The OsmiRNA166b-OsHox32 pair regulates mechanical strength of rice plants by modulating cell wall biosynthesis

MicroRNA166: Old Players and New Insights into Crop Agronomic Traits Improvement

MicroRNA (miRNA), a type of non-coding RNA, is crucial for controlling gene expression. Among the various miRNA families, miR166 stands out as a highly conserved group found in both model and crop plants. It plays a key role in regulating a wide range of developmental and environmental responses. In this review, we explore the diverse sequences of MIR166s in major crops and discuss the important regulatory functions of miR166 in plant growth and stress responses. Additionally, we summarize how miR166 interacts with other miRNAs and highlight the potential for enhancing agronomic traits by manipulating the expression of miR166 and its targeted HD-ZIP III genes.

Knockdown of microRNA390 Enhances Maize Brace Root Growth

Brace root architecture is a critical determinant of maize's stalk anchorage and nutrition uptake, influencing root lodging resistance, stress tolerance, and plant growth. To identify the key microRNAs (miRNAs) in control of maize brace root growth, we performed small RNA sequencing using brace root samples at emergence and growth stages. We focused on the genetic modulation of brace root development in maize through manipulation of miR390 and its downstream regulated auxin response factors (ARFs). In the present study, miR167, miR166, miR172, and miR390 were identified to be involved in maize brace root growth in inbred line B73. Utilizing short tandem target mimic (STTM) technology, we further developed maize lines with reduced miR390 expression and analyzed their root architecture compared to wild-type controls. Our findings show that STTM390 maize lines exhibit enhanced brace root length and increased whorl numbers. Gene expression analyses revealed that the suppression of miR390 leads to upregulation of its downstream regulated ARF genes, specifically ZmARF11 and ZmARF26, which may significantly alter root architecture. Additionally, loss-of-function mutants for ZmARF11 and ZmARF26 were characterized to further confirm the role of these genes in brace root growth. These results demonstrate that miR390, ZmARF11, and ZmARF26 play crucial roles in regulating maize brace root growth; the involved complicated molecular mechanisms need to be further explored. This study provides a genetic basis for breeding maize varieties with improved lodging resistance and adaptability to diverse agricultural environments.

Triacylglycerol lipase, OsSG34, plays an important role in grain shape and appearance quality in rice

Optimal grain-appearance quality is largely determined by grain size. To date, dozens of grain size-related genes have been identified. However, the regulatory mechanism of slender grain formation is not fully clear. We identified the OsSG34 gene by map-based cloning. A 9-bp deletion on 5'-untranslated region of OsSG34, which resulted in the expression difference between the wild-type and sg34 mutant, led to the slender grains and good transparency in sg34 mutant. OsSG34 as an α/β fold triacylglycerol lipase affected the triglyceride content directly, and the components of cell wall indirectly, especially the lignin between the inner and outer lemmas in rice grains, which could affect the change in grain size by altering cell proliferation and expansion, while the change in starch content and starch granule arrangement in endosperm could affect the grain-appearance quality. Moreover, the OsERF71 was identified to directly bind to cis-element on the mutant site, thereby regulating the OsSG34 expression. Knockout of three OsSG34 homologous genes resulted in slender grains as well. The study demonstrated OsSG34, involved in lipid metabolism, affected grain size and quality. Our findings suggest that the OsSG34 gene could be used in rice breeding for high yield and good grain-appearance quality via marker-assisted selection and gene-editing approaches.

Tapping into the plasticity of plant architecture for increased stress resilience

Plant architecture develops post-embryonically and emerges from a dialogue between the developmental signals and environmental cues. Length and branching of the vegetative and reproductive tissues were the focus of improvement of plant performance from the early days of plant breeding. Current breeding priorities are changing, as we need to prioritize plant productivity under increasingly challenging environmental conditions. While it has been widely recognized that plant architecture changes in response to the environment, its contribution to plant productivity in the changing climate remains to be fully explored. This review will summarize prior discoveries of genetic control of plant architecture traits and their effect on plant performance under environmental stress. We review new tools in phenotyping that will guide future discoveries of genes contributing to plant architecture, its plasticity, and its contributions to stress resilience. Subsequently, we provide a perspective into how integrating the study of new species, modern phenotyping techniques, and modeling can lead to discovering new genetic targets underlying the plasticity of plant architecture and stress resilience. Altogether, this review provides a new perspective on the plasticity of plant architecture and how it can be harnessed for increased performance under environmental stress.

