A common miRNA160-based mechanism regulates ovary patterning, floral organ abscission and lamina outgrowth in tomato

microRNA regulates cytokinin induced parthenocarpy in cucumber (Cucumis sativus L.)

Parthenocarpy is one of the most important agronomic traits for fruit yield in cucumbers. However, the precise gene regulation and the posttranscriptional mechanism are elusive. In the presented study, one parthenocarpic line DDX and non-parthenocarpic line ZK were applied to identify the microRNAs (miRNAs) involved in parthenocarpic fruit formation. The differential expressed miRNAs among parthenocarpic fruit of forchlorfenuron (CPPU) treated ZK (ZK-CPPU), pollinated ZK (ZK-P), non-pollinated DDX (DDX-NP) were compared with the non-parthenocarpic fruits of non-pollinated ZK (ZK-NP). It indicated 98 miRNAs exhibited differential expression were identified. Notably, a significant proportion of these miRNAs were enriched in the signal transduction pathway of plant hormones, as identified by the KEGG pathway analysis. qRT-PCR validation indicated that CsmiR156 family was upregulated in the ZK-NP while downregulated in ZK-CPPU, ZK-P, and DDX-NP at 1 day after anthesis. Meanwhile, the opposite trend was observed for CsmiR164a. In ZK-CPPU, ZK-P, and DDX-NP, CsmiRNA156 genes (CsSPL16 and CsARR9-like) were upregulated while CsmiRNA164a genes (CsNAC6, CsCUC1, and CsNAC100) were downregulated. The GUS and dual luciferase assay validated that CsmiR156a inhibited while CsmiR164a induced their target genes' transcription. This study presents novel insights into the involvement of CsmiR156a and CsmiR164a in the CK-mediated posttranscriptional regulation of cucumber parthenocarpy, which will aid future breeding programs.

Genomic survey and expression analysis of LcARFs reveal multiple functions to somatic embryogenesis in Liriodendron

BACKGROUND

Auxin response factors (ARFs) are critical transcription factors that mediate the auxin signaling pathway and are essential for regulating plant growth. However, there is a lack of understanding regarding the ARF gene family in Liriodendron chinense, a vital species in landscaping and economics. Thus, further research is needed to explore the roles of ARFs in L. chinense and their potential applications in plant development.

RESULT

In this study, we have identified 20 LcARF genes that belong to three subfamilies in the genome of L. chinense. The analysis of their conserved domains, gene structure, and phylogeny suggests that LcARFs may be evolutionarily conserved and functionally similar to other plant ARFs. The expression of LcARFs varies in different tissues. Additionally, they are also involved in different developmental stages of somatic embryogenesis. Overexpression of LcARF1, LcARF2a, and LcARF5 led to increased activity within callus. Additionally, our promoter-GFP fusion study indicated that LcARF1 may play a role in embryogenesis. Overall, this study provides insights into the functions of LcARFs in plant development and embryogenesis, which could facilitate the improvement of somatic embryogenesis in L. chinense.

CONCLUSION

The research findings presented in this study shed light on the regulatory roles of LcARFs in somatic embryogenesis in L. chinense and may aid in accelerating the breeding process of this tree species. By identifying the specific LcARFs involved in different stages of somatic embryogenesis, this study provides a basis for developing targeted breeding strategies aimed at optimizing somatic embryogenesis in L. chinense, which holds great potential for improving the growth and productivity of this economically important species.

Role of microRNAs and their putative mechanism in regulating potato (Solanum tuberosum L.) life cycle and response to various environmental stresses

The exponentially increasing population and the demand for food is inextricably linked. This has shifted global attention to improving crop plant traits to meet global food demands. Potato (Solanum tuberosum L.) is a major non-grain food crop that is grown all over the world. Currently, some of the major global potato research work focuses on the significance of microRNAs (miRNAs) in potato. miRNAs are a type of non-coding RNAs that regulate the gene expression of their target mRNA genes by cleavage and/or their translational inhibition. This suggests an essential role of miRNAs in a multitude of plant biological processes, including maintenance of genome integrity, plant growth, development and maturation, and initiation of responses to various stress conditions. Therefore, engineering miRNAs to generate stress-resistant varieties of potato may result in high yield and improved nutritional qualities. In this review, we discuss the potato miRNAs specifically known to play an essential role in the various stages of the potato life cycle, conferring stress-resistant characteristics, and modifying gene expression. This review highlights the significance of the miRNA machinery in plants, especially potato, encouraging further research into engineering miRNAs to boost crop yields and tolerance towards stress.

