Gypsy retrotransposon-derived maize lncRNA GARR2 modulates gibberellin response

A long noncoding RNA functions in pumpkin fruit development through S-adenosyl-L-methionine synthetase

Long noncoding RNAs (lncRNAs) play important roles in various biological processes. However, the regulatory roles of lncRNAs underlying fruit development have not been extensively studied. The pumpkin (Cucurbita spp.) is a preferred model for understanding the molecular mechanisms regulating fruit development because of its variable shape and size and large inferior ovary. Here, we performed strand-specific transcriptome sequencing on pumpkin (Cucurbita maxima "Rimu") fruits at 6 developmental stages and identified 5,425 reliably expressed lncRNAs. Among the 332 lncRNAs that were differentially expressed during fruit development, the lncRNA MSTRG.44863.1 was identified as a negative regulator of pumpkin fruit development. MSTRG.44863.1 showed a relatively high expression level and an obvious period-specific expression pattern. Transient overexpression and silencing of MSTRG.44863.1 significantly increased and decreased the content of 1-aminocyclopropane carboxylic acid (a precursor of ethylene) and ethylene production, respectively. RNA pull-down and microscale thermophoresis assays further revealed that MSTRG.44863.1 can interact with S-adenosyl-L-methionine synthetase (SAMS), an enzyme in the ethylene synthesis pathway. Considering that ethylene negatively regulates fruit development, these results indicate that MSTRG.44863.1 plays an important role in the regulation of pumpkin fruit development, possibly through interacting with SAMS and affecting ethylene synthesis. Overall, our findings provide a rich resource for further study of fruit-related lncRNAs while offering insights into the regulation of fruit development in plants.

Update on functional analysis of long non-coding RNAs in common crops

With the rapid advances in next-generation sequencing technology, numerous non-protein-coding transcripts have been identified, including long noncoding RNAs (lncRNAs), which are functional RNAs comprising more than 200 nucleotides. Although lncRNA-mediated regulatory processes have been extensively investigated in animals, there has been considerably less research on plant lncRNAs. Nevertheless, multiple studies on major crops showed lncRNAs are involved in crucial processes, including growth and development, reproduction, and stress responses. This review summarizes the progress in the research on lncRNA roles in several major crops, presents key strategies for exploring lncRNAs in crops, and discusses current challenges and future prospects. The insights provided in this review will enhance our comprehension of lncRNA functions in crops, with potential implications for improving crop genetics and breeding.

Integrative transcriptome analysis uncovers common components containing CPS2 regulated by maize lncRNA GARR2 in gibberellin response

MAIN CONCLUSION

The combined transcriptome outcome provides an important clue to the regulatory cascade centering on lncRNA GARR2 and CPS2 gene in GA response. Long non-coding RNAs (lncRNAs) serve as regulatory components in transcriptional hierarchy governing multiple aspects of biological processes. Dissecting regulatory mechanisms underpinning tetracyclic diterpenoid gibberellin (GA) cascade holds both theoretical and applied significance. However, roles of lncRNAs in transcriptional modulation of GA pathway remain largely elusive. Gypsy retrotransposon-derived GIBBERELLIN RESPONSIVE lncRNA2 (GARR2) has been reported as GA-responsive maize lncRNA. Here a novel GARR2-edited line garr2-1 was identified, characteristic of GA-induced phenotype of increased seedling height and elongated leaf sheath. Transcriptome analysis indicated that transcriptional abundance of five genes [ent-copalyl diphosphate synthase2 (CPS2), ent-kaurene synthase4 (KS4), ent-kaurene synthase6 (KS6), ent-kaurene oxidase2 (KO2), and ent-kaurenoic acid oxidase1/Dwarf3 (KAO1/D3)] was elevated in garr2-1 for early steps of GA biosynthesis. Five GA biosynthetic genes as hub regulators were interlaced to shape regulatory network of GA response. Different transcriptome resources were integrated to discover common differentially expressed genes (DEGs) in the independent GARR2-edited lines GARR2KO and garr2-1. A total of 320 common DEGs were retrieved. These common DEGs were enriched in diterpenoid biosynthetic pathway. Integrative transcriptome analysis revealed the common CPS2 encoding the CPS enzyme that catalyzes the conversion of the precursor trans-geranylgeranyl diphosphate to ent-copalyl diphosphate. The up-regulated CPS2 supported the GA-induced phenotype of slender seedlings observed in the independent GARR2-edited lines GARR2KO and garr2-1. Our integrative transcriptome analysis uncovers common components of the GA pathway regulated by lncRNA GARR2. These common components, especially for the GA biosynthetic gene CPS2, provide a valuable resource for further delineating the underlying mechanisms of lncRNA GARR2 in GA response.

