Overexpression of microRNA319 impacts leaf morphogenesis and leads to enhanced cold tolerance in rice (Oryza sativa L.)

MicroRNA319 (miR319) family is one of the conserved microRNA (miRNA) families among diverse plant species. It has been reported that miR319 regulates plant development in dicotyledons, but little is known at present about its functions in monocotyledons. In rice (Oryza sativa L.), the MIR319 gene family comprises two members, Osa-MIR319a and Osa-MIR319b. Here, we report an expression pattern analysis and a functional characterization of the two Osa-MIR319 genes in rice. We found that overexpressing Osa-MIR319a and Osa-MIR319b in rice both resulted in wider leaf blades. Leaves of osa-miR319 overexpression transgenic plants showed an increased number of longitudinal small veins, which probably accounted for the increased leaf blade width. In addition, we observed that overexpressing osa-miR319 led to enhanced cold tolerance (4 °C) after chilling acclimation (12 °C) in transgenic rice seedlings. Notably, under both 4 and 12 °C low temperatures, Osa-MIR319a and Osa-MIR319b were down-regulated while the expression of miR319-targeted genes was induced. Furthermore, genetically down-regulating the expression of either of the two miR319-targeted genes, OsPCF5 and OsPCF8, in RNA interference (RNAi) plants also resulted in enhanced cold tolerance after chilling acclimation. Our findings in this study demonstrate that miR319 plays important roles in leaf morphogenesis and cold tolerance in rice.

Adaptation in flower form: a comparative evodevo approach

Evolutionary developmental biology (evodevo) attempts to explain how the process of organismal development evolves, utilizing a comparative approach to investigate changes in developmental pathways and processes that occur during the evolution of a given lineage. Evolutionary genetics uses a population approach to understand how organismal changes in form or function are linked to underlying genetics, focusing on changes in gene and genotype frequencies within populations and the fixation of genotypic variation into traits that define species or evoke speciation events. Microevolutionary processes, including mutation, genetic drift, natural selection and gene flow, can provide the foundation for macroevolutionary patterns observed as morphological evolution and adaptation. The temporal element linking microevolutionary processes to macroevolutionary patterns is development: an organism's genotype is converted to phenotype by ontogenetic processes. Because selection acts upon the phenotype, the connection between evolutionary genetics and developmental evolution becomes essential to understanding adaptive evolution in organismal form and function. Here, we discuss how developmental genetic studies focused on key developmental processes could be linked within a comparative framework to study the developmental genetics of adaptive evolution, providing examples from research on two key processes of plant evodevo - floral symmetry and organ fusion - and their role in the adaptation of floral form.

Analysis of the CYC/TB1 class of TCP transcription factors in basal angiosperms and magnoliids

Flower monosymmetry contributes to specialized interactions between plants and their insect pollinators. In the magnoliids, flower monosymmetry is exhibited only in the Aristolochiaceae (Piperales). Aristolochia flowers develop a calyx-derived monosymmetric perianth that enhances pollination success by a flytrap mechanism. Aristolochia arborea forms additionally a special perianth outgrowth that mimics a mushroom to attract flies, the mushroom mimicry structure (MMS). In core eudicots, members of the CYC2 clade of TCP transcription factors are key regulators of corolla monosymmetry establishment. The CYC2 clade arose via core eudicot-specific duplications from ancestral CYC/TB1 genes. CYC/TB1 genes are also thought to affect monosymmetry formation in early diverging eudicot and monocot species. Here, we demonstrate that CYC/TB1 genes, named CYC-like genes (CYCL) are present in basal angiosperms and magnoliids. Expression analyses in A. arborea indicate that CYCL genes participate in perianth and MMS differentiation processes and do not support a CYCL gene function in initial flower monosymmetry formation. Heterologous CYCL and CYC2 gene overexpression studies in Arabidopsis show that Aristolochia CYCL proteins only perform a CYC2-like function when the CYCL TCP domain is replaced by a CYC2 domain. Comparative TCP domain analyses revealed that an LxxLL motif, known to mediate protein-protein interactions, evolved in the second helix of the TCP domain in the CYC2 lineage and contributes to CYC2-related functions. Our data imply that divergent evolution of the CYC/TB1 lineages caused significant changes in their coding regions, which together with cis-regulatory changes established the key CYC2 function in regulating eudicot flower monosymmetry.