FvemiR160-FveARF18A-FveAP1/FveFUL module regulates flowering time in woodland strawberry

Flowering is an indicator of plant transformation from vegetative to reproductive growth. miR160 has been shown to have a significant effect on the growth and development of fruits, leaves, and roots of plants or their stress response to environment, but the participation of miR160 in regulating flowering time in plants is unclear. In this study, we found that two FvemiR160s (FvemiR160a/FvemiR160b) mature sequences in strawberry (Fragaria vesca) were consistent. It was displayed that the miR160 mature sequence is highly conserved in various species, and the miR160 mature sequence formed by the 5' arm of the MIR160 precursor was more conserved. Three FveARFs in woodland strawberry were negatively regulated by FvemiR160a, among which FveARF18A was the most significant. Phylogenetic analysis indicated that FvemiR160 is closely related to apple (Malus domestica), grape (Vitis vinifera), and Arabidopsis thaliana, while FveARF18A is closely related to RcARF18. Subsequently, we demonstrated that FvemiR160a can target cutting FveARF18A to negatively regulate its expression by RLM-5' RACE, cleavage site mutation, and GFP fluorescence assay. Moreover, we observed that FveMIR160a overexpressed plants have advanced flowering, while mFveARF18A overexpressed plants have delayed flowering. We also verified that FveARF18A negatively regulates the expression of FveAP1 and FveFUL by binding their promoters by yeast one-hybrid, LUC, and GUS assay, and FveAP1 and FveFUL transgenic Arabidopsis showed early flowering phenotype. In addition, the expression level of FvemiR160a was decreased obviously while that of FveARF18A was increased obviously by MeJA, GA and IAA. In conclusion, our study reveals the important role of the FvemiR160-FveARF18A-FveAP1/FveFUL module in the flowering process of woodland strawberry and provides a new pathway for studying flowering.

Auxin homeostasis is maintained by sly-miR167-SlARF8A/B-SlGH3.4 feedback module in the development of locular and placental tissues of tomato fruits

The locular gel, produced by the placenta, is important for fruit flavor and seed development in tomato. However, the mechanism underlying locule and placenta development is not fully understood yet. Here, we show that two SlARF transcription factors, SlARF8B and SlARF8A (SlARF8A/B), promote the development of locular and placenta tissues. The expression of both SlARF8A and SlARF8B is repressed by sly-microRNA167 (sly-miR167), allowing for the activation of auxin downstream genes. In slarf8a, slarf8b, and slarf8a/b mutants, the auxin (IAA) levels are decreased, whereas the levels of inactive IAA conjugates including IAA-Ala, IAA-Asp, and IAA-Glu are increased. We further find that SlARF8B directly inhibits the expression of SlGH3.4, an acyl acid amino synthetase that conjugates the amino acids to IAA. Disruption of such auxin balance by the increased expression of SlGH3.4 or SlGH3.2 results in defective locular and placental tissues. Taken together, our findings reveal an important regulatory module constituted by sly-miR167-SlARF8A/B-SlGH3.4 during the development of locular and placenta tissues of tomato fruits.

bra-miR167a Targets ARF8 and Negatively Regulates Arabidopsis thaliana Immunity against Plasmodiophora brassicae

Clubroot is a soil-borne disease caused by Plasmodiophora brassicae, which can seriously affect the growth and production of cruciferous crops, especially Chinese cabbage crops, worldwide. At present, few studies have been conducted on the molecular mechanism of this disease's resistance response. In this experiment, we analyzed the bioinformation of bra-miR167a, constructed a silencing vector (STTM167a) and an overexpression vector (OE-miR167a), and transformed them to Arabidopsis to confirm the role of miR167a in the clubroot resistance mechanism of Arabidopsis. Afterwards, phenotype analysis and expression level analysis of key genes were conducted on transgenic plants. From the result, we found that the length and number of lateral roots of silence transgenic Arabidopsis STTM167a was higher than that of WT and OE-miR167a. In addition, the STTM167a transgenic Arabidopsis induced up-regulation of disease resistance-related genes (PR1, PR5, MPK3, and MPK6) at 3 days after inoculation. On the other hand, the auxin pathway genes (TIR1, AFB2, and AFB3), which are involved in maintaining the balance of auxin/IAA and auxin response factor (ARF), were down-regulated. These results indicate that bra-miR167a is negative to the development of lateral roots and auxins, but positive to the expression of resistance-related genes. This also means that the STTM167a can improve the resistance of clubroot by promoting lateral root development and the level of auxin, and can induce resistance-related genes by regulating its target genes. We found a positive correlation between miR167a and clubroot disease, which is a new clue for the prevention and treatment of clubroot disease.

