Post-transcriptional control of GRF transcription factors by microRNA miR396 and GIF co-activator affects leaf size and longevity

PagWRKY11 regulates leaf morphology and salt sensitivity in Populus alba×P.glandulosa

WRKY transcription factors (TFs) are key regulators of plant tissue morphogenesis, defense responses, and metabolic regulation. However, the functions for most of WRKY TFs in 84K poplar (Populus alba × P. glandulosa) in regulating leaf morphology and responding to salt stress are remain unclear. In this study, overexpressing PagWRKY11 poplars were generated. Phenotypic analysis revealed that transgenic poplar leaves were narrower and smoother compared to the traditionally elliptical and relatively rough leaves of wild-type (WT) plants. Then, the apical buds of transgenic poplars were sharp and elongated, with young leaves pointing upwards and inwards, whereas WT buds were rounder with smoother young leaves pointing downwards. Functional analysis indicated that under salt stress, the activities of SOD and POD enzymes and the expression of their encoding genes were significantly lower in transgenic poplars compared to WT. Conversely, the accumulation of H2O2 and MDA was significantly higher. These results suggest that overexpression lines of PagWRKY11 increase salt sensitivity by downregulating the expression of antioxidant enzyme genes. Meanwhile, overexpression of PagWRKY11 increased the natural water loss rate of poplar leaves, and negatively regulated salt stress by affecting water retention. In addition, yeast one-hybrid assays showed that PagWRKY11 binds specifically to W-box elements. These results provide a theoretical basis for further exploration of the molecular mechanisms by which PagWRKY11 regulates leaf morphogenesis and stress responses, and offer new potential strategies for resistance breeding.

Overexpression of SlGRF4 positively regulates drought stress tolerance in tomato by alleviating ROS damage and increasing nitrogen signaling pathway

Drought stress caused by water scarcity is a major abiotic factor limiting plant productivity in many regions worldwide. Drought stress not only affects the morphological structure and physiological process of plants, but also induces the production of a large number of reactive oxygen species (ROS) in plants. The Growth Regulation Factor (GRF) protein, a group of plant-specific transcription factors, plays a critical role in plant growth, development, and stress responses. However, the role of tomato SlGRF4 in drought stress response and its regulatory mechanism remain poorly understood. In this study, bioinformatic analysis revealed that SlGRF4 contains the conserved QLQ and WRC domains characteristic of GRF. SlGRF4 was induced by 15% PEG, especially after 3h of treatment. Under drought stress, SlGRF4-overexpressing tomato seeds exhibit longer root length and plant height, compared with wild type (WT). Overexpressing of SlGRF4 reduced ROS and malondialdehyde (MDA) contents, enhanced activities and expression of antioxidant enzyme, contents and gene expression of proline, compared to WT plants. The expression levels of nitrogen metabolism genes (SlNR, SlNIR, SlGS, SlGOGAT), as well as transcripts of nitrate transporter proteins (SlNRT1.1, SlNRT1.2, SlNRT2.1, SlNRT2.2, SlNRT2.3, SlNRT2.4), were significantly upregulated in transgenic tomato plants under drought stress. Yeast two hybrid (Y2H) and luciferase complementation assay (LCA) indicated that SlGRF4 interacted with SlGIFs. Furthermore, luciferase reporter assays, yeast one-hybrid (Y1H) assays, and electrophoretic mobility shift assays (EMSA) confirmed that SlGRF4 directly binds to the promoter of SlNRT2.2, thereby activating its expression. Our findings highlighting the potential role of SlGRF4 in regulating drought tolerance in tomato plants.

The DNA binding of plant-specific GROWTH-REGULATING FACTOR transcription factors is stabilized by GRF-INTERACTING FACTOR coactivators

The plant-specific GROWTH-REGULATING FACTOR (GRF) transcription factor family proteins play crucial role in regulating diverse aspects of plant life. The transcriptional activity of GRFs is known to be enhanced through direct interaction with the GRF-INTERACTING FACTOR (GIF) coactivators. However, it remains unclear how the binding to GIF affects the biochemical ability of GRFs. Herein, we present evidence that GIFs also stabilize the DNA binding of GRFs. A combination of biochemical experiments and AlphaFold-predicted structural models suggests that the GIF-binding domain in GRFs may partially restrict their own DNA binding through direct interaction with the DNA-binding domain in the absence of GIFs. These findings deepen our understanding of the GRF:GIF module in plant regulation and provide a basis for strategies to manipulate this module for agricultural and biotechnological applications.

Unveiling shared genetic regulators of plant architectural and biomass yield traits in the Sorghum Association Panel

Sorghum is emerging as an ideal genetic model for designing high-biomass bioenergy crops. Biomass yield, a complex trait influenced by various plant architectural characteristics, is typically regulated by numerous genes. This study aimed to dissect the genetic regulators underlying 14 plant architectural traits and 10 biomass yield traits in the Sorghum Association Panel across two growing seasons. We identified 321 associated loci through genome-wide association studies (GWAS), involving 234 264 single nucleotide polymorphisms (SNPs). These loci include genes with known associations to biomass traits, such as maturity, dwarfing (Dw), and leafbladeless1, as well as several uncharacterized loci not previously linked to these traits. We also identified 22 pleiotropic loci associated with variation in multiple phenotypes. Three of these loci, located on chromosomes 3 (S03_15463061), 6 (S06_42790178; Dw2), and 9 (S09_57005346; Dw1), exerted significant and consistent effects on multiple traits across both growing seasons. Additionally, we identified three genomic hotspots on chromosomes 6, 7, and 9, each containing multiple SNPs associated with variation in plant architecture and biomass yield traits. Chromosome-wise correlation analyses revealed multiple blocks of positively associated SNPs located near or within the same genomic regions. Finally, genome-wide correlation-based network analysis showed that loci associated with flowering, plant height, leaf traits, plant density, and tiller number per plant were highly interconnected with other genetic loci influencing plant architectural and biomass yield traits. The pyramiding of favorable alleles related to these traits holds promise for enhancing the future development of bioenergy sorghum crops.

Individual leaf microbiota tunes a genetic regulatory network to promote leaf growth

In natural ecosystems, microbes have the ability to stably colonize plant leaves, overcoming the fluctuating environmental conditions that the leaves represent. How the phyllosphere microbiota influences the growth of individual leaves remains poorly understood. Here, we investigate the growth of Zea mays (maize/corn) leaves in plants grown in three soils with differing amounts of nutrients and water and identify a leaf-growth-promoting effect driven by the leaf microbiota, which we also validate in field studies. We built and used a bacterial strain collection for recolonization experiments to study the microbiota-mediated mechanisms involved in leaf growth promotion. We demonstrate that prevalent bacteria inhabiting young leaves promote individual leaf growth. Using transcriptomic analyses, we reveal a defense-related genetic network that integrates the beneficial effect of the phyllosphere microbiota into the leaf development program. We demonstrate that the individual leaf microbiota differentially represses this genetic network to modulate the growth-defense trade-off at single-leaf resolution.

In silico genome-wide analysis of the growth-regulating factor gene family and their expression profiling in Vitis vinifera under biotic stress

Growth regulatory factors (GRFs) are transcription factors that encode the proteins involved in plant growth and development. However, no comprehensive analysis of Vitis vinifera GRF genes has yet been conducted. In the current study, we performed a genome-wide analysis of the GRF gene family to explore the VvGRF gene's role in Vitis vinifera. We identified 30 VvGRF genes in the Vitis vinifera genome, localized over 20 chromosomes. Based on evolutionary analysis, 49 GRF genes (nine AtGRF, ten FvGRF, and 30 VvGRF) were clustered into six groups. Many cis-elements involved in light control, defense, and plant growth have been identified in the promoter region of VvGRF genes, and multiple miRNAs have been predicted to be involved in regulating VvGRF gene expression. Protein-protein interaction analysis showed that nine VvGRF proteins formed a complex protein interaction network. Furthermore, the gene expression analysis of VvGRF revealed that VvGRF-5 and VvGRF-6 were highly upregulated suggesting that these genes are involved in biotic responses. This study provides comprehensive insights into the functional characteristics and occurrence of the VvGRF gene family in Vitis vinifera, which may be applied in breeding programs to enhance the growth of Vitis vinifera varieties under stress and growth changes.

Identification of the citrus GRF gene family and its expression in fruit peel thickening mediated by gibberellin

BACKGROUND

Growth-regulating factors (GRFs) play a crucial role in plant growth and development, particularly in cell division and expansion. Citrus fruit cracking, a prevalent issue, adversely impacts both yield and fruit quality. Gibberellins (GAs) are known to ameliorate citrus fruit cracking by inducing thicker peel formation, which is attributed to cell division and expansion. However, the mechanistic link between gibberellins and citrus peel thickening, and whether this process is mediated by GRF genes regulation, has not been definitively established.