Genome-Wide Identification of TCP Family Transcription Factors in Medicago truncatula Reveals Significant Roles of miR319-Targeted TCPs in Nodule Development

TCP proteins, the plant-specific transcription factors, are involved in the regulation of multiple aspects of plant development among different species, such as leaf development, branching, and flower symmetry. However, thus far, the roles of TCPs in legume, especially in nodulation are still not clear. In this study, a genome-wide analysis of TCP genes was carried out to discover their evolution and function in Medicago truncatula. In total, 21 MtTCPs were identified and classified into class I and class II, and the class II MtTCPs were further divided into two subclasses, CIN and CYC/TB1. The expression profiles of MtTCPs are dramatically different. The universal expression of class I MtTCPs was detected in all organs. However, the MtTCPs in CIN subclass were highly expressed in leaf and most of the members in CYC/TB1 subclass were highly expressed in flower. Such organ-specific expression patterns of MtTCPs suggest their different roles in plant development. In addition, most MtTCPs were down-regulated during the nodule development, except for the putative MtmiR319 targets, MtTCP3, MtTCP4, and MtTCP10A. Overexpression of MtmiR319A significantly reduced the expression level of MtTCP3/4/10A/10B and resulted in the decreased nodule number, indicating the important roles of MtmiR319-targeted MtTCPs in nodulation. Taken together, this study systematically analyzes the MtTCP gene family at a genome-wide level and their possible functions in nodulation, which lay the basis for further explorations of MtmiR319/MtTCPs module in association with nodule development in M. truncatula.

Role of microRNA319 in creeping bentgrass salinity and drought stress response

The microRNA319 family (miR319) is one of the most conserved and ancient microRNA (miRNA) families in plants. Transgenic creeping bentgrass (Agrostis stolonifera) overexpressing a rice miR319, Osa-miR319a, exhibited enhanced salt and drought tolerance. A comprehensive hypothetical model about the role of miR319 in creeping bentgrass response to salinity and drought stress was proposed. Salinity and drought stress induces elevated expression of miR319, resulting in downregulation of at least 4 putative target genes of miR319 (AsPCF5, AsPCF6, AsPCF8, and AsTCP14) as well as a homolog of the rice NAC domain gene AsNAC60, and therefore positively contributing to plant abiotic stress response. Hormones might also regulate miR319 and its targets, and the expression level of the miR319 targets might be a balance of miR319-mediated target cleavage and hormone regulation of the targets. Furthermore, HKT gene families involved in salt exclusion mechanisms as well as mechanisms controlling the timing of gene expression network are also hypothesized to play an important role in this pathway.

Genome-Wide Identification, Characterization and Expression Analysis of the TCP Gene Family in Prunus mume

TCP proteins, belonging to a plant-specific transcription factors family, are known to have great functions in plant development, especially flower and leaf development. However, there is little information about this gene family in Prunus mume, which is widely cultivated in China as an ornamental and fruit tree. Here a genome-wide analysis of TCP genes was performed to explore their evolution in P. mume. Nineteen PmTCPs were identified and three of them contained putative miR319 target sites. Phylogenetic and comprehensive bioinformatics analyses of these genes revealed that different types of TCP genes had undergone different evolutionary processes and the genes in the same clade had similar chromosomal location, gene structure, and conserved domains. Expression analysis of these PmTCPs indicated that there were diverse expression patterns among different clades. Most TCP genes were predominantly expressed in flower, leaf, and stem, and showed high expression levels in the different stages of flower bud differentiation, especially in petal formation stage and gametophyte development. Genes in TCP-P subfamily had main roles in both flower development and gametophyte development. The CIN genes in double petal cultivars might have key roles in the formation of petal, while they were correlated with gametophyte development in the single petal cultivar. The CYC/TB1 type genes were highly detected in the formation of petal and pistil. The less-complex flower types of P. mume might result from the fact that there were only two CYC type genes present in P. mume and a lack of CYC2 genes to control the identity of flower types. These results lay the foundation for further study on the functions of TCP genes during flower development.