The miRNA-mRNA Regulatory Modules of Pinus massoniana Lamb. in Response to Drought Stress

Masson pine (Pinus massoniana Lamb.) is a major fast-growing woody tree species and pioneer species for afforestation in barren sites in southern China. However, the regulatory mechanism of gene expression in P. massoniana under drought remains unclear. To uncover candidate microRNAs, their expression profiles, and microRNA-mRNA interactions, small RNA-seq was used to investigate the transcriptome from seedling roots under drought and rewatering in P. massoniana. A total of 421 plant microRNAs were identified. Pairwise differential expression analysis between treatment and control groups unveiled 134, 156, and 96 differential expressed microRNAs at three stages. These constitute 248 unique microRNAs, which were subsequently categorized into six clusters based on their expression profiles. Degradome sequencing revealed that these 248 differentially expressed microRNAs targeted 2069 genes. Gene Ontology enrichment analysis suggested that these target genes were related to translational and posttranslational regulation, cell wall modification, and reactive oxygen species scavenging. miRNAs such as miR482, miR398, miR11571, miR396, miR166, miRN88, and miRN74, along with their target genes annotated as F-box/kelch-repeat protein, 60S ribosomal protein, copper-zinc superoxide dismutase, luminal-binding protein, S-adenosylmethionine synthase, and Early Responsive to Dehydration Stress may play critical roles in drought response. This study provides insights into microRNA responsive to drought and rewatering in Masson pine and advances the understanding of drought tolerance mechanisms in Pinus.

Rice miR5504 regulates plant height by affecting cell proliferation and expansion

miRNAs play critical roles in the regulation of plant growth and development by cleaving mRNA or repressing transcription. In our previous study, miR5504 with unknown functions was captured by small RNA sequencing. Here, the function and characters of miR5504 were extensively analyzed using CRISPR/Cas9, overexpression strategy, Northern blot, cytological analysis, and transcriptomics analysis. We found that the dwarf phenotype of mir5504 mutants (mir5504-1 and mir5504-2) appeared on 35-day seedlings and became more apparent at the mature stage. The cytological results showed a substantial decrease in the vascular bundle number, cell number and cell length in the mir5504 mutant compared with NIP. In addition, we found that miR5504 regulated plant height by targeting LOC_Os08g16914. The results of RNA-seq revealed that numerous biological processes were mainly enriched, including DNA-binding transcription factor activity, transferase activity, regulation of transcription, metabolic process, and protein binding. Meanwhile, KEEG analysis showed that numerous proteins were associated with cellular processes and metabolism pathways. Taken together, miR5504 may be involved in the regulation of plant height by affecting cell expansion and division of internode in rice.

Revitalizing miRNAs mediated agronomical advantageous traits improvement in rice

One of the key enigmas in conventional and modern crop improvement programmes is how to introduce beneficial traits without any penalty impairment. Rice (Oryza sativa L.), among the essential staple food crops grown and utilized worldwide, needs to improve genotypes in multifaceted ways. With the global view to feed ten billion under the climatic perturbation, only a potent functional master regulator can withstand with hope for the next green revolution and food security. miRNAs are such, miniature, fine tuners for crop improvement and provide a value addition in emerging technologies, namely large-scale genotyping, phenotyping, genome editing, marker-assisted selection, and genomic selection, to make rice production feasible. There has been surplus research output generated since the last decade on miRNAs in rice, however, recent functional knowledge is limited to reaping the benefits for conventional and modern improvements in rice to avoid ambiguity and redundancy in the generated data. Here, we present the latest functional understanding of miRNAs in rice. In addition, their biogenesis, intra- and inter-kingdom signaling and communication, implication of amiRNAs, and consequences upon integration with CRISPR-Cas9. Further, highlights refer to the application of miRNAs for rice agronomical trait improvements, broadly classified into three functional domains. The majority of functionally established miRNAs are responsible for growth and development, followed by biotic and abiotic stresses. Tabular cataloguing reveals and highlights two multifaceted modules that were extensively studied. These belong to miRNA families 156 and 396, orchestrate multifarious aspects of advantageous agronomical traits. Moreover, updated and exhaustive functional aspects of different supplemental miRNA modules that would strengthen rice improvement are also being discussed.