RESULTS

In this study, 8 CsGRFs (Citrus sinensis), 11 CcGRFs (Citrus clementina), and 8 CgGRFs (Citrus grandis) were identified from the citrus genome which divided into six clusters, with the genes of the same cluster sharing similar gene structures. Cis-elements analysis revealed that the promoter regions of GRF genes contained numerous hormone-responsive elements. Tissue expression profiles showed that CsGRF genes had higher expression levels in young tissues, including early fruit tissues, one-year-leaf, ovules, and root tips. RNA-seq and qPCR analyses revealed that the expression levels of CsGRF3, 4, 7, and 8 were significantly regulated in response to GA3 treatment. Notably, CsGRF8 was the most significantly induced by GA3 and highly expressed in the early stages of peel development. These findings indicate gibberellins may exert regulatory effects on peel development through the induction of CsGRF genes.

CONCLUSION

This study systematically analyzed the characteristics of the citrus GRF gene family, as well as the changes in citrus peel thickness and the expression patterns of CsGRF genes under gibberellin treatment. These findings provide valuable insights for advancing research on the role of CsGRF genes in regulating citrus peel development, which could help reduce the occurrence of fruit cracking.

CLINICAL TRIAL NUMBER

Not applicable.

Division Zone Activity Determines the Potential of Drought-Stressed Maize Leaves to Resume Growth after Rehydration

Drought is one of the most devastating causes of yield losses in crops like maize, and the anticipated increases in severity and duration of drought spells due to climate change pose an imminent threat to agricultural productivity. To understand the drought response, phenotypic and molecular studies are typically performed at a given time point after drought onset, representing a steady-state adaptation response. Because growth is a dynamic process, we monitored the drought response with high temporal resolution and examined cellular and transcriptomic changes after rehydration at 4 and 6 days after leaf four appearance. These data showed that division zone activity is a determinant for full organ growth recovery upon rehydration. Moreover, a prolonged maintenance of cell division by the ectopic expression of PLASTOCHRON1 extends the ability to resume growth after rehydration. The transcriptome analysis indicated that GROWTH-REGULATING FACTORS (GRFs) affect leaf growth by impacting cell division duration, which was confirmed by a prolonged recovery potential of the GRF1-overexpression line after rehydration. Finally, we used a multiplex genome editing approach to evaluate the most promising differentially expressed genes from the transcriptome study and as such narrowed down the gene space from 40 to seven genes for future functional characterization.

Epigenetic factors related to recalcitrance in plant biotechnology

This review explores the challenges and potential solutions in plant micropropagation and biotechnology. While these techniques have proven successful for many species, certain plants or tissues are recalcitrant and do not respond as desired, limiting the application of these technologies due to unattainable or minimal in vitro regeneration rates. Indeed, traditional in vitro culture techniques may fail to induce organogenesis or somatic embryogenesis in some plants, leading to classification as in vitro recalcitrance. This paper focuses on recalcitrance to somatic embryogenesis due to its promise for regenerating juvenile propagules and applications in biotechnology. Specifically, this paper will focus on epigenetic factors that regulate recalcitrance as understanding them may help overcome these barriers. Transformation recalcitrance is also addressed, with strategies proposed to improve transformation frequency. The paper concludes with a review of CRISPR-mediated genome editing's potential in modifying somatic embryogenesis-related epigenetic status and strategies for addressing transformation recalcitrance.

Unlocking regeneration potential: harnessing morphogenic regulators and small peptides for enhanced plant engineering

Plant genetic transformation is essential for understanding gene functions and developing improved crop varieties. Traditional methods, often genotype-dependent, are limited by plants' recalcitrance to gene delivery and low regeneration capacity. To overcome these limitations, new approaches have emerged that greatly improve efficiency and genotype flexibility. This review summarizes key strategies recently developed for plant transformation, focusing on groundbreaking technologies enhancing explant- and genotype flexibility. It covers the use of morphogenic regulators (MRs), stem cell-based methods, and in planta transformation methods. MRs, such as maize Babyboom (BBM) with Wuschel2 (WUS2), and GROWTH-REGULATING FACTORs (GRFs) with their cofactors GRF-interacting factors (GIFs), offer great potential for transforming many monocot species, including major cereal crops. Optimizing BBM/WUS2 expression cassettes has further enabled successful transformation and gene editing using seedling leaves as starting material. This technology lowers the barriers for academic laboratories to adopt monocot transformation systems. For dicot plants, tissue culture-free or in planta transformation methods, with or without the use of MRs, are emerging as more genotype-flexible alternatives to traditional tissue culture-based transformation systems. Additionally, the discovery of the local wound signal peptide Regeneration Factor 1 (REF1) has been shown to enhance transformation efficiency by activating wound-induced regeneration pathways in both monocot and dicot plants. Future research may combine these advances to develop truly genotype-independent transformation methods.

Dynamic Chromatin Accessibility and Gene Expression Regulation During Maize Leaf Development

BACKGROUND/OBJECTIVES

Chromatin accessibility is closely associated with transcriptional regulation during maize (Zea mays) leaf development. However, its precise role in controlling gene expression at different developmental stages remains poorly understood. This study aimed to investigate the dynamics of chromatin accessibility and its influence on genome-wide gene expression during the BBCH_11, BBCH_13, and BBCH_17 stages of maize leaf development.

METHODS

Maize leaves were collected at the BBCH_11, BBCH_13, and BBCH_17 developmental stages, and chromatin accessibility was assessed using ATAC-seq. RNA-seq was performed to profile gene expression. Integrated analysis of ATAC-seq and RNA-seq data was conducted to elucidate the relationship between chromatin accessibility and transcriptional regulation.

RESULTS

A total of 46,808, 38,242, and 41,084 accessible chromatin regions (ACRs) were identified at the BBCH_11, BBCH_13, and BBCH_17 stages, respectively, with 23.4%, 12.2%, and 21.9% of these regions located near transcription start sites (TSSs). Integrated analyses revealed that both the number and intensity of ACRs significantly influence gene expression levels. Motif analysis identified key transcription factors associated with leaf development and potential transcriptional repressors among genes, showing divergent regulation patterns in ATAC-seq and RNA-seq datasets.

CONCLUSIONS

These findings demonstrate that chromatin accessibility plays a crucial role in regulating the spatial and temporal expression of key genes during maize leaf development by modulating transcription factor binding. This study provides novel insights into the regulatory mechanisms underlying maize leaf development, contributing to a deeper understanding of chromatin-mediated gene expression.

Genetic Foundation of Leaf Senescence: Insights from Natural and Cultivated Plant Diversity

Leaf senescence, the final stage of leaf development, is crucial for plant fitness as it enhances nutrient reutilization, supporting reproductive success and overall plant adaptation. Understanding its molecular and genetic regulation is essential to improve crop resilience and productivity, particularly in the face of global climate change. This review explores the significant contributions of natural genetic diversity to our understanding of leaf senescence, focusing on insights from model plants and major crops. We discuss the physiological and adaptive significance of senescence in plant development, environmental adaptation, and agricultural productivity. The review emphasizes the importance of natural genetic variation, including studies on natural accessions, landraces, cultivars, and artificial recombinant lines to unravel the genetic basis of senescence. Various approaches, from quantitative trait loci mapping to genome-wide association analysis and in planta functional analysis, have advanced our knowledge of senescence regulation. Current studies focusing on key regulatory genes and pathways underlying natural senescence, identified from natural or recombinant accession and cultivar populations, are highlighted. We also address the adaptive implications of abiotic and biotic stress factors triggering senescence and the genetic mechanisms underlying these responses. Finally, we discuss the challenges in translating these genetic insights into crop improvement. We propose future research directions, such as expanding studies on under-researched crops, investigating multiple stress combinations, and utilizing advanced technologies, including multiomics and gene editing, to harness natural genetic diversity for crop resilience.

Mobile signals, patterning, and positional information in root development

Multicellular organisms use mobile intercellular signals to generate spatiotemporal patterns of growth and differentiation. These signals, termed morphogens, arise from localized sources and move by diffusion or directional transport to be interpreted at target cells. The classical model for a morphogen is where a substance diffuses from a source to generate a concentration gradient that provides positional information across a field. This concept, presented by Wolpert and popularized as the "French Flag Model," remains highly influential, but other patterning models, which do not rely on morphogen gradients, also exist. Here, we review current evidence for mobile morphogenetic signals in plant root development and how they fit within existing conceptual frameworks for pattern formation. We discuss how the signals are formed, distributed, and interpreted in space and time, emphasizing the regulation of movement on the ability of morphogens to specify patterns. While significant advances have been made in the field since the first identification of mobile morphogenetic factors in plants, key questions remain to be answered, such as how morphogen movement is regulated, how these mechanisms allow scaling in different species, and how morphogens act to enable plant regeneration in response to damage.