Role of TCP Gene BRANCHED1 in the Control of Shoot Branching in Arabidopsis

Branching patterns are major determinants of plant architecture. They depend both on leaf phillotaxy (branch primordia are formed in the axils of leaves) and on the decision of buds to grow out to give a branch or to remain dormant. In Arabidopsis, several genes involved in the long-distance signalling of the control of branch outgrowth have been identified. However, the genes acting inside the buds to cause growth arrest remained unknown until now. In the February issue of Plant Cell we have described the function of BRANCHED1 (BRC1), an Arabidopsis gene coding for a plant-specific transcription factor of the TCP family that is expressed in the buds and prevents their development. Loss of BRC1 function leads to accelerated AM initiation, precocious progression of bud development and excess of shoot branching. BRC1 transcription is affected by endogenous and environmental signals controlling branching and we have shown that BRC1 function mediates the response to these stimuli. Therefore we have proposed that BRC1 function represents the point at which signals controlling branching are integrated within axillary buds.

Genome-Wide Identification and Characterization of the TCP Gene Family in Cucumber (Cucumis sativus L.) and Their Transcriptional Responses to Different Treatments

TCP proteins are plant-specific transcription factors widely implicated in leaf morphogenesis and senescence, flowering, lateral branching, hormone crosstalk, and stress responses. However, the relationship between the transcription pattern of TCPs and organ development in cucumber has not been systematically studied. In this study, we performed a genome-wide identification of putative TCP genes and analyzed their chromosomal location, gene structure, conserved motif, and transcript expression. A total of 27 putative TCP genes were identified and characterized in cucumber. All 27 putative CsTCP genes were classified into class I and class II. Class I comprised 12 CsTCPs and Class II contained 15 CsTCPs. The 27 putative CsTCP genes were randomly distributed in five of seven chromosomes in cucumber. Four putative CsTCP genes were found to contain putative miR319 target sites. Quantitative RT-PCR revealed that 27 putative CsTCP genes exhibited different expression patterns in cucumber tissues and floral organ development. Transcript expression and phenotype analysis showed that the putative CsTCP genes responded to temperature and photoperiod and were induced by gibberellin (GA)and ethylene treatment, which suggested that CsTCP genes may regulate the lateral branching by involving in multiple signal pathways. These results lay the foundation for studying the function of cucumber TCP genes in the future.

Identification, Characterization, and Expression Patterns of TCP Genes and microRNA319 in Cotton

The TEOSINTE BRANCHED 1, CYCLOIDEA, and PROLIFERATING CELL FACTORS (TCP) gene family is a group of plant-specific transcription factors that have versatile functions in developmental processes and stress responses. In this study, a total of 73 TCP genes in upland cotton were identified and characterizated. Phylogenetic analysis classified them into three subgroups: 50 belonged to PCF, 16 to CIN, and 7 to CYC/TB1. GhTCP genes are randomly distributed in 22 of the 26 chromosomes in cotton. Expression patterns of GhTCPs were analyzed in 10 tissues, including different developmental stages of ovule and fiber, as well as under heat, salt, and drought stresses. Transcriptome analysis showed that 44 GhTCP genes exhibited varied transcript accumulation patterns in the tested tissues and 41 GhTCP genes were differentially expressed in response to heat, salt, and drought stresses. Furthermore, three GhTCP genes of the CIN clade were found to contain miR319-binding sites. An anti-correlation expression of GhTCP21 and GhTCP54 was analyzed with miR319 under salt and drought stress. Our results lay the foundation for understanding the complex mechanisms of GhTCP-mediated developmental processes and abiotic stress-signaling transduction pathways in cotton.

