybean. Castor bean (Ricinus communis) is a valuable model system for the study of seed biology in dicots and source of economically important castor oil. Unlike other dicots such as Arabidopsis and soybean, castor bean seeds have a relatively large and persistent endosperm throughout seed development, representing substantial structural differences in mature seeds. Here, we performed an integrated analysis of RNA-seq, whole-genome bisulfite sequencing, and ChIP-seq for various histone marks in the castor bean. Results: We present a gene expression atlas covering 16 representative tissues and identified 1162 seed-specific genes in castor bean (Ricinus communis), a valuable model for the study of seed biology in dicots. Upon whole-genome DNA methylation analyses, we detected 32,567 DMVs across five tissues, covering ~33% of the castor bean genome. These DMVs are highly hypomethylated during development and conserved across plant species. We found that DMVs have the potential to activate transcription, especially that of tissue-specific genes. Focusing on seed development, we found that many key developmental regulators of seed/endosperm development, including AGL61, AGL62, LEC1, LEC2, ABI3, and WRI1, were located within DMVs. ChIP-seq for five histone modifications in leaves and seeds clearly showed that the vast majority of histone modification peaks were enriched within DMVs, and their remodeling within DMVs has a critical role in the regulation of seed-specific gene expression. Importantly, further experiment analysis revealed that distal DMVs may act as cis-regulatory elements, like enhancers, to activate downstream gene expression. Conclusions: Our results point to the importance of DMVs and special distal DMVs behaving like enhancers, in the regulation of seed-specific genes, via the reprogramming of histone modifications within DMVs. Furthermore, these results provide a comprehensive understanding of the epigenetic regulator roles in seed development in castor bean and other important crops. [ABSTRACT FROM AUTHOR]

Background: Little is known about the molecular basis of seed size formation in endospermic seed of dicotyledons. The seed of castor bean (Ricinus communis L.) is considered as a model system in seed biology studies because of its persistent endosperms throughout seed development. Results: We compared the size of endosperm and endospermic cells between ZB107 and ZB306 and found that the larger seed size of ZB107 resulted from a higher cell count in the endosperm, which occupy a significant amount of the total seed volume. In addition, fresh weight, dry weight, and protein content of seeds were remarkably higher in ZB107 than in ZB306. Comparative proteomic and transcriptomic analyses were performed between large-seed ZB107 and small-seed ZB306, using isobaric tags for relative and absolute quantification (iTRAQ) and RNA-seq technologies, respectively. A total of 1416 protein species were identified, of which 173 were determined as differentially abundant protein species (DAPs). Additionally, there were 9545 differentially expressed genes (DEGs) between ZB306 and ZB107. Functional analyses revealed that these DAPs and DEGs were mainly involved in cell division and the metabolism of carbohydrates and proteins. Conclusions: These findings suggest that both cell number and storage-component accumulation are critical for the formation of seed size, providing new insight into the potential mechanisms behind seed size formation in endospermic seeds. [ABSTRACT FROM AUTHOR]

The basic leucine zipper (bZIP) transcription factors comprise a family of transcriptional regulators present extensively in plants, involved in regulating diverse biological processes such as flower and vascular development, seed maturation, stress signaling and pathogen defense. Castor bean ( Ricinus communis L. Euphorbiaceae) is one of the most important non-edible oilseed crops and its seed oil is broadly used for industrial applications. We performed a comprehensive genome-wide identification and analysis of the bZIP transcription factors that exist in the castor bean genome in this study. In total, 49 RcbZIP transcription factors were identified, characterized and categorized into 11 groups (I-XI) based on their gene structure, DNA-binding sites, conserved motifs, and phylogenetic relationships. The dimerization properties of 49 RcbZIP proteins were predicted on the basis of the characteristic features in the leucine zipper. Global expression profiles of 49 RcbZIP genes among different tissues were examined using high-throughput sequencing of digital gene expression profiles, and resulted in diverse expression patterns that may provide basic information to further reveal the function of the 49 RcbZIP genes in castor bean. The results obtained from this study would provide valuable information in understanding the molecular basis of the RcbZIP transcription factor family and their potential function in regulating the growth and development, particularly in seed filling of castor bean. [ABSTRACT FROM AUTHOR]

Background: MicroRNAs (miRNAs) are endogenously encoded small RNAs that post-transcriptionally regulate gene expression and play essential roles in numerous developmental and physiological processes. Currently, little information on the transcriptome and tissue-specific expression of miRNAs is available in the model non-edible oilseed crop castor bean (Ricinus communis L.), one of the most important non-edible oilseed crops cultivated worldwide. Recent advances in sequencing technologies have allowed the identification of conserved and novel miRNAs in many plant species. Here, we used high-throughput sequencing technologies to identify and characterize the miRNAs in castor bean. Results: Five small RNA libraries were constructed for deep sequencing from root tips, leaves, developing seeds (at the initial stage, seed1; and at the fast oil accumulation stage, seed2) and endosperms in castor bean. High-throughput sequencing generated a large number of sequence reads of small RNAs in this study. In total, 86 conserved miRNAs were identified, including 63 known and 23 newly identified. Sixteen miRNA isoform variants in length were found from the conserved miRNAs of castor bean. MiRNAs displayed diverse organ-specific expression levels among five libraries. Combined with criteria for miRNA annotation and a RT-PCR approach, 72 novel miRNAs and their potential precursors were annotated and 20 miRNAs newly identified were validated. In addition, new target candidates for miRNAs newly identified in this study were proposed. Conclusions: The current study presents the first high-throughput small RNA sequencing study performed in castor bean to identify its miRNA population. It characterizes and increases the number of miRNAs and their isoforms identified in castor bean. The miRNA expression analysis provides a foundation for understanding castor bean miRNA organ-specific expression patterns. The present study offers an expanded picture of miRNAs for castor bean and other members in the family Euphorbiaceae. [ABSTRACT FROM AUTHOR]