Water wisteria genome reveals environmental adaptation and heterophylly regulation in amphibious plants

Heterophylly is a phenomenon whereby an individual plant dramatically changes leaf shape in response to the surroundings. Hygrophila difformis (Acanthaceae; water wisteria), has recently emerged as a model plant to study heterophylly because of its striking leaf shape variation in response to various environmental factors. When submerged, H. difformis often develops complex leaves, but on land it develops simple leaves. Leaf complexity is also influenced by other factors, such as light density, humidity, and temperature. Here, we sequenced and assembled the H. difformis chromosome-level genome (scaffold N50: 60.43 Mb, genome size: 871.92 Mb), which revealed 36 099 predicted protein-coding genes distributed over 15 pseudochromosomes. H. difformis diverged from its relatives during the Oligocene climate-change period and expanded gene families related to its amphibious habit. Genes related to environmental stimuli, leaf development, and other pathways were differentially expressed in submerged and terrestrial conditions, possibly modulating morphological and physiological acclimation to changing environments. We also found that auxin plays a role in H. difformis heterophylly. Finally, we discovered candidate genes that respond to different environmental conditions and elucidated the role of LATE MERISTEM IDENTITY 1 (LMI1) in heterophylly. We established H. difformis as a model for studying interconnections between environmental adaptation and morphogenesis.

Tae-miR396b regulates TaGRFs in spikes of three wheat spike mutants

Tillering and spike differentiation are key agronomic traits for wheat (Triticum aestivum L.) production. Numerous studies have shown that miR396 and growth-regulating factor genes (GRFs) are involved in growth and development of different plant organs. Previously, we have reported that wheat miR396b (tae-miR396b) and their targets TaGRFs (T. aestivum GRFs) play important roles in regulating wheat tillering. This study was to investigate the regulatory roles of tae-miR396b and TaGRFs played during wheat spike development. Wheat cultivar Guomai 301 (wild type, WT) and its three sipke mutants dwarf round spike mutant (drs), apical spikelet sterility mutant (ass) and prematurely terminated spike differentiation mutant (ptsd1) were studied. Three homeologous genes of tae-miR396b on the long arms of chromosomes 6A, 6B, and 6D were identified, and they encoded the same mature miRNA. Complementary sequences of mature tae-miR396b were identified in 23 TaGRFs, indicating they were the target genes of tae-miR396b. Tae-miR396b had different regulatory effects on TaGRFs between Guomai 301 and its mutants. TaGRF2-7A was confirmed to be the target gene of tae-miR396b by molecular interaction assay. The expression levels of tae-miR396b and TaGRFs were different between WT and mutants drs, ass and ptsd1 at the floret primordium visible (S1), the two awns/spikelet reaching apical meristem of the spikelet (S2), and the green anther stage (S3). The expression level of tae-miR396b in WT was significantly higher than that in mutants drs and ass. The most TaGRFs were negatively regulated by tae-miR396b. The abnormal expressions of TaGRF1 (6A, 6D), TaGRF2 (7A, 7B, 7D), TaGRF4 (6A, 6B), TaGRF5 (4A, 7A, 7D), and TaGRF10 (6A, 6B, 6D) were important causes for abnormal spike development in the three mutants. This study laid foundation for further elucidating functions of tae-miR396b and TaGRFs underlying wheat spike development. Regulating tae-miR396b and TaGRFs will be a new approach for wheat high yield breeding.

Overexpression of Vitis GRF4-GIF1 improves regeneration efficiency in diploid Fragaria vesca Hawaii 4

BACKGROUND

Plant breeding played a very important role in transforming strawberries from being a niche crop with a small geographical footprint into an economically important crop grown across the planet. But even modern marker assisted breeding takes a considerable amount of time, over multiple plant generations, to produce a plant with desirable traits. As a quicker alternative, plants with desirable traits can be raised through tissue culture by doing precise genetic manipulations. Overexpression of morphogenic regulators previously known for meristem development, the transcription factors Growth-Regulating Factors (GRFs) and the GRF-Interacting Factors (GIFs), provided an efficient strategy for easier regeneration and transformation in multiple crops.

RESULTS

We present here a comprehensive protocol for the diploid strawberry Fragaria vesca Hawaii 4 (strawberry) regeneration and transformation under control condition as compared to ectopic expression of different GRF4-GIF1 chimeras from different plant species. We report that ectopic expression of Vitis vinifera VvGRF4-GIF1 provides significantly higher regeneration efficiency during re-transformation over wild-type plants. On the other hand, deregulated expression of miRNA resistant version of VvGRF4-GIF1 or Triticum aestivum (wheat) TaGRF4-GIF1 resulted in abnormalities. Transcriptomic analysis between the different chimeric GRF4-GIF1 lines indicate that differential expression of FvExpansin might be responsible for the observed pleiotropic effects. Similarly, cytokinin dehydrogenase/oxygenase and cytokinin responsive response regulators also showed differential expression indicating GRF4-GIF1 pathway playing important role in controlling cytokinin homeostasis.

CONCLUSION

Our data indicate that ectopic expression of Vitis vinifera VvGRF4-GIF1 chimera can provide significant advantage over wild-type plants during strawberry regeneration without producing any pleiotropic effects seen for the miRNA resistant VvGRF4-GIF1 or TaGRF4-GIF1.

Knockout mutation in TaD27 enhances number of productive tillers in hexaploid wheat

Recent advances allow the deployment of cluster regularly interspaced short palindromic repeats (CRISPR)-associated endonucleases (Cas) system for the targeted mutagenesis in the genome with accuracy and precision for trait improvement in crops. CRISPR-Cas systems have been extensively utilized to induce knockout or frameshift mutations in the targeted sequence of mostly negative regulating genes for wheat improvement. However, most of the reported work has been done in non-commercial varieties of wheat and introgression of edited alleles into breeding population comes with the penalty of unwanted linkage-drag. Wheat yield is controlled by various genes such as positive and negative regulators. The TaD27 gene is described as a negative regulator of shoot branching or tillering and involved in the biosynthesis of strigolactones. In this study, we developed Tad27 knockout mutant lines of an elite wheat cultivar that showed a twofold increase in the number of tillers and 1.8-fold increase in the number of grains per plant. Subsequently, enhancing the grain yield without any morphological penalty in the architecture of the plants. The co-transformation of regeneration enhancing growth regulator, Growth Regulating Factor 4 (GRF4) and its cofactor GRF-Interacting Factor 1 (GIF1), under single T-DNA cassette improved the regeneration efficiency up to 6% of transgenic events from mature embryos of wheat. Our results indicate that the CRISPR-mediated targeted mutagenesis confers the potential to knockout yield-related negative regulators in elite cultivars of wheat that can substantially enhance grain yield per plant and this strategy can be harnessed for the improvement of future wheat.

A microRNA396b-growth regulating factor module controls castor seed size by mediating auxin synthesis

Castor (Ricinus communis L.) is an importance crop cultivated for its oil and economic value. Seed size is a crucial factor that determines crop yield. Gaining insight into the molecular regulatory processes of seed development is essential for the genetic enhancement and molecular breeding of castor. Here, we successfully fine-mapped a major QTL related to seed size, qSS3, to a 180 kb interval on chromosome 03 using F2 populations (DL01×WH11). A 17.6-kb structural variation (SV) was detected through genomic comparison between DL01 and WH11. Analysis of haplotypes showed that the existence of the complete 17.6 kb structural variant may lead to the small seed characteristic in castor. In addition, we found that qSS3 contains the microRNA396b (miR396b) sequence, which is situated within the 17.6 kb SV. The results of our experiment offer additional evidence that miR396-Growth Regulating Factor 4 (GRF4) controls seed size by impacting the growth and multiplication of seed coat and endosperm cells. Furthermore, we found that RcGRF4 activates the expression of YUCCA6 (YUC6), facilitating the production of IAA in seeds and thereby impacting the growth of castor seeds. Our research has discovered a crucial functional module that controls seed size, offering a fresh understanding of the mechanism underlying seed size regulation in castor.

