Comprehensive Annotation and Functional Exploration of MicroRNAs in Lettuce

Species-Specific miRNAs Contribute to the Divergence between Deciduous and Evergreen Species in Ilex

MicroRNAs (miRNAs) are pivotal regulators of gene expression, playing crucial roles in plant developmental processes and environmental responses. However, the function of miRNAs in influencing deciduous traits has been little explored. Here, we utilized sRNA-seq on two deciduous species, Ilex polyneura (Hand.-Mazz.) S. Y. Hu and Ilex asprella Champ. ex Benth., along with an evergreen species, Ilex latifolia Thunb., to identify and annotate miRNAs within these species. Our analysis revealed 162 species-specific miRNAs (termed SS-miRNAs) from 120 families, underscoring the fundamental roles and potential influence of SS-miRNAs on plant phenotypic diversity and adaptation. Notably, three SS-miRNAs in I. latifolia were found to target crucial genes within the abscission signaling pathway. Analysis of cis-regulatory elements suggested a novel regulatory relationship that may contribute to the evergreen phenotype of I. latifolia by modulating the abscission process in a light-independent manner. These findings propose a potential mechanism by which SS-miRNAs can influence the conserved abscission pathway, contributing to the phenotypic divergence between deciduous and evergreen species within the genus Ilex.

Blocking miR528 function promotes tillering and regrowth in switchgrass

MiRNAs have been reported to be the key regulators involving a wide range of biological processes in diverse plant species, but their functions in switchgrass, an important biofuel and forage crop, are largely unknown. Here, we reported the novel function of miR528, which has expanded to four copies in switchgrass, in controlling biomass trait of tillering number and regrowth rate after mowing. Blocking miR528 activity by expressing short tandem target mimic (STTM) increased tiller number and regrowth rate after mowing. The quadruple pvmir528 mutant lines derived from genome editing also showed such improved traits. Degradome and RNA-seq analysis, combined with in situ hybridization assay revealed that up-regulation of two miR528 targets coding for Cu/Zn-SOD enzymes, might be responsible for the improved traits of tillering and regrowth in pvmir528 mutant. Additionally, natural variations in the miR528-SOD interaction exist in C3 and C4 monocot species, implying the distinct regulatory strength of the miR528-SOD module during monocot evolution. Overall, our data illuminated a novel role of miR528 in controlling biomass traits and provided a new target for genetic manipulation-mediated crop improvement.

LettuceGDB: The community database for lettuce genetics and omics

As a globally popular leafy vegetable and a representative plant of the Asteraceae family, lettuce has great economic and academic significance. In the last decade, high-throughput sequencing, phenotyping, and other multi-omics data in lettuce have accumulated on a large scale, thus increasing the demand for an integrative lettuce database. Here, we report the establishment of a comprehensive lettuce database, LettuceGDB (https://www.lettucegdb.com/). As an omics data hub, the current LettuceGDB includes two reference genomes with detailed annotations; re-sequencing data from over 1000 lettuce varieties; a collection of more than 1300 worldwide germplasms and millions of accompanying phenotypic records obtained with manual and cutting-edge phenomics technologies; re-analyses of 256 RNA sequencing datasets; a complete miRNAome; extensive metabolite information for representative varieties and wild relatives; epigenetic data on the genome-wide chromatin accessibility landscape; and various lettuce research papers published in the last decade. Five hierarchically accessible functions (Genome, Genotype, Germplasm, Phenotype, and O-Omics) have been developed with a user-friendly interface to enable convenient data access. Eight built-in tools (Assembly Converter, Search Gene, BLAST, JBrowse, Primer Design, Gene Annotation, Tissue Expression, Literature, and Data) are available for data downloading and browsing, functional gene exploration, and experimental practice. A community forum is also available for information sharing, and a summary of current research progress on different aspects of lettuce is included. We believe that LettuceGDB can be a comprehensive functional database amenable to data mining and database-driven exploration, useful for both scientific research and lettuce breeding.