The long noncoding RNAs lnc10 and lnc11 regulating flavonoid biosynthesis in Ginkgo biloba

Although long non-coding RNAs have been recognized to play important roles in plant, their possible functions and potential mechanism in Ginkgo biloba flavonoid biosynthesis are poorly understood. Flavonoids are important secondary metabolites and healthy components of Ginkgo biloba. They have been widely used in food, medicine, and natural health products. Most previous studies have focused on the molecular mechanisms of structural genes and transcription factors that regulate flavonoid biosynthesis. Few reports have examined the biological functions of flavonoid biosynthesis by long non-coding RNAs in G. biloba. Long noncoding RNAs associated with flavonoid biosynthesis in G. biloba have been identified through RNA sequencing, but the function of lncRNAs has not been reported. In this study, the expression levels of lnc10 and lnc11 were identified. Quantitative real-time polymerase chain reaction analysis revealed that lnc10 and lnc11 were expressed in all detected organs, and they showed significantly higher levels in immature and mature leaves than in other organs. In addition, to fully identify the function of lnc10 and lnc11 in flavonoid biosynthesis in G. biloba, lnc10 and lnc11 were cloned from G. biloba, and were transformed into Arabidopsis and overexpressed. Compared with the wild type, the flavonoid content was increased in transgenic plants. Moreover, the RNA-sequencing analysis of wild-type, lnc10-overexpression, and lnc11-overexpression plants screened out 2019 and 2552 differentially expressed genes, and the transcript levels of structural genes and transcription factors associated with flavonoid biosynthesis were higher in transgenic Arabidopsis than in the wild type, indicating that lnc10 and lnc11 activated flavonoid biosynthesis in the transgenic lines. Overall, these results suggest that lnc10 and lnc11 positively regulate flavonoid biosynthesis in G. biloba.

CRISPR/Cas9-mediated genome editing techniques and new breeding strategies in cereals - current status, improvements, and perspectives

Cereal crops, including triticeae species (barley, wheat, rye), as well as edible cereals (wheat, corn, rice, oat, rye, sorghum), are significant suppliers for human consumption, livestock feed, and breweries. Over the past half-century, modern varieties of cereal crops with increased yields have contributed to global food security. However, presently cultivated elite crop varieties were developed mainly for optimal environmental conditions. Thus, it has become evident that taking into account the ongoing climate changes, currently a priority should be given to developing new stress-tolerant cereal cultivars. It is necessary to enhance the accuracy of methods and time required to generate new cereal cultivars with the desired features to adapt to climate change and keep up with the world population expansion. The CRISPR/Cas9 system has been developed as a powerful and versatile genome editing tool to achieve desirable traits, such as developing high-yielding, stress-tolerant, and disease-resistant transgene-free lines in major cereals. Despite recent advances, the CRISPR/Cas9 application in cereals faces several challenges, including a significant amount of time required to develop transgene-free lines, laboriousness, and a limited number of genotypes that may be used for the transformation and in vitro regeneration. Additionally, developing elite lines through genome editing has been restricted in many countries, especially Europe and New Zealand, due to a lack of flexibility in GMO regulations. This review provides a comprehensive update to researchers interested in improving cereals using gene-editing technologies, such as CRISPR/Cas9. We will review some critical and recent studies on crop improvements and their contributing factors to superior cereals through gene-editing technologies.

Important Factors Controlling Gibberellin Homeostasis in Plant Height Regulation

Plant height is an important agronomic trait that is closely associated with crop yield and quality. Gibberellins (GAs), a class of highly efficient plant growth regulators, play key roles in regulating plant height. Increasing reports indicate that transcriptional regulation is a major point of regulation of the GA pathways. Although substantial knowledge has been gained regarding GA biosynthetic and signaling pathways, important factors contributing to the regulatory mechanisms homeostatically controlling GA levels remain to be elucidated. Here, we provide an overview of current knowledge regarding the regulatory network involving transcription factors, noncoding RNAs, and histone modifications involved in GA pathways. We also discuss the mechanisms of interaction between GAs and other hormones in plant height development. Finally, future directions for applying knowledge of the GA hormone in crop breeding are described.