The interplay of growth-regulating factor 5 and BZR1 in coregulating chlorophyll degradation in poplar

Chlorophyll (Chl) is essential for plants to carry out photosynthesis, growth and development processes. Growth-regulating factors (GRFs) play a vital role in regulating Chl degradation in plants. However, the molecular mechanism by which GRF5 regulates Chl degradation in poplar remains unknown. Here we found that overexpression of PpnGRF5-1 increased Chl content in leaves and promoted chloroplast development in poplar. Overexpression of PpnGRF5-1 in poplar delayed Chl degradation induced by external factors, such as hormones, darkness and salt stress. PpnGRF5-1 responded to brassinosteroid (BR) signalling during BR-induced Chl degradation and reduced the expression levels of Chl degradation and senescence-related genes. PpnGRF5-1 inhibited the expression of Chl b reductases PagNYC1 and PagNOL. PpnGRF5-1 could interact with PagBZR1 in the nucleus. PagBZR1 also inhibited the expression of PagNYC1. In addition, we found that the protein-protein interaction between PagBZR1 and PpnGRF5-1 enhanced the inhibitory effect of PpnGRF5-1 on the Chl b reductases PagNYC1 and PagNOL. BZR1 and GRF5-1 were upregulated, and NOL and NYC1 were downregulated in triploid poplars compared to diploids. This study revealed a new mechanism by which PpnGRF5-1 regulates Chl degradation in poplars and lays the foundation for comprehensively analysing the molecular mechanism of Chl metabolism in triploid poplars.

Characterization of the Arabidopsis Mutant oligocellula6-D Reveals the Importance of Leaf Initiation in Determining the Final Leaf Size

The leaf is a determinate organ with a final size under genetic control. Numerous factors that regulate the final leaf size have been identified in Arabidopsis thaliana; although most of these factors play their roles during the growth of leaf primordia, much less is known about leaf initiation and its effects on the final leaf size. In this study, we characterized oligocellula6-D (oli6-D), a semidominant mutant of A. thaliana with smaller leaves than the wild type (WT) due to its reduced leaf cell numbers. A time-course analysis showed that oli6-D had approximately 50% fewer leaf cells even immediately after leaf initiation; this difference was maintained throughout leaf development. Next-generation sequencing showed that oli6-D had chromosomal duplications involving 2-kb and 3-Mb regions of chromosomes 2 and 4, respectively. Several duplicated genes examined had approximately 2-fold higher expression levels, and at least one gene acquired a new intron/exon structure due to a chromosome fusion event. oli6-D showed reduced auxin responses in leaf primordia, primary roots and embryos, as well as reduced apical dominance and partial auxin-resistant root growth. CRISPR-associated protein-9-mediated genome editing enabled the removal of a 3-Mb duplicated segment, the largest targeted deletion in plants thus far. As a result, oli6-D restored the WT leaf phenotypes, demonstrating that oli6-D is a gain-of-function mutant. Our results suggest a new regulatory point of leaf size determination that functions at a very early stage of leaf development and is negatively regulated by one or more genes located in the duplicated chromosomal segments.

Regulation of nitrogen metabolism by COE2 under low sulfur stress in Arabidopsis

The interplay between nitrogen and sulfur assimilation synergistically supports and sustains plant growth and development, operating in tandem to ensure coordinated and optimal outcomes. Previously, we characterized Arabidopsis CHLOROPHYLL A/B-BINDING (CAB) overexpression 2 (COE2) mutant, which has a mutation in the NITRIC OXIDE-ASSOCIATED (NOA1) gene and exhibits deficiency in root growth under low nitrogen (LN) stress. This study found that the growth suppression in roots and shoots in coe2 correlates with decreased sensitivity to low sulfur stress treatment compared to the wild-type. Therefore, we examined the regulatory role of COE2 in nitrogen and sulfur interaction by assessing the expression of nitrogen metabolism-related genes in coe2 seedlings under low sulfur stress. Despite the notable upregulation of nitrate reductase genes (NIA1 and NIA2), there was a considerable reduction in nitrogen uptake and utilization, resulting in a substantial growth penalty. Moreover, the elevated expression of miR396 perhaps complemented growth stunting by selectively targeting and curtailing the expression levels of GROWTH REGULATING FACTOR 2 (GRF2), GRF4, and GRF9. This study underscores the vital role of COE2-mediated nitrogen signaling in facilitating seedling growth under sulfur deficiency stress.

Decoding the functionality of plant transcription factors

Transcription factors (TFs) intricately govern cellular processes and responses to external stimuli by modulating gene expression. TFs help plants to balance the trade-off between stress tolerance and growth, thus ensuring their long-term survival in challenging environments. Understanding the factors and mechanisms that define the functionality of plant TFs is of paramount importance for unravelling the intricate regulatory networks governing development, growth, and responses to environmental stimuli in plants. This review provides a comprehensive understanding of these factors and mechanisms defining the activity of TFs. Understanding the dynamic nature of TFs has practical implications for modern molecular breeding programmes, as it provides insights into how to manipulate gene expression to optimize desired traits in crops. Moreover, recent studies also report the functional duality of TFs, highlighting their ability to switch between activation and repression modes; this represents an important mechanism for attuning gene expression. Here we discuss what the possible reasons for the dual nature of TFs are and how this duality instructs the cell fate decision during development, and fine-tunes stress responses in plants, enabling them to adapt to various environmental challenges.

miRNA Sequencing Analysis in Maize Roots Treated with Neutral and Alkaline Salts

Soil salinization/alkalization is a complex environmental factor that includes not only neutral salt NaCl but also other components like Na2CO3. miRNAs, as small molecules that regulate gene expression post-transcriptionally, are involved in plant responses to abiotic stress. In this study, maize seedling roots were treated for 5 h with 100 mM NaCl, 50 mM Na2CO3, and H2O, respectively. Sequencing analysis of differentially expressed miRNAs under these conditions revealed that the Na2CO3 treatment group had the most differentially expressed miRNAs. Cluster analysis indicated their main involvement in the regulation of ion transport, binding, metabolism, and phenylpropanoid and flavonoid biosynthesis pathways. The unique differentially expressed miRNAs in the NaCl treatment group were related to the sulfur metabolism pathway. This indicates a significant difference in the response patterns of maize to different treatment groups. This study provides theoretical evidence and genetic resources for further analysis of the molecular mechanisms behind maize's salt-alkali tolerance.

ldi-miR396-LdPMaT1 enhances reactive oxygen species scavenging capacity and promotes drought tolerance in Lilium distichum Nakai autotetraploids

Drought is a key environmental stress that inhibits plant growth, development, yield and quality. Whole-genome replication is an effective method for breeding drought resistant cultivars. Here, we evaluated the tolerance of Lilium distichum Nakai diploids (2n = 2× = 24) and artificially induced autotetraploids (2n = 4× = 48) to drought simulated by polyethylene glycol (PEG) stress. Autotetraploids showed stronger drought tolerance than diploids, and high-throughput sequencing during PEG stress identified five differentially expressed miRNAs. Transcriptome analysis revealed significantly different reactive oxygen species (ROS)-scavenger expression levels between diploids and autotetraploids, which increased the drought tolerance of autotetraploids. Specifically, we identified ldi-miR396b and its only target gene (LdPMaT1) for further study based on its expression level and ROS-scavenging ability in response to drought stress (DS). Autotetraploids showed higher expression of LdPMaT1 and significantly downregulated expression of ldi-miR396b under DS compared with diploids. Through a short tandem target mimic (STTM) in transgenic lilies, functional studies revealed that miR396b silencing promotes LdPMaT1 expression and the DS response. Under PEG stress, STTM393 transgenic lines showed improved drought resistance mediated by lowered MDA content but exhibited high antioxidant enzyme activity, consistent with the autotetraploid results. Collectively, these findings suggest that ldi-miR396b-LdPMaT1 potentially enhances ROS-scavenging ability, which contributes to improved stress adaptation in autotetraploid lilies.

Genome-wide identification and expression profiling of growth‑regulating factor (GRF) and GRF‑interacting factor (GIF) gene families in chickpea and pigeonpea

The growth-regulating factor (GRF) and GRF-interacting factor (GIF) families encode plant-specific transcription factors and play vital roles in plant development and stress response processes. Although GRF and GIF genes have been identified in various plant species, there have been no reports of the analysis and identification of the GRF and GIF transcription factor families in chickpea (Cicer arietinum) and pigeonpea (Cajanus cajan). The present study identified seven CaGRFs, eleven CcGRFs, four CaGIFs, and four CcGIFs. The identified proteins were grouped into eight and three clades for GRFs and GIFs, respectively based on their phylogenetic relationships. A comprehensive in-silico analysis was performed to determine chromosomal location, sub-cellular localization, and types of regulatory elements present in the putative promoter region. Synteny analysis revealed that GRF and GIF genes showed diploid-polyploid topology in pigeonpea, but not in chickpea. Tissue-specific expression data at the vegetative and reproductive stages of the plant showed that GRFs and GIFs were strongly expressed in tissues like embryos, pods, and seeds, indicating that GRFs and GIFs play vital roles in plant growth and development. This research characterized GRF and GIF families and hints at their primary roles in the chickpea and pigeonpea growth and developmental process. Our findings provide potential gene resources and vital information on GRF and GIF gene families in chickpea and pigeonpea, which will help further understand the regulatory role of these gene families in plant growth and development.