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.

The Impact of Tobamovirus Infection on Root Development Involves Induction of Auxin Response Factor 10a in Tomato

Plant viruses cause systemic diseases that severely impair plant growth and development. While the accumulation of viruses in the root system has long been established, little is known as to how viruses affect root architecture. Here, we examined how the emerging tobamovirus, tomato brown rugose fruit virus (ToBRFV), alters root development in tomato. We found that ToBRFV and tobacco mosaic virus both invaded root systems during the first week of infection. ToBRFV infection of tomato plants resulted in a significant decrease in root biomass and elongation and root-to-shoot ratio and a marked suppression of root branching. Mutation in RNA-dependent RNA polymerase 6 increased the susceptibility of tomato plants to ToBRFV, resulting in severe reduction of various root growth parameters including root branching. Viral root symptoms were associated with the accumulation of auxin response factor 10a (SlARF10a) transcript, a homolog of Arabidopsis ARF10, a known suppressor of lateral root development. Interestingly, loss-of-function mutation in SlARF10a moderated the effect of ToBRFV on root branching. In contrast, downregulation of sly-miR160a, which targets SlARF10a, was associated with constitutive suppression root branching independent of viral infection. In addition, overexpression of a microRNA-insensitive mutant of SlARF10a mimicked the effect of ToBRFV on root development, suggesting a specific role for SlARF10a in ToBRFV-mediated suppression of root branching. Taken together, our results provide new insights into the impact of tobamoviruses on root development and the role of ARF10a in the suppression of root branching in tomato.

Coordinating Diverse Functions of miRNA and lncRNA in Fleshy Fruit

Non-coding RNAs play vital roles in the diverse biological processes of plants, and they are becoming key topics in horticulture research. In particular, miRNAs and long non-coding RNAs (lncRNAs) are receiving increased attention in fruit crops. Recent studies in horticulture research provide both genetic and molecular evidence that miRNAs and lncRNAs regulate biological function and stress responses during fruit development. Here, we summarize multiple regulatory modules of miRNAs and lncRNAs and their biological roles in fruit sets and stress responses, which would guide the development of molecular breeding techniques on horticultural crops.

Understanding the molecular mechanism of leaf morphogenesis in vegetable crops conduces to breeding process

Leaf morphology can affect the development and yield of plants by regulating plant architecture and photosynthesis. Several factors can determine the final leaf morphology, including the leaf complexity, size, shape, and margin type, which suggests that leaf morphogenesis is a complex regulation network. The formation of diverse leaf morphology is precisely controlled by gene regulation on translation and transcription levels. To further reveal this, more and more genome data has been published for different kinds of vegetable crops and advanced genotyping approaches have also been applied to identify the causal genes for the target traits. Therefore, the studies on the molecular regulation of leaf morphogenesis in vegetable crops have also been largely improved. This review will summarize the progress on identified genes or regulatory mechanisms of leaf morphogenesis and development in vegetable crops. These identified markers can be applied for further molecular-assisted selection (MAS) in vegetable crops. Overall, the review will contribute to understanding the leaf morphology of different crops from the perspective of molecular regulation and shortening the breeding cycle for vegetable crops.

FveARF2 negatively regulates fruit ripening and quality in strawberry

Auxin response factors (ARFs) are transcription factors that play important roles in plants. ARF2 is a member of the ARF family and participates in many plant growth and developmental processes. However, the role of ARF2 in strawberry fruit quality remains unclear. In this study, FveARF2 was isolated from the woodland strawberry 'Ruegen' using reverse transcription-polymerase chain reaction (RT-PCR), which showed that FveARF2 expression levels were higher in the stem than in other organs of the 'Ruegen' strawberry. Moreover, FaARF2 was higher in the white fruit stage of cultivated strawberry fruit than in other stage. Subcellular localization analysis showed that FveARF2 is located in the nucleus, while transcriptional activation assays showed that FveARF2 inhibited transcription in yeast. Silencing FveARF2 in cultivated strawberry fruit revealed earlier coloration and higher soluble solid, sugar, and anthocyanin content in the transgenic fruit than in the control fruit, overexpression of FveARF2 in strawberry fruit delayed ripening and lower soluble solid, sugar, and anthocyanin content compared to the control fruit. Gene expression analysis indicated that the transcription levels of the fruit ripening genes FaSUT1, FaOMT, and FaCHS increased in FveARF2-RNAi fruit and decreased in FveARF2-OE fruit, when compared with the control. Furthermore, yeast one-hybrid (Y1H) and GUS activity experiments showed that FveARF2 can directly bind to the AuxRE (TGTCTC) element in the FaSUT1, FaOMT, and FaCHS promoters in vitro and in vivo. Potassium ion supplementation improved the quality of strawberry fruit, while silencing FveARF2 increased potassium ion content in transgenic fruit. The Y1H and GUS activity experiments also confirmed that FveARF2 could directly bind to the promoter of FveKT12, a potassium transporter gene, and inhibited its expression. Taken together, we found that FveARF2 can negatively regulate strawberry fruit ripening and quality, which provides new insight for further study of the molecular mechanism of strawberry fruit ripening.