ZmHOX32 is related to photosynthesis and likely functions in plant architecture of maize

HOX32, a member of the HD-ZIP III family, functions in the leaf morphogenesis and plant photosynthesis. However, the regulatory mechanism of HOX32 in maize has not been studied and the regulatory relationship in photosynthesis is unclear. We conducted a comprehensive study, including phylogenetic analysis, expression profiling at both transcriptome and translatome levels, subcellular localization, tsCUT&Tag, co-expression analysis, and association analysis with agronomic traits on HOX32 for the dissection of the functional roles of HOX32. ZmHOX32 shows conservation in plants. As expected, maize HOX32 protein is specifically expressed in the nucleus. ZmHOX32 showed constitutively expression at both transcriptome and translatome levels. We uncovered the downstream target genes of ZmHOX32 by tsCUT&Tag and constructed a cascaded regulatory network combining the co-expression networks. Both direct and indirect targets of ZmHOX32 showed significant gene ontology enrichment in terms of photosynthesis in maize. The association study suggested that ZmHOX32 plays an important role in regulation of plant architecture. Our results illustrate a complex regulatory network of HOX32 involving in photosynthesis and plant architecture, which deepens our understanding of the phenotypic variation in plants.

Genome-wide characterization and expression analysis of MYB transcription factors in Chrysanthemum nankingense

BACKGROUND

Chrysanthemum is a popular ornamental plant worldwide. MYB (v-myb avian myeloblastosis viral oncogene homolog) transcription factors play an important role in everything from stress resistance to plant growth and development. However, the MYB family of chrysanthemums has not been the subject of a detailed bioinformatics and expression investigation.

RESULTS

In this study, we examined 324 CnMYB transcription factors from Chrysanthemum nankingense genome data, which contained 122 Cn1R-MYB, 183 CnR2R3-MYB, 12 Cn3R-MYB, 2 Cn4R-MYB, and 5 atypical CnMYB. The protein motifs and classification of CnMYB transcription factors were analyzed. Among them, motifs 1, 2, 3, and 4 were found to encode the MYB DNA-binding domain in R2R3-MYB proteins, while in other-MYB proteins, the motifs 1, 2, 3, 4, 5, 6, 7, and 8 encode the MYB DNA-binding domain. Among all CnMYBs, 44 genes were selected due to the presence of CpG islands, while methylation is detected in three genes, including CnMYB9, CnMYB152, and CnMYB219. We analyzed the expression levels of each CnMYB gene in ray floret, disc floret, flower bud, leaf, stem, and root tissues. Based on phylogenetic analysis and gene expression analysis, three genes appeared likely to control cellulose and lignin synthesis in stem tissue, and 16 genes appeared likely to regulate flowering time, anther, pollen development, and flower color. Fifty-one candidate genes that may be involved in stress response were identified through phylogenetic, stress-responseve motif of promoter, and qRT-PCR analyses. According to genes expression levels under stress conditions, six CnMYB genes (CnMYB9, CnMYB172, CnMYB186, CnMYB199, CnMYB219, and CnMYB152) were identified as key stress-responsive genes.

CONCLUSIONS

This research provides useful information for further functional analysis of the CnMYB gene family in chrysanthemums, as well as offers candidate genes for further study of cellulose and lignin synthesis, flowering traits, salt and drought stress mechanism.

Overview of Repressive miRNA Regulation by Short Tandem Target Mimic (STTM): Applications and Impact on Plant Biology

The application of miRNA mimic technology for silencing mature miRNA began in 2007. This technique originated from the discovery of the INDUCED BY PHOSPHATE STARVATION 1 (IPS1) gene, which was found to be a competitive mimic that prevents the cleavage of the targeted mRNA by miRNA inhibition at the post-transcriptional level. To date, various studies have been conducted to understand the molecular mimic mechanism and to improve the efficiency of this technology. As a result, several mimic tools have been developed: target mimicry (TM), short tandem target mimic (STTM), and molecular sponges (SPs). STTM is the most-developed tool due to its stability and effectiveness in decoying miRNA. This review discusses the application of STTM technology on the loss-of-function studies of miRNA and members from diverse plant species. A modified STTM approach for studying the function of miRNA with spatial-temporal expression under the control of specific promoters is further explored. STTM technology will enhance our understanding of the miRNA activity in plant-tissue-specific development and stress responses for applications in improving plant traits via miRNA regulation.