Molecular mechanisms regulating GROWTH-REGULATING FACTORS activity in plant growth, development, and environmental responses

Plants rely on complex regulatory mechanisms to ensure proper growth and development. As plants are sessile organisms, these mechanisms must be flexible enough to adapt to changes in the environment. GROWTH-REGULATING FACTORS (GRFs) are plant-specific transcription factors that act as a central hub controlling plant growth and development, which offer promising biotechnological applications to enhance plant performance. Here, we analyze the complex molecular mechanisms that regulate GRFs activity, and how their natural and synthetic variants can impact on plant growth and development. We describe the biological roles of the GRFs and examine how they regulate gene expression and contribute to the control of organ growth and plant responses to a changing environment. This review focuses on the premise that unlocking the full biotechnological potential of GRFs requires a thorough understanding of the various regulatory layers governing GRF activity, the functional divergence among GRF family members, and the gene networks that they regulate.

Genome-wide characterization of the GRF transcription factors in potato (Solanum tuberosum L.) and expression analysis of StGRF genes during potato tuber dormancy and sprouting

Growth-regulating factors (GRFs) are transcription factors that play a pivotal role in plant growth and development. This study identifies 12 Solanum tuberosum GRF transcription factors (StGRFs) and analyzes their physicochemical properties, phylogenetic relationships, gene structures and gene expression patterns using bioinformatics. The StGRFs exhibit a length range of 266 to 599 amino acids, with a molecular weight of 26.02 to 64.52 kDa. The majority of StGRFs possess three introns. The promoter regions contain a plethora of cis-acting elements related to plant growth and development, as well as environmental stress and hormone response. All the members of the StGRF family contain conserved WRC and QLQ domains, with the sequences of these two conserved domain modules exhibiting high levels of conservation. Transcriptomic data indicates that StGRFs play a significant role in the growth and development of stamens, roots, young tubers, and other tissues or organs in potatoes. Furthermore, a few StGRFs exhibit differential expression patterns in response to Phytophthora infestans, chemical elicitors, heat, salt, and drought stresses, as well as multiple hormone treatments. The results of the expression analysis indicate that StGRF1, StGRF2, StGRF5, StGRF7, StGRF10 and StGRF12 are involved in the process of tuber sprouting, while StGRF4 and StGRF9 may play a role in tuber dormancy. These findings offer valuable insights that can be used to investigate the roles of StGRFs during potato tuber dormancy and sprouting.

Temporal dynamics of genetic architecture governing leaf development in Populus

Leaf development is a multifaceted and dynamic process orchestrated by a myriad of genes to shape the proper size and morphology. The dynamic genetic network underlying leaf development remains largely unknown. Utilizing a synergistic genetic approach encompassing dynamic genome-wide association study (GWAS), time-ordered gene co-expression network (TO-GCN) analyses and gene manipulation, we explored the temporal genetic architecture and regulatory network governing leaf development in Populus. We identified 42 time-specific and 18 consecutive genes that displayed different patterns of expression at various time points. We then constructed eight TO-GCNs that covered the cell proliferation, transition, and cell expansion stages of leaf development. Integrating GWAS and TO-GCN, we postulated the functions of 27 causative genes for GWAS and identified PtoGRF9 as a key player in leaf development. Genetic manipulation via overexpression and suppression of PtoGRF9 revealed its primary influence on leaf development by modulating cell proliferation. Furthermore, we elucidated that PtoGRF9 governs leaf development by activating PtoHB21 during the cell proliferation stage and attenuating PtoLD during the transition stage. Our study provides insights into the dynamic genetic underpinnings of leaf development and understanding the regulatory mechanism of PtoGRF9 in this dynamic process.

Genome-Wide Identification and Expression Analysis of Growth-Regulating Factors in Eucommia ulmoides Oliver (Du-Zhong)

The roots, stems, leaves, and seeds of Eucommia ulmoides contain a large amount of trans-polyisoprene (also known as Eu-rubber), which is considered to be an important laticiferous plant with valuable industrial applications. Eu-rubber used in industry is mainly extracted from leaves. Therefore, it is of great significance to identify genes related to regulating the leaf size of E. ulmoides. Plant growth-regulating factors (GRFs) play important roles in regulating leaf size, and their functions are highly conserved across different plant species. However, there have been very limited reports on EuGRFs until now. In this study, eight canonical EuGRFs with both QLQ and WRC domains and two putative eul-miR396s were identified in the chromosome-level genome of E. ulmoides. It is found that, unlike AtGRFs, all EuGRFs contain the miR396s binding site in the terminal of WRC domains. These EuGRFs were distributed on six chromosomes in the genome of E. ulmoides. Collinearity analysis of the E. ulmoides genome revealed that EuGRF1 and EuGRF3 exhibit collinear relationships with EuGRF2, suggesting that those three genes may have emerged via gene replication events. The collinear relationship between EuGRFs, AtGRFs, and OsGRFs showed that EuGRF5 and EuGRF8 had no collinear members in Arabidopsis and rice. Almost all EuGRFs show a higher expression level in growing and developing tissues, and most EuGRF promoters process phytohormone-response and stress-induced cis-elements. Moreover, we found the expression of EuGRFs was significantly induced by gibberellins (GA3) in three hours, and the height of E. ulmoides seedlings was significantly increased one week after GA3 treatment. The findings in this study provide potential candidate genes for further research and lay the foundation for further exploring the molecular mechanism underlying E. ulmoides development in response to GA3.

Genome-wide association study and network analysis of in vitro transformation in Populus trichocarpa support key roles of diverse phytohormone pathways and cross talk

Wide variation in amenability to transformation and regeneration (TR) among many plant species and genotypes presents a challenge to the use of genetic engineering in research and breeding. To help understand the causes of this variation, we performed association mapping and network analysis using a population of 1204 wild trees of Populus trichocarpa (black cottonwood). To enable precise and high-throughput phenotyping of callus and shoot TR, we developed a computer vision system that cross-referenced complementary red, green, and blue (RGB) and fluorescent-hyperspectral images. We performed association mapping using single-marker and combined variant methods, followed by statistical tests for epistasis and integration of published multi-omic datasets to identify likely regulatory hubs. We report 409 candidate genes implicated by associations within 5 kb of coding sequences, and epistasis tests implicated 81 of these candidate genes as regulators of one another. Gene ontology terms related to protein-protein interactions and transcriptional regulation are overrepresented, among others. In addition to auxin and cytokinin pathways long established as critical to TR, our results highlight the importance of stress and wounding pathways. Potential regulatory hubs of signaling within and across these pathways include GROWTH REGULATORY FACTOR 1 (GRF1), PHOSPHATIDYLINOSITOL 4-KINASE β1 (PI-4Kβ1), and OBF-BINDING PROTEIN 1 (OBP1).

Precocious cell differentiation occurs in proliferating cells in leaf primordia in Arabidopsis angustifolia3 mutant

During leaf development, the timing of transition from cell proliferation to expansion is an important factor in determining the final organ size. However, the regulatory system involved in this transition remains less understood. To get an insight into this system, we investigated the compensation phenomenon, in which the cell number decreases while the cell size increases in organs with determinate growth. Compensation is observed in several plant species suggesting coordination between cell proliferation and expansion. In this study, we examined an Arabidopsis mutant of ANGUSTIFOLIA 3 (AN3)/GRF-INTERACTING FACTOR 1, a positive regulator of cell proliferation, which exhibits the compensation. Though the AN3 role has been extensively investigated, the mechanism underlying excess cell expansion in the an3 mutant remains unknown. Focusing on the early stage of leaf development, we performed kinematic, cytological, biochemical, and transcriptome analyses, and found that the cell size had already increased during the proliferation phase, with active cell proliferation in the an3 mutant. Moreover, at this stage, chloroplasts, vacuoles, and xylem cells developed earlier than in the wild-type cells. Transcriptome data showed that photosynthetic activity and secondary cell wall biosynthesis were activated in an3 proliferating cells. These results indicated that precocious cell differentiation occurs in an3 cells. Therefore, we suggest a novel AN3 role in the suppression of cell expansion/differentiation during the cell proliferation phase.