Plant long non-coding RNAs: identification and analysis to unveil their physiological functions

Eukaryotic genomes encode thousands of RNA molecules; however, only a minimal fraction is translated into proteins. Among the non-coding elements, long non-coding RNAs (lncRNAs) play important roles in diverse biological processes. LncRNAs are associated mainly with the regulation of the expression of the genome; nonetheless, their study has just scratched the surface. This is somewhat due to the lack of widespread conservation at the sequence level, in addition to their relatively low and highly tissue-specific expression patterns, which makes their exploration challenging, especially in plant genomes where only a few of these molecules have been described completely. Recently published high-quality genomes of crop plants, along with new computational tools, are considered promising resources for studying these molecules in plants. This review briefly summarizes the characteristics of plant lncRNAs, their presence and conservation, the different protocols to find these elements, and the limitations of these protocols. Likewise, it describes their roles in different plant physiological phenomena. We believe that the study of lncRNAs can help to design strategies to reduce the negative effect of biotic and abiotic stresses on the yield of crop plants and, in the future, help create fruits and vegetables with improved nutritional content, higher amounts of compounds with positive effects on human health, better organoleptic characteristics, and fruits with a longer postharvest shelf life.

Gene editing of non-coding regulatory DNA and its application in crop improvement

The development of the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein (CRISPR/Cas) system has provided precise and efficient strategies to edit target genes and generate transgene-free crops. Significant progress has been made in the editing of protein-coding genes; however, studies on the editing of non-coding DNA with regulatory roles lags far behind. Non-coding regulatory DNAs, including those which can be transcribed into long non-coding RNAs (lncRNAs), and miRNAs, together with cis-regulatory elements (CREs), play crucial roles in regulating plant growth and development. Therefore, the combination of CRISPR/Cas technology and non-coding regulatory DNA has great potential to generate novel alleles that affect various agronomic traits of crops, thus providing valuable genetic resources for crop breeding. Herein, we review recent advances in the roles of non-coding regulatory DNA, attempts to edit non-coding regulatory DNA for crop improvement, and potential application of novel editing tools in modulating non-coding regulatory DNA. Finally, the existing problems, possible solutions, and future applications of gene editing of non-coding regulatory DNA in modern crop breeding practice are also discussed.

Post-transcriptional and translational regulation of plant gene expression by transposons

Transposons are mobile DNA sequences that can move within the genome and integrate in new genomic locations. They are widespread in eukaryotes and prokaryotes and can influence gene expression when landing within or nearby a gene. Although transposon-induced regulation of gene expression at the transcriptional level has been extensively studied, there has been less focus on regulation at the post-transcriptional and translational levels. Recent studies in maize (Zea mays) and other plant species suggest that transposon insertions can affect RNA processing, RNA stability, protein translation and protein stability. We will describe the diverse mechanisms by which transposons can influence gene expression at the post-transcriptional and translational levels, and discuss the interactions between these mechanisms.

Deciphering shared attributes of plant long non-coding RNAs through a comparative computational approach

Over the past decade, long non-coding RNA (lncRNA), which lacks protein-coding potential, has emerged as an essential regulator of the genome. The present study examined 13,599 lncRNAs in Arabidopsis thaliana, 11,565 in Oryza sativa, and 32,397 in Zea mays for their characteristic features and explored the associated genomic and epigenomic features. We found lncRNAs were distributed throughout the chromosomes and the Helitron family of transposable elements (TEs) enriched, while the terminal inverted repeat depleted in lncRNA transcribing regions. Our analyses determined that lncRNA transcribing regions show rare or weak signals for most epigenetic marks except for H3K9me2 and cytosine methylation in all three plant species. LncRNAs showed preferential localization in the nucleus and cytoplasm; however, the distribution ratio in the cytoplasm and nucleus varies among the studied plant species. We identified several conserved endogenous target mimic sites in the lncRNAs among the studied plants. We found 233, 301, and 273 unique miRNAs, potentially targeting the lncRNAs of A. thaliana, O. sativa, and Z. mays, respectively. Our study has revealed that miRNAs, which interact with lncRNAs, target genes that are involved in a diverse array of biological and molecular processes. The miRNA-targeted lncRNAs displayed a strong affinity for several transcription factors, including ERF and BBR-BPC, mutually present in all three plants, advocating their conserved functions. Overall, the present study showed that plant lncRNAs exhibit conserved genomic and epigenomic characteristics and potentially govern the growth and development of plants.