Identification and function of miRNA-mRNA interaction pairs during lateral root development of hemi-parasitic Santalum album L. seedlings

Sandalwood (Santalum album L.) is a hemi-parasitic tree species famous for its santalol and santalene, which are extracted from its heartwood and roots. The ability to understand root functionality within its branched root system would benefit the regulation of sandalwood growth and enhance the commercial value of sandalwood. Phenotypic and anatomical evidence in this study indicated that seed germination stage 4 (SG4) seemed pivotal for lateral root (LR) morphogenesis. Small RNA (sRNA) high-throughput sequencing of root tissues at three sub-stages of SG4 (lateral root primordia initiation (LRPI), lateral root primordia development (LRPD), and lateral root primordia emergence (LRPE)) was performed to identify microRNAs (miRNAs) associated with LR development. A total of 135 miRNAs, including 70 differentially expressed miRNAs (DEMs), were screened. Ten DEMs were selected to investigate transcript abundance in different organs or developmental stages. Among 100 negative DEM-mRNA interaction pairs, four targets (Sa-miR166m_2, 408d, 858a, and novel_Sa-miR8) were selected for studying cleavage sites by 5' RLM-RACE validation. The expression mode of the four miRNA-mRNA pairs was investigated after indole-3-acetic acid (IAA) treatment. IAA enhanced the abundance of homeobox-leucine-zipper protein 32 (HOX32), laccase 12 (LAC12), myeloblastosis86 (MYB86), and pectin methylesterase inhibitor6 (PMEI6) target transcripts by reducing the expression of Sa-miR166m_2, 408d, 858a, and novel_Sa-miR8 in the first 10 min. A schematic model of miRNA-regulated LR development is proposed for this hemi-parasitic species. This novel genetic information for improving sandalwood root growth and development may allow for the cultivation of fast-growing and high-yielding plantations.

Effect of the pectin contents and nanostructure on the stem straightness of two Paeonia lactiflora cultivars

Herbaceous peony (Paeonia lactiflora Pall.) is an ancient ornamental crop and, in recent decades, an emerging popular cut flower. Straight stems are a vital criterion for cut herbaceous peony selection, while many cultivars bend as the plant develops. Pectin helps maintain the mechanical strength of the cell wall. However, little is known about its role in the stem bending of herbaceous peony. Two herbaceous peony cultivars with contrasting stem morphologies ('Dong Fang Shao Nv', upright; 'Lan Tian Piao Xiang', bending gradually) at five developmental stages were used as materials to investigate the effects of pectin content and nanostructure on straightness using the carbazole colorimetric method and atomic force microscopy observations. The contents of water-soluble pectin (WSP), CDTA-soluble pectin (CSP), and sodium carbonate-soluble pectin (SSP) differed significantly between the two cultivars, and the contents and angle of the flower and branch showed correlations. For the pectin nanostructure, WSP showed agglomerates and long chains, with a higher proportion of broad agglomerates at the later stages of the bending cultivar than the upright cultivar. CSP showed branched chains, and the proportion of broad chains was higher in the upright cultivar at later stages, while CSP shape changed from agglomerates to chains in the bending cultivar. SSP mainly consisted of short linear main chains, and side chains in the upright stem were stacked, and the bent cultivar had more broad and short chains. It can be concluded that the contents, nanometric shape, and size of the three kinds of pectin are highly likely to affect herbaceous peony stem straightness. This study provides a theoretical basis for the role of pectin in the production and breeding of herbaceous peony cut flowers.

What Do We Know about Barley miRNAs?

Plant miRNAs are powerful regulators of gene expression at the post-transcriptional level, which was repeatedly proved in several model plant species. miRNAs are considered to be key regulators of many developmental, homeostatic, and immune processes in plants. However, our understanding of plant miRNAs is still limited, despite the fact that an increasing number of studies have appeared. This systematic review aims to summarize our current knowledge about miRNAs in spring barley (Hordeum vulgare), which is an important agronomical crop worldwide and serves as a common monocot model for studying abiotic stress responses as well. This can help us to understand the connection between plant miRNAs and (not only) abiotic stresses in general. In the end, some future perspectives and open questions are summarized.