Nuclear lamina component KAKU4 regulates chromatin states and transcriptional regulation in the Arabidopsis genome

BACKGROUND

The nuclear lamina links the nuclear membrane to chromosomes and plays a crucial role in regulating chromatin states and gene expression. However, current knowledge of nuclear lamina in plants is limited compared to animals and humans.

RESULTS

This study mainly focused on elucidating the mechanism through which the putative nuclear lamina component protein KAKU4 regulates chromatin states and gene expression in Arabidopsis leaves. Thus, we constructed a network using the association proteins of lamin-like proteins, revealing that KAKU4 is strongly associated with chromatin or epigenetic modifiers. Then, we conducted ChIP-seq technology to generate global epigenomic profiles of H3K4me3, H3K27me3, and H3K9me2 in Arabidopsis leaves for mutant (kaku4-2) and wild-type (WT) plants alongside RNA-seq method to generate gene expression profiles. The comprehensive chromatin state-based analyses indicate that the knockdown of KAKU4 has the strongest effect on H3K27me3, followed by H3K9me2, and the least impact on H3K4me3, leading to significant changes in chromatin states in the Arabidopsis genome. We discovered that the knockdown of the KAKU4 gene caused a transition between two types of repressive epigenetics marks, H3K9me2 and H3K27me3, in some specific PLAD regions. The combination analyses of epigenomic and transcriptomic data between the kaku4-2 mutant and WT suggested that KAKU4 may regulate key biological processes, such as programmed cell death and hormone signaling pathways, by affecting H3K27me3 modification in Arabidopsis leaves.

CONCLUSIONS

In summary, our results indicated that KAKU4 is directly and/or indirectly associated with chromatin/epigenetic modifiers and demonstrated the essential roles of KAKU4 in regulating chromatin states, transcriptional regulation, and diverse biological processes in Arabidopsis.

Comparative genomic analysis of the Growth-Regulating Factors-Interacting Factors (GIFs) in six Salicaceae species and functional analysis of PeGIF3 reveals their regulatory role in Populus heteromorphic leaves

BACKGROUND

The growth-regulating factor-interacting factor (GIF) gene family plays a vital role in regulating plant growth and development, particularly in controlling leaf, seed, and root meristem homeostasis. However, the regulatory mechanism of heteromorphic leaves by GIF genes in Populus euphratica as an important adaptative trait of heteromorphic leaves in response to desert environment remains unknown.

RESULTS

This study aimed to identify and characterize the GIF genes in P. euphratica and other five Salicaceae species to investigate their role in regulating heteromorphic leaf development. A total of 27 GIF genes were identified and characterized across six Salicaceae species (P. euphratica, Populus pruinose, Populus deltoides, Populus trichocarpa, Salix sinopurpurea, and Salix suchowensis) at the genome-wide level. Comparative genomic analysis among these species suggested that the expansion of GIFs may be derived from the specific Salicaceae whole-genome duplication event after their divergence from Arabidopsis thaliana. Furthermore, the expression data of PeGIFs in heteromorphic leaves, combined with functional information on GIF genes in Arabidopsis, indicated the role of PeGIFs in regulating the leaf development of P. euphratica, especially PeGIFs containing several cis-acting elements associated with plant growth and development. By heterologous expression of the PeGIF3 gene in wild-type plants (Col-0) and atgif1 mutant of A. thaliana, a significant difference in leaf expansion along the medial-lateral axis, and an increased number of leaf cells, were observed between the overexpressed plants and the wild type.

CONCLUSION

PeGIF3 enhances leaf cell proliferation, thereby resulting in the expansion of the central-lateral region of the leaf. The findings not only provide global insights into the evolutionary features of Salicaceae GIFs but also reveal the regulatory mechanism of PeGIF3 in heteromorphic leaves of P. euphratica.

A rapid and highly efficient sorghum transformation strategy using GRF4-GIF1/ternary vector system

Sorghum is an important crop for food, forage, wine and biofuel production. To enhance its transformation efficiency without negative developmental by-effects, we investigated the impact of GRF4-GIF1 chimaera and GRF5 on sorghum transformation. Both GRF4-GIF1 and GRF5 effectively improved the transformation efficiency of sorghum and accelerated the transformation process of sorghum to less than 2 months which was not observed when using BBM-WUS. As agrobacterium  effectors increase the ability of T-DNA transfer into plant cells, we checked whether ternary vector system can additively enhance sorghum transformation. The combination of GRF4-GIF1 with helper plasmid pVS1-VIR2 achieved the highest transformation efficiency, reaching 38.28%, which is 7.71-fold of the original method. Compared with BBM-WUS, overexpressing GRF4-GIF1 caused no noticeable growth defects in sorghum. We further developed a sorghum CRISPR/Cas9 gene-editing tool based on this GRF4-GIF1/ternary vector system, which achieved an average gene mutation efficiency of 41.36%, and null mutants were created in the T0 generation.

The Emerging Role of Non-Coding RNAs (ncRNAs) in Plant Growth, Development, and Stress Response Signaling

Plant species utilize a variety of regulatory mechanisms to ensure sustainable productivity. Within this intricate framework, numerous non-coding RNAs (ncRNAs) play a crucial regulatory role in plant biology, surpassing the essential functions of RNA molecules as messengers, ribosomal, and transfer RNAs. ncRNAs represent an emerging class of regulators, operating directly in the form of small interfering RNAs (siRNAs), microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs). These ncRNAs exert control at various levels, including transcription, post-transcription, translation, and epigenetic. Furthermore, they interact with each other, contributing to a variety of biological processes and mechanisms associated with stress resilience. This review primarily concentrates on the recent advancements in plant ncRNAs, delineating their functions in growth and development across various organs such as root, leaf, seed/endosperm, and seed nutrient development. Additionally, this review broadens its scope by examining the role of ncRNAs in response to environmental stresses such as drought, salt, flood, heat, and cold in plants. This compilation offers updated information and insights to guide the characterization of the potential functions of ncRNAs in plant growth, development, and stress resilience in future research.

Non-coding RNAs and leaf senescence: Small molecules with important roles

Non-coding RNAs (ncRNAs) are a special class of functional RNA molecules that are not translated into proteins. ncRNAs have emerged as pivotal regulators of diverse developmental processes in plants. Recent investigations have revealed the association of ncRNAs with the regulation of leaf senescence, a complex and tightly regulated developmental process. However, a comprehensive review of the involvement of ncRNAs in the regulation of leaf senescence is still lacking. This manuscript aims to summarize the molecular mechanisms underlying ncRNAs-mediated leaf senescence and the potential applications of ncRNAs to manipulate the onset and progression of leaf senescence. Various classes of ncRNAs, including microRNAs (miRNAs), small interfering RNAs (siRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), are discussed in terms of their regulatory mechanisms in leaf senescence. Furthermore, we explore the interactions between ncRNA and the key regulators of senescence, including transcription factors as well as core components in phytohormone signaling pathways. We also discuss the possible challenges and approaches related to ncRNA-mediated leaf senescence. This review contributes to a further understanding of the intricate regulatory network involving ncRNAs in leaf senescence.

Multi-omics analysis of small RNA, transcriptome, and degradome to identify putative miRNAs linked to MeJA regulated and oridonin biosynthesis in Isodon rubescens

Isodon rubescens has garnered much attention due to its anti-tumor or anti-cancer properties. However, little is known about the molecular mechanism of oridonin biosynthesis leveraging the regulatory network between small RNAs and mRNAs. In this study, the regulatory networks of miRNAs and targets were examined by combining mRNA, miRNA, and degradome. A total of 348 miRNAs, including 287 known miRNAs and 61 novel miRNAs, were identified. Among them, 51 miRNAs were significantly expressed, and 36 miRNAs responded to MeJA. A total of 3066 target genes were associated with 228 miRNAs via degradome sequencing. Multi-omics analysis demonstrated that 27 miRNA-mRNA pairs were speculated to be involved in MeJA regulation, and 36 miRNA-mRNA pairs were hypothesized to be involved in the genotype-dependence of I. rubescens. Furthermore, 151 and 7 miRNA-mRNA modules were likely engaged in oridonin biosynthesis as identified by psRNATarget and degradome sequencing, respectively. Some miRNA-mRNA modules were confirmed via RT-qPCR. Moreover, miRNAs targeting plant hormone signal transduction pathway genes were identified, such as miR156, miR167, miR393, and PC-3p-19822_242. Collectively, our results demonstrate for the first time that miRNAs are identified in I. rubescens, and laid a solid foundation for further research on the molecular mechanism of oridonin biosynthesis mediated by miRNA.

