Identification of Small RNAs During High Light Acclimation in Arabidopsis thaliana

Identification and characterization of DICER-LIKE genes and their roles in Marchantia polymorpha development and salt stress response

DICER-LIKE (DCL) proteins play a central role in plant small RNA (sRNA) biogenesis. The genome of the early land plant Marchantia polymorpha encodes four DCL proteins: MpDCL1a, MpDCL1b, MpDCL3, and MpDCL4. While MpDCL1a, MpDCL3 and MpDCL4 show high similarities to their orthologs in Physcomitrium patens and Arabidopsis thaliana, MpDCL1b shares only a limited homology with PpDCL1b, but it is very similar, in terms of functional domains, to orthologs in other moss and fern species. We generated Mpdclge mutant lines for all MpDCL genes with the CRISPR/Cas9 system and conducted phenotypic analyses under control, salt stress, and phytohormone treatments to uncover specific MpDCL functions. The mutants displayed severe developmental aberrations, altered responses to salt and phytohormones, and disturbed sexual organ development. By combining mRNA and sRNA analyses, we demonstrate that MpDCLs and their associated sRNAs play pivotal roles in regulating development, abiotic stress tolerance and phytohormone response in M. polymorpha. We identified MpDCL1a in microRNA biogenesis, MpDCL4 in trans-acting small interfering RNA generation, and MpDCL3 in the regulation of pathogen-related genes. Notably, salt sensitivity in M. polymorpha is dependent on MpDCL1b and Mpdcl1bge mutants display enhanced tolerance and reduced miRNA expression in response to salt stress. We propose that M. polymorpha employs specific mechanisms for regulating MpDCL1b associated miRNAs under high salinity conditions, potentially shared with other species harboring MpDCL1b homologs.

Cross-species transcriptomics reveals differential regulation of essential photosynthesis genes in Hirschfeldia incana

Photosynthesis is the only yield-related trait not yet substantially improved by plant breeding. Previously, we have established H. incana as the model plant for high photosynthetic light-use efficiency (LUE). Now we aim to unravel the genetic basis of this trait in H. incana, potentially contributing to the improvement of photosynthetic LUE in other species. Here, we compare its transcriptomic response to high light with that of Arabidopsis thaliana, Brassica rapa, and Brassica nigra, 3 fellow Brassicaceae members with lower photosynthetic LUE. We built a high-light, high-uniformity growing environment, in which the plants developed normally without signs of stress. We compared gene expression in contrasting light conditions across species, utilizing a panproteome to identify orthologous proteins. In-depth analysis of 3 key photosynthetic pathways showed a general trend of lower gene expression under high-light conditions for all 4 species. However, several photosynthesis-related genes in H. incana break this trend. We observed cases of constitutive higher expression (like antenna protein LHCB8), treatment-dependent differential expression (as for PSBE), and cumulative higher expression through simultaneous expression of multiple gene copies (like LHCA6). Thus, H. incana shows differential regulation of essential photosynthesis genes, with the light-harvesting complex as the first point of deviation. The effect of these expression differences on protein abundance and turnover, and ultimately the high photosynthetic LUE phenotype is relevant for further investigation. Furthermore, this transcriptomic resource of plants fully grown under, rather than briefly exposed to, a very high irradiance, will support the development of highly efficient photosynthesis in crops.

The centrality of redox regulation and sensing of reactive oxygen species in abiotic and biotic stress acclimatization

During land plant evolution, the number of genes encoding for components of the thiol redox regulatory network and the generator systems of reactive oxygen species (ROS) expanded, tentatively indicating that they have a role in tailored environmental acclimatization. This hypothesis has been validated both experimentally and theoretically during the last few decades. Recent developments of dynamic redox-sensitive GFP (roGFP)-based in vivo sensors for H2O2 and the redox potential of the glutathione pool have paved the way for dissecting the kinetics changes that occur in these crucial parameters in response to environmental stressors. The versatile cellular redox sensory and response regulatory system monitors alterations in redox metabolism and controls the activity of redox target proteins, and thereby affects most, if not all, cellular processes ranging from transcription to translation and metabolism. This review uses examples to describe the role of the redox- and ROS-dependent regulatory network in realising the appropriate responses to diverse environmental stresses. The selected case studies concern different environmental challenges, namely excess excitation energy, the heavy metal cadmium and the metalloid arsenic, nitrogen or phosphate shortages as examples for nutrient deficiency, wounding, and nematode infestation. Each challenge affects the redox-regulatory and ROS network, but our present state of knowledge also points toward pressing questions that remain open in relation to the translation of redox regulation to environmental acclimatization.