Identification of Species-Specific MicroRNAs Provides Insights into Dynamic Evolution of MicroRNAs in Plants

MicroRNAs (miRNAs) are an important class of regulatory small RNAs that program gene expression, mainly at the post-transcriptional level. Although sporadic examples of species-specific miRNAs (termed SS-miRNAs) have been reported, a genome-scale study across a variety of distant species has not been assessed. Here, by comprehensively analyzing miRNAs in 81 plant species phylogenetically ranging from chlorophytes to angiosperms, we identified 8048 species-specific miRNAs from 5499 families, representing over 61.2% of the miRNA families in the examined species. An analysis of the conservation from different taxonomic levels supported the high turnover rate of SS-miRNAs, even over short evolutionary distances. A comparison of the intrinsic features between SS-miRNAs and NSS-miRNAs (non-species-specific miRNAs) indicated that the AU content of mature miRNAs was the most striking difference. Our data further illustrated a significant bias of the genomic coordinates towards SS-miRNAs lying close to or within genes. By analyzing the 125,267 putative target genes for the 7966 miRNAs, we found the preferentially regulated functions of SS-miRNAs related to diverse metabolic processes. Collectively, these findings underscore the dynamic evolution of miRNAs in the species-specific lineages.

MicroRNAs: emerging regulators in horticultural crops

Horticulture is one of the oldest agricultural practices with great popularity throughout the world. Horticultural crops include fruits, vegetables, ornamental plants, as well as medicinal and beverage plants. They are cultivated for food, specific nutrition, and medical use, or for aesthetic pleasure. MicroRNAs (miRNAs), which constitute a major class of endogenous small RNAs in plants, affect a multitude of developmental and physiological processes by imparting sequence specificity to gene regulation. Over the past decade, tens of thousands of miRNAs have been identified in more than 100 horticultural crops and their critical roles in regulating quality development of diverse horticultural crops have been demonstrated. Here, we review how miRNAs have emerged as important regulators and promising tools for horticultural crop improvement.

Biocompatible Abscisic Acid-Sensing Supramolecular Hybridization Probe for Spatiotemporal Fluorescence Imaging in Plant Tissues

Achieving detection of the phytohormone abscisic acid (ABA) is of critical importance for understanding plant growth and development. We report a hybrid supramolecular fluorescent probe that uses bovine serum albumin (BSA) as a host. Aggregation-induced emission of fluorescent chromophores (AIEgens) enables luminescence in the presence of BSA. ABA and its aptamer act as a switch to trigger this fluorescent system, the strategy that exhibits high sensitivity to abscisic acid with a detection limit of 0.098 nM. The probe test strip also enables visualization of ABA content from plants by colorimetric observation with the naked eye. In particular, the high biocompatibility and small molecular size of the prepared fluorescent probe allow for effective monitoring of ABA in plant tissues by fluorescence imaging. This strategy provides a new perspective to achieve the detection of endogenous and exogenous ABA in plants and has important implications for plant biology research.

The Construction and Exploration of a Comprehensive MicroRNA Centered Regulatory Network in Foxtail Millet (Setaria italica L.)

MicroRNA (miRNA) is an essential endogenous post-transcriptional regulatory factor, and foxtail millet (Setaria italica L.) is an ideal C4 model cereal that is a highly valuable crop in semiarid and arid areas. The Research on comprehensive and high confidence identification and annotation of foxtail millet miRNAs needs to be strengthened, and to our knowledge, there is no information on the regulatory network of foxtail millet miRNA. In this study, 136 high confidence miRNAs were identified through high-throughput sequencing of the small RNAs in seven tissues at the shooting and grain filling stages of foxtail millet. A total of 2,417 target genes were obtained by combining computational biology software and degradome sequencing methods. Furthermore, an analysis using transcriptome sequencing revealed the relationships between miRNAs and their target genes and simultaneously explored key regulatory modules in panicles during the grain filling stage. An miRNA regulatory network was constructed to explore the functions of miRNA in more detail. This network, centered on miRNAs and combining upstream transcriptional factors and downstream target genes, is primarily composed of feed forward loop motifs, which greatly enhances our knowledge of the potential functions of miRNAs and uncovers numerous previously unknown regulatory links. This study provides a solid foundation for research on the function and regulatory network of miRNAs in foxtail millet.