Leaf growth - complex regulation of a seemingly simple process

Understanding the underlying mechanisms of plant development is crucial to successfully steer or manipulate plant growth in a targeted manner. Leaves, the primary sites of photosynthesis, are vital organs for many plant species, and leaf growth is controlled by a tight temporal and spatial regulatory network. In this review, we focus on the genetic networks governing leaf cell proliferation, one major contributor to final leaf size. First, we provide an overview of six regulator families of leaf growth in Arabidopsis: DA1, PEAPODs, KLU, GRFs, the SWI/SNF complexes, and DELLAs, together with their surrounding genetic networks. Next, we discuss their evolutionary conservation to highlight similarities and differences among species, because knowledge transfer between species remains a big challenge. Finally, we focus on the increase in knowledge of the interconnectedness between these genetic pathways, the function of the cell cycle machinery as their central convergence point, and other internal and environmental cues.

miRNAs and genes as molecular regulators of rice grain morphology and yield

Rice is one of the most consumed crops worldwide and the genetic and molecular basis of its grain yield attributes are well understood. Various studies have identified different yield-related parameters in rice that are regulated by the microRNAs (miRNAs). MiRNAs are endogenous small non-coding RNAs that silence gene expression during or after transcription. They control a variety of biological or genetic activities in plants including growth, development and response to stress. In this review, we have summarized the available information on the genetic control of panicle architecture and grain yield (number and morphology) in rice. The miRNA nodes that are associated with their regulation are also described while focussing on the central role of miR156-SPL node to highlight the co-regulation of two master regulators that determine the fate of panicle development. Since abiotic stresses are known to negatively affect yield, the impact of abiotic stress induced alterations on the levels of these miRNAs are also discussed to highlight the potential of miRNAs for regulating crop yields.

Emerging roles of plant microRNAs during Colletotrichum spp. infection

MAIN CONCLUSION

This review provides valuable insights into plant molecular regulatory mechanisms during fungus attacks, highlighting potential miRNA candidates for future disease management. Plant defense responses to biotic stress involve intricate regulatory mechanisms, including post-transcriptional regulation of genes mediated by microRNAs (miRNAs). These small RNAs play a vital role in the plant's innate immune system, defending against viral, bacterial, and fungal attacks. Among the plant pathogenic fungi, Colletotrichum spp. are notorious for causing anthracnose, a devastating disease affecting economically important crops worldwide. Understanding the molecular machinery underlying the plant immune response to Colletotrichum spp. is crucial for developing tools to reduce production losses. In this comprehensive review, we examine the current understanding of miRNAs associated with plant defense against Colletotrichum spp. We summarize the modulation patterns of miRNAs and their respective target genes. Depending on the function of their targets, miRNAs can either contribute to host resistance or susceptibility. We explore the multifaceted roles of miRNAs during Colletotrichum infection, including their involvement in R-gene-dependent immune system responses, hormone-dependent defense mechanisms, secondary metabolic pathways, methylation regulation, and biosynthesis of other classes of small RNAs. Furthermore, we employ an integrative approach to correlate the identified miRNAs with various strategies and distinct phases of fungal infection. This study provides valuable insights into the current understanding of plant miRNAs and their regulatory mechanisms during fungus attacks.

Genome-wide molecular evolution analysis of the GRF and GIF gene families in Plantae (Archaeplastida)

BACKGROUND

Plant growth-regulating factors (GRFs) and GRF-interacting factors (GIFs) interact with each other and collectively have important regulatory roles in plant growth, development, and stress responses. Therefore, it is of great significance to explore the systematic evolution of GRF and GIF gene families. However, our knowledge and understanding of the role of GRF and GIF genes during plant evolution has been fragmentary.

RESULTS

In this study, a large number of genomic and transcriptomic datasets of algae, mosses, ferns, gymnosperms and angiosperms were used to systematically analyze the evolution of GRF and GIF genes during the evolution of plants. The results showed that GRF gene first appeared in the charophyte Klebsormidium nitens, whereas the GIF genes originated relatively early, and these two gene families were mainly expanded by segmental duplication events after plant terrestrialization. During the process of evolution, the protein sequences and functions of GRF and GIF family genes are relatively conservative. As cooperative partner, GRF and GIF genes contain the similar types of cis-acting elements in their promoter regions, which enables them to have similar transcriptional response patterns, and both show higher levels of expression in reproductive organs and tissues and organs with strong capacity for cell division. Based on protein-protein interaction analysis and verification, we found that the GRF-GIF protein partnership began to be established in pteridophytes and is highly conserved across different terrestrial plants.

CONCLUSIONS

These results provide a foundation for further exploration of the molecular evolution and biological functions of GRF and GIF genes.

AsHSP26.2, a creeping bentgrass chloroplast small heat shock protein positively regulates plant development

KEY MESSAGE

The creeping bentgrass small heat shock protein AsHSP26.2 positively regulates plant growth and is a novel candidate for use in crop genetic engineering for enhanced biomass production and grain yield. Small heat shock proteins (sHSPs), a family of proteins with high level of diversity, significantly influence plant stress tolerance and plant development. We have cloned a creeping bentgrass chloroplast-localized sHSP gene, AsHSP26.2 responsive to IAA, GA and 6-BA stimulation. Transgenic creeping bentgrass overexpressing AsHSP26.2 exhibited significantly enhanced plant growth with increased stolon number and length as well as enlarged leaf blade width and leaf sheath diameters, but inhibited leaf trichomes initiation and development in the abaxial epidermis. These phenotypes are completely opposite to those displayed in the transgenic plants overexpressing AsHSP26.8, another chloroplast sHSP26 isoform that contains additional seven amino acids (AEGQGDG) between the consensus regions III and IV (Sun et al., Plant Cell Environ 44:1769-1787, 2021). Furthermore, AsHSP26.2 overexpression altered phytohormone biosynthesis and signaling transduction, resulting in elevated auxin and gibberellins (GA) accumulation. The results obtained provide novel insights implicating the sHSPs in plant growth and development regulation, and strongly suggest AsHSP26.2 to be a novel candidate for use in crop genetic engineering for enhanced plant biomass production and grain yield.

Genome-wide identification of GROWTH-REGULATING FACTORs in Liriodendron chinense and functional characterization of LcGRF2 in leaf size regulation

GROWTH-REGULATING FACTORs (GRFs) play a pivotal role in the regulation of leaf size in plants and have been widely reported in plants. However, their specific functions in leaf size regulation in Liriodendron chinense remains unclear. Therefore, in this study, we identified GRF genes on a genome-wide scale in L. chinense to characterize the roles of LcGRFs in regulating leaf size. A total of nine LcGRF genes were identified, and these genes exhibited weak expression in mature leaves but strong expression in shoot apex. Notably, LcGRF2 exhibited the highest expression level in the shoot apex of L. chinense. Further RT-qPCR assay revealed that the expression level of LcGRF2 gradually decreased along with the leaf development process, and also displayed a gradient along the leaf proximo-distal and medio-lateral axes. Furthermore, overexpression of LcGRF2 in Arabidopsis thaliana resulted in increased leaf size, and significantly up-regulated the expression of genes involved in cell division like AtCYCD3;1, AtKNOLLE, and AtCYCB1;1, indicating that LcGRF2 may influence leaf size by promoting cell proliferation. This work contributes to a better understanding of the roles and molecular mechanisms of LcGRFs in the regulation of leaf size in L. chinense.

Growing Conditions and Varietal Ecologies Differently Regulates the Growth-regulating-factor (GRFs) Gene Family in Rice

Background

Growth-regulating factors (GRFs) are crucial in rice for controlling plant growth and development. Among the rice cultivation practices, aerobic methods are water efficient but result in significant yield reduction relative to non-aerobic cultivation. Therefore, mechanistic insights into aerobic rice cultivation are important for improving the aerobic performance of rice.

Objectives

This study aimed to examine the evolution of GRFs in different rice species, analyse the phenotypic differences between aerobic and non-aerobic conditions in three rice varieties, and assess the expression of GRFs in these varieties under both aerobic and non-aerobic conditions.