Genome-Wide Identification and Expression Analysis of the Casparian Strip Membrane Domain Protein-like Gene Family in Peanut (Arachis hypogea L.) Revealed Its Crucial Role in Growth and Multiple Stress Tolerance

Casparian strip membrane domain proteins (CASPs), regulating the formation of Casparian strips in plants, serve crucial functions in facilitating plant growth, development, and resilience to abiotic stress. However, little research has focused on the characteristics and functions of AhCASPs in cultivated peanuts. In this study, the genome-wide identification and expression analysis of the AhCASPs gene family was performed using bioinformatics and transcriptome data. Results showed that a total of 80 AhCASPs members on 20 chromosomes were identified and divided into three subclusters, which mainly localized to the cell membrane. Ka/Ks analysis revealed that most of the genes underwent purifying selection. Analysis of cis elements suggested the possible involvement of AhCASPs in hormonal and stress responses, including GA, MeJA, IAA, ABA, drought, and low temperature. Moreover, 20 different miRNAs for 37 different AhCASPs genes were identified by the psRNATarget service. Likewise, transcriptional analysis revealed key AhCASPs responding to various stresses, hormonal processing, and tissue types, including 33 genes in low temperature and drought stress and 41 genes in tissue-specific expression. These results provide an important theoretical basis for the functions of AhCASPs in growth, development, and multiple stress resistance in cultivated peanuts.

The translocase of the inner mitochondrial membrane 22-2 is required for mitochondrial membrane function during Arabidopsis seed development

The carrier translocase (also known as translocase of the inner membrane 22; TIM22 complex) is an important component of the mitochondrial protein import apparatus. However, the biological functions of AtTIM22-2 in Arabidopsis remain poorly defined. Here, we report studies on two tim22-2 mutants that exhibit defects in embryo and endosperm development, leading to seed abortion. AtTIM22-2, which was localized in mitochondria, was widely expressed in embryos and in various seedling organs. Loss of AtTIM22-2 function resulted in irregular mitochondrial cristae, decreased respiratory activity, and a lower membrane potential, together with changes in gene expression and enzyme activity related to reactive oxygen species (ROS) metabolism, leading to increased accumulation of ROS in the embryo. The levels of transcripts encoding mitochondrial protein import components were also altered in the tim22-2 mutants. Furthermore, mass spectrometry, bimolecular fluorescence complementation and co-immunoprecipitation assays revealed that AtTIM22-2 interacted with AtTIM23-2, AtB14.7 (a member of Arabidopsis OEP16 family encoded by At2G42210), and AT5G27395 (mitochondrial inner membrane translocase complex, subunit TIM44-related protein). Taken together, these results demonstrate that AtTIM22-2 is essential for maintaining mitochondrial membrane functions during seed development. These findings lay the foundations for a new model of the composition and functions of the TIM22 complex in higher plants.

miRNAs for crop improvement

Climate change significantly impacts crop production by inducing several abiotic and biotic stresses. The increasing world population, and their food and industrial demands require focused efforts to improve crop plants to ensure sustainable food production. Among various modern biotechnological tools, microRNAs (miRNAs) are one of the fascinating tools available for crop improvement. miRNAs belong to a class of small non-coding RNAs playing crucial roles in numerous biological processes. miRNAs regulate gene expression by post-transcriptional target mRNA degradation or by translation repression. Plant miRNAs have essential roles in plant development and various biotic and abiotic stress tolerance. In this review, we provide propelling evidence from previous studies conducted around miRNAs and provide a one-stop review of progress made for breeding stress-smart future crop plants. Specifically, we provide a summary of reported miRNAs and their target genes for improvement of plant growth and development, and abiotic and biotic stress tolerance. We also highlight miRNA-mediated engineering for crop improvement and sequence-based technologies available for the identification of miRNAs associated with stress tolerance and plant developmental events.