AirMeasurer: open-source software to quantify static and dynamic traits derived from multiseason aerial phenotyping to empower genetic mapping studies in rice

Low-altitude aerial imaging, an approach that can collect large-scale plant imagery, has grown in popularity recently. Amongst many phenotyping approaches, unmanned aerial vehicles (UAVs) possess unique advantages as a consequence of their mobility, flexibility and affordability. Nevertheless, how to extract biologically relevant information effectively has remained challenging. Here, we present AirMeasurer, an open-source and expandable platform that combines automated image analysis, machine learning and original algorithms to perform trait analysis using 2D/3D aerial imagery acquired by low-cost UAVs in rice (Oryza sativa) trials. We applied the platform to study hundreds of rice landraces and recombinant inbred lines at two sites, from 2019 to 2021. A range of static and dynamic traits were quantified, including crop height, canopy coverage, vegetative indices and their growth rates. After verifying the reliability of AirMeasurer-derived traits, we identified genetic variants associated with selected growth-related traits using genome-wide association study and quantitative trait loci mapping. We found that the AirMeasurer-derived traits had led to reliable loci, some matched with published work, and others helped us to explore new candidate genes. Hence, we believe that our work demonstrates valuable advances in aerial phenotyping and automated 2D/3D trait analysis, providing high-quality phenotypic information to empower genetic mapping for crop improvement.

Identification of Nitrogen Starvation-Responsive miRNAs to Reveal the miRNA-Mediated Regulatory Network in Betula luminifera

Because of the immobility, plants encounter a series of stresses, such as varied nutrient concentrations in soil, which regulate plant growth, development, and phase transitions. Nitrogen (N) is one of the most limiting factors for plants, which was exemplified by the fact that low nitrogen (LN) has a great adverse effect on plant growth and development. In the present study, we explored the potential role of microRNAs (miRNAs) in response to LN stress in Betula luminifera. We identified 198 miRNAs using sRNA sequencing, including 155 known and 43 novel miRNAs. Among them, 98 known miRNAs and 31 novel miRNAs were differentially expressed after 0.5 h or 24 h of LN stress. Based on degradome data, 122 differential expressed miRNAs (DEmiRNAs) including 102 known miRNAs and 20 novel miRNAs targeted 203 genes, comprising 321 miRNA–target pairs. A big proportion of target genes were transcription factors and functional proteins, and most of the Gene Ontology terms were enriched in biological processes; moreover, one Kyoto Encyclopedia of Genes and Genomes term “ascorbate and aldarate metabolism” was significantly enriched. The expression patterns of six miRNAs and their corresponding target genes under LN stress were monitored. According to the potential function for targets of DEmiRNAs, a proposed regulatory network mediated by miRNA–target pairs under LN stress in B. luminifera was constructed. Taken together, these findings provide useful information to elucidate miRNA functions and establish a framework for exploring N signaling networks mediated by miRNAs in B. luminifera. It may provide new insights into the genetic engineering of the high use efficiency of N in forestry trees.

Cell wall integrity regulation across plant species

Plant cell walls are highly dynamic and chemically complex structures surrounding all plant cells. They provide structural support, protection from both abiotic and biotic stress as well as ensure containment of turgor. Recently evidence has accumulated that a dedicated mechanism exists in plants, which is monitoring the functional integrity of cell walls and initiates adaptive responses to maintain integrity in case it is impaired during growth, development or exposure to biotic and abiotic stress. The available evidence indicates that detection of impairment involves mechano-perception, while reactive oxygen species and phytohormone-based signaling processes play key roles in translating signals generated and regulating adaptive responses. More recently it has also become obvious that the mechanisms mediating cell wall integrity maintenance and pattern triggered immunity are interacting with each other to modulate the adaptive responses to biotic stress and cell wall integrity impairment. Here we will review initially our current knowledge regarding the mode of action of the maintenance mechanism, discuss mechanisms mediating responses to biotic stresses and highlight how both mechanisms may modulate adaptive responses. This first part will be focused on Arabidopsis thaliana since most of the relevant knowledge derives from this model organism. We will then proceed to provide perspective to what extent the relevant molecular mechanisms are conserved in other plant species and close by discussing current knowledge of the transcriptional machinery responsible for controlling the adaptive responses using selected examples.

Regulation of lignin biosynthesis by an atypical bHLH protein CmHLB in Chrysanthemum

Stem mechanical strength is one of the most important agronomic traits that affects the resistance of plants against insects and lodging, and plays an essential role in the quality and yield of plants. Several transcription factors regulate mechanical strength in crops. However, mechanisms of stem strength formation and regulation remain largely unexplored, especially in ornamental plants. In this study, we identified an atypical bHLH transcription factor CmHLB (HLH PROTEIN INVOLVED IN LIGNIN BIOSYNTHESIS) in chrysanthemum, belonging to a small bHLH sub-family - the PACLOBUTRAZOL RESISTANCE (PRE) family. Overexpression of CmHLB in chrysanthemum significantly increased mechanical strength of the stem, cell wall thickness, and lignin content, compared with the wild type. In contrast, CmHLB RNA interference lines exhibited the opposite phenotypes. RNA-seq analysis indicated that CmHLB promoted the expression of genes involved in lignin biosynthesis. Furthermore, we demonstrated that CmHLB interacted with Chrysanthemum KNOTTED ARABIDOPSIS THALIANA7 (CmKNAT7) through the KNOX2 domain, which has a conserved function, i.e. it negatively regulates secondary cell wall formation of fibres and lignin biosynthesis. Collectively, our results reveal a novel role for CmHLB in regulating lignin biosynthesis by interacting with CmKNAT7 and affecting stem mechanical strength in Chrysanthemum.