Materials and Methods

This study comprehensively examined the GRFs gene family in 11 rice species (Oryza barthii, Oryza brachyantha, Oryza glaberrima, Oryza glumipatula, Oryza sativa subsp. indica, Oryza longistaminata, Oryza meridionalis, Oryza nivara, Oryza punctata, Oryza rufipogon, Oryza sativa subsp. japonica) focusing on phylogenetic analysis. Additionally, the expression patterns of 12 GRFs were investigated in three distinct genotypes of O. sativa subsp. indica rice, under both non-aerobic and aerobic conditions.

Results

Three major phylogenetic clades were formed based on conserved motifs in the 123 GRFs proteins in eleven rice species. Further, novel motifs were identified especially in O. longistaminata indicative of the species level evolutionary differences in rice. Among the trait performance, the number of tillers was reduced by ~ 36% under aerobic conditions, but the reduction was found to be less in CR Dhan 201, an aerobic variety. Besides, three GRFs namely GRF3, GRF4, and GRF7 were found to be distinct in expression between aerobic and non-aerobic conditions.

Conclusion

Three GRF genes namely GRF3, GRF4, and GRF7 could be associated with the aerobic adaptation in rice.

Genome-wide identification and expression analysis of growth-regulating factors in Dendrobium officinale and Dendrobium chrysotoxum

Background

Dendrobium, one of the largest genera in Orchidaceae, is popular not only for its aesthetic appeal but for its significant medicinal value. Growth-regulating factors (GRFs) play an essential role in plant growth and development. However, there is still a lack of information about the evolution and biological function analysis of the GRF gene family among Dendrobiumspecies.

Methods

Growth-regulating factors from Dendrobium officinale Kimura et Migo and Dendrobium chrysotoxum Lindl. were identified by HMMER and BLAST. Detailed bioinformatics analysis was conducted to explore the evolution and function of GRF gene family in D. officinale and D. chrysotoxum using genomic data, transcriptome data and qRT-PCR technology.

Results

Here, we evaluated the evolution of the GRF gene family based on the genome sequences of D. officinale and D. chrysotoxum. Inferred from phylogenetic trees, the GRF genes were classified into two clades, and each clade contains three subclades. Sequence comparison analysis revealed relatively conserved gene structures and motifs among members of the same subfamily, indicating a conserved evolution of GRF genes within Dendrobiumspecies. However, considering the distribution of orthologous DoGRFs and DcGRFs, and the differences in the number of GRFs among species, we suggest that the GRF gene family has undergone different evolutionary processes. A total of 361 cis-elements were detected, with 33, 141, and 187 related to plant growth and development, stress, and hormones, respectively. The tissue-specific expression of GRFs showed that DoGRF8 may have a significant function in the stem elongation of D. officinale. Moreover, four genes were up-regulated under Methyl-jasmonic acid/methyl jasmonate (MeJA) treatment, showing that DoGRFs and DcGRFs play a crucial role in stress response. These findings provide valuable information for further investigations into the evolution and function of GRF genes in D. officinale and D. chrysotoxum.

Overview of molecular mechanisms of plant leaf development: a systematic review

Leaf growth initiates in the peripheral region of the meristem at the apex of the stem, eventually forming flat structures. Leaves are pivotal organs in plants, serving as the primary sites for photosynthesis, respiration, and transpiration. Their development is intricately governed by complex regulatory networks. Leaf development encompasses five processes: the leaf primordium initiation, the leaf polarity establishment, leaf size expansion, shaping of leaf, and leaf senescence. The leaf primordia starts from the side of the growth cone at the apex of the stem. Under the precise regulation of a series of genes, the leaf primordia establishes adaxial-abaxial axes, proximal-distal axes and medio-lateral axes polarity, guides the primordia cells to divide and differentiate in a specific direction, and finally develops into leaves of a certain shape and size. Leaf senescence is a kind of programmed cell death that occurs in plants, and as it is the last stage of leaf development. Each of these processes is meticulously coordinated through the intricate interplay among transcriptional regulatory factors, microRNAs, and plant hormones. This review is dedicated to examining the regulatory influences of major regulatory factors and plant hormones on these five developmental aspects of leaves.

Genome-Wide Analysis of Flax (Linum usitatissimum L.) Growth-Regulating Factor (GRF) Transcription Factors

Flax is an important cash crop globally with a variety of commercial uses. It has been widely used for fiber, oil, nutrition, feed and in composite materials. Growth regulatory factor (GRF) is a transcription factor family unique to plants, and is involved in regulating many processes of growth and development. Bioinformatics analysis of the GRF family in flax predicted 17 LuGRF genes, which all contained the characteristic QLQ and WRC domains. Equally, 15 of 17 LuGRFs (88%) are predicted to be regulated by lus-miR396 miRNA. Phylogenetic analysis of GRFs from flax and several other well-characterized species defined five clades; LuGRF genes were found in four clades. Most LuGRF gene promoters contained cis-regulatory elements known to be responsive to hormones and stress. The chromosomal locations and collinearity of LuGRF genes were also analyzed. The three-dimensional structure of LuGRF proteins was predicted using homology modeling. The transcript expression data indicated that most LuGRF family members were highly expressed in flax fruit and embryos, whereas LuGRF3, LuGRF12 and LuGRF16 were enriched in response to salt stress. Real-time quantitative fluorescent PCR (qRT-PCR) showed that both LuGRF1 and LuGRF11 were up-regulated under ABA and MeJA stimuli, indicating that these genes were involved in defense. LuGRF1 was demonstrated to be localized to the nucleus as expected for a transcription factor. These results provide a basis for further exploration of the molecular mechanism of LuGRF gene function and obtaining improved flax breeding lines.

Design principles for synthetic control systems to engineer plants

KEY MESSAGE

Synthetic control systems have led to significant advancement in the study and engineering of unicellular organisms, but it has been challenging to apply these tools to multicellular organisms like plants. The ability to predictably engineer plants will enable the development of novel traits capable of alleviating global problems, such as climate change and food insecurity. Engineering predictable multicellular phenotypes will require the development of synthetic control systems that can precisely regulate how the information encoded in genomes is translated into phenotypes. Many efficient control systems have been developed for unicellular organisms. However, it remains challenging to use such tools to study or engineer multicellular organisms. Plants are a good chassis within which to develop strategies to overcome these challenges, thanks to their capacity to withstand large-scale reprogramming without lethality. Additionally, engineered plants have great potential for solving major societal problems. Here we briefly review the progress of control system development in unicellular organisms, and how that information can be leveraged to characterize control systems in plants. Further, we discuss strategies for developing control systems designed to regulate the expression of transgenes or endogenous loci and generate dosage-dependent or discrete traits. Finally, we discuss the utility that mathematical models of biological processes have for control system deployment.

Epigenetic control of plant senescence and cell death and its application in crop improvement

Plant senescence is the last stage of plant development and a type of programmed cell death, occurring at a predictable time and cell. It involves the functional conversion from nutrient assimilation to nutrient remobilization, which substantially impacts plant architecture and plant biomass, crop quality, and horticultural ornamental traits. In past two decades, DNA damage was believed to be a main reason for cell senescence. Increasing evidence suggests that the alteration of epigenetic information is a contributing factor to cell senescence in organisms. In this review, we summarize the current research progresses of epigenetic and epitranscriptional mechanism involved in cell senescence of plant, at the regulatory level of DNA methylation, histone methylation and acetylation, chromatin remodeling, non-coding RNAs and RNA methylation. Furthermore, we discuss their molecular genetic manipulation and potential application in agriculture for crop improvement. Finally we point out the prospects of future research topics.

The meso-octoploid Heliophila variabilis genome sheds a new light on the impact of polyploidization and diploidization on the diversity of the Cape flora

Although the South African Cape flora is one of the most remarkable biodiversity hotspots, its high diversity has not been associated with polyploidy. Here, we report the chromosome-scale genome assembly of an ephemeral cruciferous species Heliophila variabilis (~334 Mb, n = 11) adapted to South African semiarid biomes. Two pairs of differently fractionated subgenomes suggest an allo-octoploid origin of the genome at least 12 million years ago. The ancestral octoploid Heliophila genome (2n = 8x = ~60) has probably originated through hybridization between two allotetraploids (2n = 4x = ~30) formed by distant, intertribal, hybridization. Rediploidization of the ancestral genome was marked by extensive reorganization of parental subgenomes, genome downsizing, and speciation events in the genus Heliophila. We found evidence for loss-of-function changes in genes associated with leaf development and early flowering, and over-retention and sub/neofunctionalization of genes involved in pathogen response and chemical defense. The genomic resources of H. variabilis will help elucidate the role of polyploidization and genome diploidization in plant adaptation to hot arid environments and origin of the Cape flora. The sequenced H. variabilis represents the first chromosome-scale genome assembly of a meso-octoploid representative of the mustard family.