Light-Dependent Regulatory Interactions between the Redox System and miRNAs and Their Biochemical and Physiological Effects in Plants

Light intensity and spectrum play a major role in the regulation of the growth, development, and stress response of plants. Changes in the light conditions affect the formation of reactive oxygen species, the activity of the antioxidants, and, consequently, the redox environment in the plant tissues. Many metabolic processes, thus the biogenesis and function of miRNAs, are redox-responsive. The miRNAs, in turn, can modulate various components of the redox system, and this process is also associated with the alteration in the intensity and spectrum of the light. In this review, we would like to summarise the possible regulatory mechanisms by which the alterations in the light conditions can influence miRNAs in a redox-dependent manner. Daily and seasonal fluctuations in the intensity and spectral composition of the light can affect the expression of miRNAs, which can fine-tune the various physiological and biochemical processes due to their effect on their target genes. The interactions between the redox system and miRNAs may be modulated by light conditions, and the proposed function of this regulatory network and its effect on the various biochemical and physiological processes will be introduced in plants.

Role of plant microRNAs and their corresponding pathways in fluctuating light conditions

In recent years, it has been established that microRNAs (miRNAs) are critical for various plant physiological regulations in numerous species. Next-generation sequencing technologies have aided to our understandings related to the critical role of miRNAs during environmental stress conditions and plant development. Light influences not just miRNA accumulation but also their biological activities via regulating miRNA gene transcription, biosynthesis, and RNA-induced silencing complex (RISC) activity. Light-regulated routes, processes, and activities can all be affected by miRNAs. Here, we will explore how light affects miRNA gene expression and how conserved and novel miRNAs exhibit altered expression across different plant species in response to variable light quality. Here, we will mainly discuss recent advances in understanding how miRNAs are involved in photomorphogenesis, and photoperiod-dependent plant biological processes such as cell proliferation, metabolism, chlorophyll pigment synthesis and axillary bud growth. The review concludes by presenting future prospects via hoping that light-responsive miRNAs can be exploited in a better way to engineer economically important crops to ensure future food security.

Antisense Transcription in Plants: A Systematic Review and an Update on cis-NATs of Sugarcane

Initially, natural antisense transcripts (NATs, natRNAs, or asRNAs) were considered repressors; however, their functions in gene regulation are diverse. Positive, negative, or neutral correlations to the cognate gene expression have been noted. Although the first studies were published about 50 years ago, there is still much to be investigated regarding antisense transcripts in plants. A systematic review of scientific publications available in the Web of Science databases was conducted to contextualize how the studying of antisense transcripts has been addressed. Studies were classified considering three categories: “Natural antisense” (208), artificial antisense used in “Genetic Engineering” (797), or “Natural antisense and Genetic Engineering”-related publications (96). A similar string was used for a systematic search in the NCBI Gene database. Of the 1132 antisense sequences found for plants, only 0.8% were cited in PubMed and had antisense information confirmed. This value was the lowest when compared to fungi (2.9%), bacteria (2.3%), and mice (54.1%). Finally, we present an update for the cis-NATs identified in Saccharum spp. Of the 1413 antisense transcripts found in different experiments, 25 showed concordant expressions, 22 were discordant, 1264 did not correlate with the cognate genes, and 102 presented variable results depending on the experiment.

Role of phasiRNAs in plant-pathogen interactions: molecular perspectives and bioinformatics tools

The genome of an organism is regulated in concert with the organized action of various genetic regulators at different hierarchical levels. Small non-coding RNAs are one of these regulators, among which microRNAs (miRNAs), a distinguished sRNA group with decisive functions in the development, growth and stress-responsive activities of both plants as well as animals, are keenly explored over a good number of years. Recent studies in plants revealed that apart from the silencing activity exhibited by miRNAs on their targets, miRNAs of specific size and structural features can direct the phasing pattern of their target loci to form phased secondary small interfering RNAs (phasiRNAs). These trigger-miRNAs were identified to target both coding and long non-coding RNAs that act as potent phasiRNA precursors or PHAS loci. The phasiRNAs produced thereby exhibit a role in enhancing further downstream regulation either on their own precursors or on those transcripts that are distinct from their genetic source of origin. Hence, these tiny regulators can stimulate an elaborative cascade of interacting RNA networks via cis and trans-regulatory mechanisms. Our review focuses on the comprehensive understanding of phasiRNAs and their trigger miRNAs, by giving much emphasis on their role in the regulation of plant defense responses, together with a summary of the computational tools available for the prediction of the same.