Comparative genomic investigation of TCP gene family in eggplant (Solanum melongena L.) and expression analysis under divergent treatments

The putative TCP genes and their responses to abiotic stress in eggplant were comprehensively characterized, and SmTCP genes (Smechr0202855.1 and Smechr0602431.1) may be involved in anthocyanin synthesis. The Teosinte branched1/Cycloidea/Proliferating cell factors (TCPs), a family of plant-specific transcription factors, plays paramount roles in a plethora of developmental and physiological processes. We here systematically characterized putative TCP genes and their response to abiotic stress in eggplant. In total, 30 SmTCP genes were categorized into two subfamilies based on the classical TCP conserved domains. Chromosomal location analysis illustrated the random distribution of putative SmTCP genes along 12 eggplant chromosomes. Cis-acting elements and miRNA target prediction suggested that versatile and complicated regulatory mechanisms that control SmTCPs gene expression, and 3 miRNAs (miR319a, miR319b, and miR319c-3p) might act as major regulators targeting SmTCPs. Tissue expression profiles indicated divergent spatiotemporal expression patterns of SmTCPs. qRT-PCR assays demonstrated different expression profiles of SmTCP under 4 °C, drought and ABA treatment conditions, suggesting the possible participation of SmTCP genes in multiple signaling pathways. Furthermore, RNA-seq data of eggplant anthocyanin synthesis coupled with yeast one-hybrid and dual-luciferase assays suggested the involvement of SmTCP genes (Smechr0202855.1 and Smechr0602431.1) in the mediation of anthocyanin synthesis. Our study will facilitate further investigation on the putative functional characterization of eggplant TCP genes and lay a solid foundation for the in-depth study of the involvement of SmTCP genes in the regulation of anthocyanin synthesis.

Comparative Genomic Analysis of TCP Genes in Six Rosaceae Species and Expression Pattern Analysis in Pyrus bretschneideri

TCP is a plant-specific transcription factor that plays an important role in flowering, leaf development and other physiological processes. In this study, we identified a total of 155 TCP genes: 34 in Pyrus bretschneideri, 19 in Fragaria vesca, 52 in Malus domestica, 19 in Prunus mume, 17 in Rubus occidentalis and 14 in Prunus avium. The evolutionary relationship of the TCP gene family was examined by constructing a phylogenetic tree, tracking gene duplication events, performing a sliding window analysis. The expression profile analysis and qRT-PCR results of different tissues showed that PbTCP10 were highly expressed in the flowers. These results indicated that PbTCP10 might participated in flowering induction in pear. Expression pattern analysis of different developmental stages showed that PbTCP14 and PbTCP15 were similar to the accumulation pattern of fruit lignin and the stone cell content. These two genes might participate in the thickening of the secondary wall during the formation of stone cells in pear. Subcellular localization showed that PbTCPs worked in the nucleus. This study explored the evolution of TCP genes in six Rosaceae species, and the expression pattern of TCP genes in different tissues of “Dangshan Su” pear. Candidate genes related to flower induction and stone cell formation were identified. In summary, our research provided an important theoretical basis for improving pear fruit quality and increasing fruit yield by molecular breeding.

Genome-Wide Identification and Expression Analysis of the TCP Gene Family Related to Developmental and Abiotic Stress in Ginger

Ginger (Zingiber officinale Roscoe), a widely consumed edible and medicinal plant, possesses significant nutritional and economic value. Abiotic stresses such as drought and low temperatures can impact the growth and development of ginger. The plant-specific transcription factor Teosinte branched1/cycloidea/proliferating cell factor (TCP) has progressively been identified in various plants for its role in regulating plant growth and development as well as conferring resistance to abiotic stresses. However, limited information on the TCP family is available in ginger. In this study, we identified 20 TCP members in the ginger genome, which were randomly distributed across 9 chromosomes. Based on phylogenetic analysis, these ginger TCP were classified into two subfamilies: Class I (PCF) and Class II (CIN, CYC/TB). The classification of the identified ginger TCPs was supported by a multi-species phylogenetic tree and motif structure analysis, suggesting that the amplification of the ginger TCP gene family occurred prior to the differentiation of angiosperms. The promoter region of ginger TCP genes was found to contain numerous cis-acting elements associated with plant growth, development, and abiotic stress response. Among these elements, the stress response element, anaerobic induction, and MYB binding site play a dominant role in drought responsiveness. Additionally, expression pattern analysis revealed variations in the expression of ginger TCP gene among different tissues and in response to diverse abiotic stresses (drought, low temperature, heat, and salt). Our research offers a thorough examination of TCP members within the ginger plant. This analysis greatly contributes to the understanding of how TCP genes regulate tissue development and response to stress, opening up new avenues for further exploration in this field.