Tomato MicroRNAs and Their Functions

MicroRNAs (miRNAs) define an essential class of non-coding small RNAs that function as posttranscriptional modulators of gene expression. They are coded by MIR genes, several hundreds of which exist in the genomes of Arabidopsis and rice model plants. The functional analysis of Arabidopsis and rice miRNAs indicate that their miRNAs regulate a wide range of processes including development, reproduction, metabolism, and stress. Tomato serves as a major model crop for the study of fleshy fruit development and ripening but until recently, information on the identity of its MIR genes and their coded miRNAs was limited and occasionally contradictory. As a result, the majority of tomato miRNAs remained uncharacterized. Recently, a comprehensive annotation of tomato MIR genes has been carried out by several labs and us. In this review, we curate and organize the resulting partially overlapping MIR annotations into an exhaustive and non-redundant atlas of tomato MIR genes. There are 538 candidate and validated MIR genes in the atlas, of which, 169, 18, and 351 code for highly conserved, Solanaceae-specific, and tomato-specific miRNAs, respectively. Furthermore, a critical review of functional studies on tomato miRNAs is presented, highlighting validated and possible functions, creating a useful resource for future tomato miRNA research.

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.

miR3633a-GA3ox2 Module Conducts Grape Seed-Embryo Abortion in Response to Gibberellin

Seedlessness is one of the important quality and economic traits favored by grapevine consumers, which are mainly affected by phytohormones, especially gibberellin (GA). GA is widely utilized in seedless berry production and could effectively induce grape seed embryo abortion. However, the molecular mechanism underlying this process, like the role of RNA silencing in the biosynthesis pathway of GA remains elusive. Here, Gibberellin 3-β dioxygenase2 (GA3ox2) as the last key enzyme in GA biosynthesis was predicated as a potential target gene for miR3633a, and two of them were identified as a GA response in grape berries. We also analyzed the promoter regions of genes encoding GA biosynthesis and found the hormone-responsive elements to regulate grape growth and development. The cleavage interaction between VvmiR3633a and VvGA3ox2 was validated by RLM-RACE and the transient co-transformation technique in tobacco in vivo. Interestingly, during GA-induced grape seed embryo abortion, exogenous GA promoted the expression of VvmiR3633a, thereby mainly repressing the level of VvGA3ox2 in seed embryos. We also observed a negative correlation between down-regulated VvGA20ox2/VvGA3ox2 and up-regulated VvGA2ox3/VvGA2ox1, of which GA inactivation was greater than GA synthesis, inhibited active GA content, accompanied by the reduction of VvSOD and VvCAT expression levels and enzymatic activities. These series of changes might be the main causes of grape seed embryo abortion. In conclusion, we have preliminarily drawn a schematic mode of GA-mediated VvmiR3633a and related genes regulatory network during grape seed abortion induced by exogenous GA. Our findings provide novel insights into the GA-responsive roles of the VvmiR3633a-VvGA3ox2 module in the modulation of grape seed-embryo abortion, which has implications for the molecular breeding of high-quality seedless grape berries.