Relatively, little is known about the genetic variation of woody trees during domestication. Castor bean (Ricinus communis L. Euphorbiaceae) is a commercially important nonedible annual oilseed crop and differs from its wild progenitors that have a perennial woody habit. Although castor bean is one of the oldest cultivated crops, its domestication origin, genomic variation, and potential targets of selection underlying domestication traits remain unknown. Here, we performed a phylogenetic analysis, which suggests that the wild accessions were distinctively separated from the cultivated accessions. Genome sequencing of three accessions (one each wild, landrace, and cultivar) showed a large number of genetic variants between wild and cultivated castor bean (ZB306 or Hale), and relatively few variants between cultivar ZB306 and Hale. Comparative genome analysis revealed many candidate genes of selection and key pathways potentially involved in the transition from a perennial woody tree to annual crop. Interestingly, among 16 oil‐related genes only three showed evidence of selection and the remainder showed low genetic variation at the population level, suggesting strong purifying selection in both the wild and domesticated gene pools. These results extend our understanding of the origin, genomic variation, and domestication, and provide a valuable resource for future gene–trait associations and castor bean breeding. [ABSTRACT FROM AUTHOR]

Heat stress is one of the most challenging environmental factors for plants, which have evolved various mechanisms to cope with it. However, the role of lipid remodeling caused by heat stress is not yet fully understood. Here, we integrated UPLC-QTOF/MS-based lipidomic and transcriptomic analyzes to uncover the molecular basis of lipid remodeling under heat stress in castor bean (Ricinus communis), an important non-edible oil crop. We detected 297 lipid compounds in castor bean seedlings, of which 54 displayed altered abundances under heat stress. In particular, polyunsaturated triacylglycerols (TAGs) (e.g., TAG54:6, TAG54:7, TAG54:8, and TAG54:9) and diacylglycerols (DAGs) (DAG36:6) significantly increased, while polyunsaturated monogalactosyldiacylglycerols (MGDGs) (MGDG34:3) markedly decreased. When heat stress was subsequently relieved, these lipid molecules recovered to their normal levels. We found that heat-induced TAGs primarily accumulate in the cytosol. Transcriptomic analysis indicated that polyunsaturated fatty acids (FAs) used for TAGs are not derived from de novo synthesis, but likely from the lipids remodeling via lipase activity, and are subsequently esterified into TAGs via diacylglycerol acyltransferase (DGAT). Our results suggest that TAGs may act as intermediates in lipid turnover and provide one mechanism by which plants respond to heat stress, broadening our understanding of how lipid remodeling functions in plant adaptation to heat stress. • Lipidomics analysis reveals that polyunsaturated triacylglycerols accumulate in castor bean seedlings under heat stress. • Triacylglycerols function as an intermediate in lipid turnover and accumulate predominantly in the cytosol. • Heat induces a decrease in polyunsaturated FAs in the chloroplast lipids MGDG and DGDG. [ABSTRACT FROM AUTHOR]

• The genetic variations of the wild and cultivated castor bean were demonstrated. • Chloroplast genomes are conserved with potential DNA barcoding regions. • Several non-synonymous mutations in conserved protein domains were identified. • Cultivars could be derived from multiple wild progenitors. The high usage of castor oil in industrial applications and bio-diesel production has led to an increase in castor bean (Ricinus communis L.) cultivation in many countries. Wild species present a source of genetic variation for germplasm improvement, often important because of their adaptation to a wide range of habitats and stresses. Chloroplast genomes are widely used in population genetics and evolutionary studies. Herein, we carried out plastome genome sequencing of 20 wild and cultivated castor bean accessions to examine plastome structural variations (PSVs). Further, single nucleotide polymorphisms (SNPs) and insertions and deletions (InDels), were identified and plastome sequences used to infer phylogenetic relationships. All the chloroplast genomes were quadripartite, with a length between 162,673 bp and 163,210 bp, with 112 genes (78 protein coding genes; PCGs, 30 tRNAs, and four rRNAs). The chloroplast genomes where conserved in terms of structure and content, with no significant PSVs detected except for a slight inverted repeat (IR) contraction in one accession. A total of 162 SNPs and 92 InDels were uncovered across the plastomes, with an average SNP and InDel density of 0.99 and 0.56 per kb respectively. Some of the non-synonymous mutations caused amino acid changes in functional domains. Intergenic spacers trnE-UUC-trnT-GGU and AccD-psaI were identified as potential barcoding regions. The phylogenetic analyses and neighbor-joining network supported three distinct lineages in castor bean. Genetic diversity was greater in one clade than the other, with implications for identifying adaptive germplasm in the wild. These results demonstrate the genetic variations and phylogenetic relationships between the wild and cultivated lineages and add insights into the origin of cultivation and spread of castor bean. [ABSTRACT FROM AUTHOR]