Sugar transporter ZmSWEET1b is responsible for assimilate allocation and salt stress response in maize

Sugar efflux transporter SWEET family is involved in multiple biological processes, from nectar secretion, pollen fertility to seed filling. Although roles of SWEETs in abiotic stress adaption have been revealed mainly in reference organism Arabidopsis, cereal crops SWEETs responses to abiotic stimulation remain largely elusive. Here, we report the characterization of maize SWEET family member ZmSWEET1b, with emphasis on its response to salinity stress. ZmSWEET1b is a canonical sugar transporter, characteristic of seven transmembrane helices and plasma membrane localization. ZmSWEET1b and its rice ortholog OsSWEET1b in phylogenetic clade I underwent convergent selection during evolution. Two independent knockout lines were created by the CRISPR/Cas9 method to functionally characterized ZmSWEET1b. Sucrose and fructose contents are significantly decreased in ZmSWEET1b knockout lines. Mature leaves of ZmSWEET1b-edited lines exhibit chlorosis, reminiscent of senescence-like phenotype. Ears and seeds of ZmSWEET1b knockout lines are small. Upon salinity treatment, ZmSWEET1b-edited lines become more wilted. Transcriptional abundance of genes for Na⁺ efflux from roots to the rhizosphere, including ZmSOS1, ZmH⁺-ATPASE 2, and ZmH⁺-ATPASE 8, is decreased in salt-treated ZmSWEET1b knockout lines. These findings indicate that convergently selected sugar transporter ZmSWEET1b is important for maize plant development and responses to salt stress. The manipulation of ZmSWEET1b may represent a feasible way forward in the breeding of salinity tolerant ideotypes through the optimization of assimilate allocation.

Genome-wide identification and characterization of lncRNAs in sunflower endosperm

BACKGROUND

Long non-coding RNAs (lncRNAs), as important regulators, play important roles in plant growth and development. The expression and epigenetic regulation of lncRNAs remain uncharacterized generally in plant seeds, especially in the transient endosperm of the dicotyledons.

RESULTS

In this study, we identified 11,840 candidate lncRNAs in 12 day-after-pollination sunflower endosperm by analyzing RNA-seq data. These lncRNAs were evenly distributed in all chromosomes and had specific features that were distinct from mRNAs including tissue-specificity expression, shorter and fewer exons. By GO analysis of protein coding genes showing strong correlation with the lncRNAs, we revealed that these lncRNAs potential function in many biological processes of seed development. Additionally, genome-wide DNA methylation analyses revealed that the level of DNA methylation at the transcription start sites was negatively correlated with gene expression levels in lncRNAs. Finally, 36 imprinted lncRNAs were identified including 32 maternally expressed lncRNAs and four paternally expressed lncRNAs. In CG and CHG context, DNA methylation levels of imprinted lncRNAs in the upstream and gene body regions were slightly lower in the endosperm than that in embryo tissues, which indicated that the maternal demethylation potentially induce the paternally bias expression of imprinted lncRNAs in sunflower endosperm.

CONCLUSION

Our findings not only identified and characterized lncRNAs on a genome-wide scale in the development of sunflower endosperm, but also provide novel insights into the parental effects and epigenetic regulation of lncRNAs in dicotyledonous seeds.

Harnessing hormone gibberellin knowledge for plant height regulation

Harnessing hormone GA knowledge is a potential means to develop plant height ideotypes. Plant height holds significance for natural beauty and agricultural revolution. The increased grain productivity during the Green Revolution of the 1960s is partly attributed to the reshaping of plant stature, which is conferred by changes in phytohormone gibberellin (GA) metabolism or signaling. GA fine-tunes multiple aspects of biological events and plays a pivotal role in plant height determinant. Harnessing hormone GA knowledge is a potential means to develop ideal plant height to meet the future demand. Here, we present an overview of characterized GA pathway genes for plant height regulation. Novel alleles of Green Revolution genes sd1 and Rht are specially delineated. Through interactome analysis, we uncover GA20ox and GA3ox family members as central hub modulators of GA pathway. Empowered by GA knowledge, we suggest ways towards design breeding of plant height ideotypes through harnessing the alterations of GA cascade. We highlight the utility of genome editing to generate weak alleles to circumvent side effects of GA pathway perturbation.