Pivotal Role of Phytohormones and Their Responsive Genes in Plant Growth and Their Signaling and Transduction Pathway under Salt Stress in Cotton

The presence of phyto-hormones in plants at relatively low concentrations plays an indispensable role in regulating crop growth and yield. Salt stress is one of the major abiotic stresses limiting cotton production. It has been reported that exogenous phyto-hormones are involved in various plant defense systems against salt stress. Recently, different studies revealed the pivotal performance of hormones in regulating cotton growth and yield. However, a comprehensive understanding of these exogenous hormones, which regulate cotton growth and yield under salt stress, is lacking. In this review, we focused on new advances in elucidating the roles of exogenous hormones (gibberellin (GA) and salicylic acid (SA)) and their signaling and transduction pathways and the cross-talk between GA and SA in regulating crop growth and development under salt stress. In this review, we not only focused on the role of phyto-hormones but also identified the roles of GA and SA responsive genes to salt stress. Our aim is to provide a comprehensive review of the performance of GA and SA and their responsive genes under salt stress, assisting in the further elucidation of the mechanism that plant hormones use to regulate growth and yield under salt stress.

Genome–Wide Identification and Functional Characterization of Auxin Response Factor (ARF) Genes in Eggplant

Auxin response factors (ARFs) are important plant transcription factors that are differentially expressed in response to auxin and various abiotic stresses. ARFs play important roles in mediating plant growth and stress responses; however, these factors have not been studied in eggplants. In this study, genome–wide identification and the functional analysis of the ARF gene family in eggplants (Solanum melongena L.) were performed. A total of 20 ARF (SmARF) genes were identified and phylogenetically classified into three groups. Our analysis revealed four functional domains and 10 motifs in these proteins. Subcellular localization showed that the SmARFs localized in the nucleus. To investigate the biological functions of the SmARFs under 2,4–D and salt stress treatments, quantitative real–time RT–PCR (qRT–PCR) was conducted. Most SmARF genes exhibited changes in expression in response to 2,4–D treatments in the flowers, especially SmARF4 and 7B. All SmARF genes quickly responded to salt stress, except SmARF17 and 19 in leaves, SmARF1A and 7B in roots, and SmARF2A, SmARF7B, and SmARF16B in stems. These results helped to elucidate the role of ARFs in auxin signaling under 2,4–D and salt stress in eggplants.

Sly-miR159 regulates fruit morphology by modulating GA biosynthesis in tomato

Fruit morphology is an important agronomical trait of many crops. Here, we identify Sly-miR159 as an important regulator of fruit morphology in tomato, a model species of fleshy-fruit development. We show that Sly-miR159 functions through its target SlGAMYB2 to control fruit growth. Suppression of Sly-miR159 and overexpression of SlGAMYB2 result in larger fruits with a reduced length/width ratio, while loss of function of SlGAMYB2 leads to the formation of smaller and more elongated fruits. Gibberellin (GA) is a major phytohormone that regulates fruit development in tomato. We show the Sly-miR159-SlGAMYB2 pathway controls fruit morphology by modulating GA biosynthesis. In particular, we demonstrate that Sly-miR159 promotes GA biosynthesis largely through the direct repression of the GA biosynthetic gene SlGA3ox2 by SlGAMYB2. Together, our findings reveal the action of Sly-miR159 on GA biosynthesis as a previously unidentified mechanism that controls fruit morphology in tomato. Modulating this pathway may have potential applications in tomato breeding for manipulating fruit growth and facilitating the process of fruit improvement.

AUXIN RESPONSE FACTOR 16 (StARF16) regulates defense gene StNPR1 upon infection with necrotrophic pathogen in potato

We demonstrate a new regulatory mechanism in the jasmonic acid (JA) and salicylic acid (SA) mediated crosstalk in potato defense response, wherein, miR160 target StARF16 (a gene involved in growth and development) binds to the promoter of StNPR1 (a defense gene) and negatively regulates its expression to suppress the SA pathway. Overall, our study establishes the importance of StARF16 in regulation of StNPR1 during JA mediated defense response upon necrotrophic pathogen interaction. Plants employ antagonistic crosstalk between salicylic acid (SA) and jasmonic acid (JA) to effectively defend them from pathogens. During biotrophic pathogen attack, SA pathway activates and suppresses the JA pathway via NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1). However, upon necrotrophic pathogen attack, how JA-mediated defense response suppresses the SA pathway, is still not well-understood. Recently StARF10 (AUXIN RESPONSE FACTOR), a miR160 target, has been shown to regulate SA and binds to the promoter of StGH3.6 (GRETCHEN HAGEN3), a gene proposed to maintain the balance between the free SA and auxin in plants. In the current study, we investigated the role of StARF16 (a miR160 target) in the regulation of the defense gene StNPR1 in potato upon activation of the JA pathway. We observed that a negative correlation exists between StNPR1 and StARF16 upon infection with the pathogen. The results were further confirmed through the exogenous application of SA and JA. Using yeast one-hybrid assay, we demonstrated that StARF16 binds to the StNPR1 promoter through putative ARF binding sites. Additionally, through protoplast transfection and chromatin immunoprecipitation experiments, we showed that StARF16 could bind to the StNPR1 promoter and regulate its expression. Co-transfection assays using promoter deletion constructs established that ARF binding sites are present in the 2.6 kb sequence upstream to the StNPR1 gene and play a key role in its regulation during infection. In summary, we demonstrate the importance of StARF16 in the regulation of StNPR1, and thus SA pathway, during JA-mediated defense response upon necrotrophic pathogen interaction.