Unraveling the Developmental and Genetic Mechanisms Underpinning Floral Architecture in Proteaceae

Proteaceae are a basal eudicot family with a highly conserved floral groundplan but which displays considerable variation in other aspects of floral and inflorescence morphology. Their morphological diversity and phylogenetic position make them good candidates for understanding the evolution of floral architecture, in particular the question of the homology of the undifferentiated perianth with the differentiated perianth of core eudicots, and the mechanisms underlying the repeated evolution of zygomorphy. In this paper, we combine a morphological approach to explore floral ontogenesis and a transcriptomic approach to access the genes involved in floral organ identity and development, focusing on Grevillea juniperina, a species from subfamily Grevilleoideae. We present developmental data for Grevillea juniperina and three additional species that differ in their floral symmetry using stereomicroscopy, SEM and High Resolution X-Ray Computed Tomography. We find that the adnation of stamens to tepals takes place at early developmental stages, and that the establishment of bilateral symmetry coincides with the asymmetrical growth of the single carpel. To set a framework for understanding the genetic basis of floral development in Proteaceae, we generated and annotated de novo a reference leaf/flower transcriptome from Grevillea juniperina. We found Grevillea homologs of all lineages of MADS-box genes involved in floral organ identity. Using Arabidopsis thaliana gene expression data as a reference, we found homologs of other genes involved in floral development in the transcriptome of G. juniperina. We also found at least 21 class I and class II TCP genes, a gene family involved in the regulation of growth processes, including floral symmetry. The expression patterns of a set of floral genes obtained from the transcriptome were characterized during floral development to assess their organ specificity and asymmetry of expression.

Inhibition of Arabidopsis thaliana CIN-like TCP transcription factors by Agrobacterium T-DNA-encoded 6B proteins

Agrobacterium T-DNA-encoded 6B proteins cause remarkable growth effects in plants. Nicotiana otophora carries two cellular T-DNAs with three slightly divergent 6b genes (TE-1-6b-L, TE-1-6b-R and TE-2-6b) originating from a natural transformation event. In Arabidopsis thaliana, expression of 2×35S:TE-2-6b, but not 2×35S:TE-1-6b-L or 2×35S:TE-1-6b-R, led to plants with crinkly leaves, which strongly resembled mutants of the miR319a/TCP module. This module is composed of MIR319A and five CIN-like TCP (TEOSINTHE BRANCHED1, CYCLOIDEA and PROLIFERATING CELL NUCLEAR ANTIGEN BINDING FACTOR) genes (TCP2, TCP3, TCP4, TCP10 and TCP24) targeted by miR319a. The CIN-like TCP genes encode transcription factors and are required for cell division arrest at leaf margins during development. MIR319A overexpression causes excessive growth and crinkly leaves. TE-2-6b plants did not show increased miR319a levels, but the mRNA levels of the TCP4 target gene LOX2 were decreased, as in jaw-D plants. Co-expression of green fluorescent protein (GFP)-tagged TCPs with native or red fluorescent protein (RFP)-tagged TE-6B proteins led to an increase in TCP protein levels and formation of numerous cytoplasmic dots containing 6B and TCP proteins. Yeast double-hybrid experiments confirmed 6B/TCP binding and showed that TE-1-6B-L and TE-1-6B-R bind a smaller set of TCP proteins than TE-2-6B. A single nucleotide mutation in TE-1-6B-R enlarged its TCP-binding repertoire to that of TE-2-6B and caused a crinkly phenotype in Arabidopsis. Deletion analysis showed that TE-2-6B targets the TCP4 DNA-binding domain and directly interferes with transcriptional activation. Taken together, these results provide detailed insights into the mechanism of action of the N. otophora TE-encoded 6b genes.