Integrated Degradome and Srna Sequencing Revealed miRNA-mRNA Regulatory Networks between the Phloem and Developing Xylem of Poplar

Lignin and cellulose are the most abundant natural organic polymers in nature. MiRNAs are a class of regulatory RNAs discovered in mammals, plants, viruses, and bacteria. Studies have shown that miRNAs play a role in lignin and cellulose biosynthesis by targeting key enzymes. However, the specific miRNAs functioning in the phloem and developing xylem of Populus deltoides are still unknown. In this study, a total of 134 miRNAs were identified via high-throughput small RNA sequencing, including 132 known and two novel miRNAs, six of which were only expressed in the phloem. A total of 58 differentially expressed miRNAs (DEmiRNAs) were identified between the developing xylem and the phloem. Among these miRNAs, 21 were significantly upregulated in the developing xylem in contrast to the phloem and 37 were significantly downregulated. A total of 2431 target genes of 134 miRNAs were obtained via high-throughput degradome sequencing. Most target genes of these miRNAs were transcription factors, including AP2, ARF, bHLH, bZIP, GRAS, GRF, MYB, NAC, TCP, and WRKY genes. Furthermore, 13 and nine miRNAs were involved in lignin and cellulose biosynthesis, respectively, and we validated the miRNAs via qRT-PCR. Our study explores these miRNAs and their regulatory networks in the phloem and developing xylem of P.deltoides and provides new insight into wood formation.

Plastid retrograde regulation of miRNA expression in response to light stress

BACKGROUND

MicroRNAs (miRNAs) are a class of endogenous noncoding RNAs that play a pivotal role in the regulation of plant development and responses to the surrounding environment. Despite the efforts made to elucidate their function in the adaptation of plants to many abiotic and biotic stresses, their role in high light (HL) stress is still vague. HL stress often arises upon plant exposure to full sunlight. Subsequent changes in nuclear gene expression are triggered by chloroplast-derived retrograde signals.

RESULTS

In this study, we show that HL is involved in miRNA-dependent regulation in Arabidopsis thaliana rosettes. Microtranscriptomic screening revealed a limited number of miRNAs reacting to HL. To explain the miRNA regulation mechanisms at the different biogenesis stages, chemical and genetic approaches were applied. First, we tested the possible role of plastoquinone (PQ) redox changes using photosynthetic electron transport chain inhibitors. The results suggest that increased primary transcript abundance (pri-miRNAs) of HL-regulated miRNAs is dependent on signals upstream of PQ. This indicates that such signals may originate from photosystem II, which is the main singlet oxygen (¹O₂) source. Nevertheless, no changes in pri-miRNA expression upon a dark-light shift in the conditional fluorescent (flu) mutant producing ¹O₂ were observed when compared to wild-type plants. Thus, we explored the ¹O₂ signaling pathway, which is initiated independently in HL and is related to β-carotene oxidation and production of volatile derivatives, such as β-cyclocitral (β-CC). Pri-miRNA induction by β-CC, which is a component of this ¹O₂ pathway, as well as an altered response in the methylene blue sensitivity 1 (mbs1) mutant support the role of ¹O₂ signaling in miRNA regulation.

CONCLUSIONS

We show that light stress triggers changes in miRNA expression. This stress response may be regulated by reactive oxygen species (ROS)-related signaling. In conclusion, our results link ROS action to miRNA biogenesis, suggesting its contribution to inconsistent pri- and mature miRNA dynamics.

The Identification of MATE Antisense Transcripts in Soybean Using Strand-Specific RNA-Seq Datasets

Natural antisense transcripts (NATs) have been generally reported as negative regulators of their sense counterparts. Multidrug and toxic compound extrusion (MATE) proteins mediate the transport of various substrates. Although MATEs have been identified genome-wide in various plant species, their transcript regulators remain unclear. Here, using the publicly available strand-specific RNA-seq datasets of Glycine soja (wild soybean) which have the data from various tissues including developing pods, developing seeds, embryos, cotyledons and hypocotyls, roots, apical buds, stems, and flowers, we identified 35 antisense transcripts of MATEs from 28 gene loci after transcriptome assembly. Spearman correlation coefficients suggested the positive expression correlations of eight MATE antisense and sense transcript pairs. By aligning the identified transcripts with the reference genome of Glycine max (cultivated soybean), the MATE antisense and sense transcript pairs were identified. Using soybean C08 (Glycine max), in developing pods and seeds, the positive correlations between MATE antisense and sense transcript pairs were shown by RT-qPCR. These findings suggest that soybean antisense transcripts are not necessarily negative transcription regulators of their sense counterparts. This study enhances the existing knowledge on the transcription regulation of MATE transporters by uncovering the previously unknown MATE antisense transcripts and their potential synergetic effects on sense transcripts.