Genome-Wide Identification of the HD-ZIP III Subfamily in Upland Cotton Reveals the Involvement of GhHB8-5D in the Biosynthesis of Secondary Wall in Fiber and Drought Resistance

A subfamily of transcription factors known as HD-ZIP III plays distinct roles in the secondary cell wall biosynthesis, which could be attributed to the quality of cotton fiber and adaptation to drought stress. In this study, 18 HD-ZIP III genes were identified as genome wide from the upland cotton (Gossypium hirsutum). These genes are distributed on 14 different chromosomes, and all of them have undergone segmental duplications. Numerous cis-elements were identified in the promoter regions, which are related to phytohormone responses and abiotic stresses. Expression profiling of these genes by quantitative real-time (qRT)-PCR illustrated their differential spatial expression, with preferential expression in cotton fiber. Among these genes, GhHB8-5D was predicted to encode a protein that is targeted to the cell nucleus and having self-activation ability. In addition, the ectopic expression of GhHB8-5D or its synonymous mutant GhHB8-5Dm in Arabidopsis resulted in stunted plant growth, curly leaves, and twisted inflorescence stems. Microscopy examination revealed that the morphology of vascular bundles and deposition of secondary wall had substantially altered in stems, which is concomitant with the significant alteration in the transcription levels of secondary wall-related genes in these transgenic Arabidopsis. Further, ectopic expression of GhHB8-5D or GhHB8-5Dm in Arabidopsis also led to significant increase in green seedling rate and reduction in root length relative to wild type when the plants were grown under mimicked drought stress conditions. Taken together, our results may shed new light on the functional roles of GhHB8-5D that is attributable for secondary cell wall thickening in response to drought stress. Such a finding may facilitate a novel strategy for improving plant adaptations to environmental changes via regulating the biosynthesis of secondary cell wall.

Association mapping uncovers maize ZmbZIP107 regulating root system architecture and lead absorption under lead stress

Lead (Pb) is a highly toxic contaminant to living organisms and the environment. Excessive Pb in soils affects crop yield and quality, thus threatening human health via the food chain. Herein, we investigated Pb tolerance among a maize association panel using root bushiness (BSH) under Pb treatment as an indicator. Through a genome-wide association study of relative BSH, we identified four single nucleotide polymorphisms (SNPs) and 30 candidate genes associated with Pb tolerance in maize seedlings. Transcriptome analysis showed that four of the 30 genes were differentially responsive to Pb treatment between two maize lines with contrasting Pb tolerance. Among these, the ZmbZIP107 transcription factor was confirmed as the key gene controlling maize tolerance to Pb by using gene-based association studies. Two 5' UTR_variants in ZmbZIP107 affected its expression level and Pb tolerance among different maize lines. ZmbZIP107 protein was specifically targeted to the nucleus and ZmbZIP107 mRNA showed the highest expression in maize seedling roots among different tissues. Heterologous expression of ZmbZIP107 enhanced rice tolerance to Pb stress and decreased Pb absorption in the roots. Our study provided the basis for revelation of the molecular mechanism underlying Pb tolerance and contributed to cultivation of Pb-tolerant varieties in maize.

MicroRNA Techniques: Valuable Tools for Agronomic Trait Analyses and Breeding in Rice

MicroRNAs (miRNAs) are a class of small noncoding RNAs that regulate gene expression at the post-transcriptional level. Extensive studies have revealed that miRNAs have critical functions in plant growth, development, and stress responses and may provide valuable genetic resources for plant breeding research. We herein reviewed the development, mechanisms, and characteristics of miRNA techniques while highlighting widely used approaches, namely, the short tandem target mimic (STTM) approach. We described STTM-based advances in plant science, especially in the model crop rice, and introduced the CRISPR-based transgene-free crop breeding. Finally, we discussed the challenges and unique opportunities related to combining STTM and CRISPR technology for crop improvement and agriculture.