Advances in the regulation of plant salt-stress tolerance by miRNA

Salt stress significantly affects the growth, development, yield, and quality of plants. MicroRNAs (miRNAs) are involved in various stress responses via target gene regulation. Their role in regulating salt stress has also received significant attention from researchers. Various transcription factor families are the common target genes of plant miRNAs. Thus, regulating the expression of miRNAs is a novel method for developing salt-tolerant crops. This review summarizes plant miRNAs that mediate salt tolerance, specifically miRNAs that have been utilized in genetic engineering to modify plant salinity tolerance. The molecular mechanism by which miRNAs mediate salt stress tolerance merits elucidation, and this knowledge will promote the development of miRNA-mediated salt-tolerant crops and provide new strategies against increasingly severe soil salinization.

ARF6s Identification and Function Analysis Provide Insights Into Flower Development of Punica granatum L

Based on the genome and small-RNA sequencing of pomegranate, miRNA167 and three target genes PgARF6 were identified in "Taishanhong" genome. Three PgARF6 genes and their corresponding protein sequences, expression patterns in pomegranate flower development and under exogenous hormones treatments were systematically analyzed in this paper. We found that PgARF6s are nuclear proteins with conserved structures. However, PgARF6s had different protein structures and expression profiles in pomegranate flower development. At the critical stages of pomegranate ovule sterility (8.1-14.0 mm), the expression levels of PgARF6s in bisexual flowers were lower than those in functional male flowers. Interestingly, PgARF6c expression level was significantly higher than PgARF6a and PgARF6b. Under the treatment of exogenous IBA and 6-BA, PgARF6s were down-regulated, and the expression of PgARF6c was significantly inhibited. PgmiR167a and PgmiR167d had the binding site on PgARF6 genes sequences, and PgARF6a has the directly targeted regulatory relationship with PgmiR167a in pomegranate. At the critical stage of ovule development (8.1-12.0 mm), exogenous IBA and 6-BA promoted the content of GA and ZR accumulation, inhibited BR accumulation. There was a strong correlation between the expression of PgARF6a and PgARF6b. Under exogenous hormone treatment, the content of ZR, BR, GA, and ABA were negatively correlated with the expressions of PgARF6 genes. However, JA was positively correlated with PgARF6a and PgARF6c under IBA treatment. Thus, our results provide new evidence for PgARF6 genes involving in ovule sterility in pomegranate flowers.

MicroRNAs Are Involved in Regulating Plant Development and Stress Response through Fine-Tuning of TIR1/AFB-Dependent Auxin Signaling

Auxin, primarily indole-3-acetic acid (IAA), is a versatile signal molecule that regulates many aspects of plant growth, development, and stress response. Recently, microRNAs (miRNAs), a type of short non-coding RNA, have emerged as master regulators of the auxin response pathways by affecting auxin homeostasis and perception in plants. The combination of these miRNAs and the autoregulation of the auxin signaling pathways, as well as the interaction with other hormones, creates a regulatory network that controls the level of auxin perception and signal transduction to maintain signaling homeostasis. In this review, we will detail the miRNAs involved in auxin signaling to illustrate its in planta complex regulation.

Epigenetics and its role in effecting agronomical traits

Climate-resilient crops with improved adaptation to the changing climate are urgently needed to feed the growing population. Hence, developing high-yielding crop varieties with better agronomic traits is one of the most critical issues in agricultural research. These are vital to enhancing yield as well as resistance to harsh conditions, both of which help farmers over time. The majority of agronomic traits are quantitative and are subject to intricate genetic control, thereby obstructing crop improvement. Plant epibreeding is the utilisation of epigenetic variation for crop development, and has a wide range of applications in the field of crop improvement. Epigenetics refers to changes in gene expression that are heritable and induced by methylation of DNA, post-translational modifications of histones or RNA interference rather than an alteration in the underlying sequence of DNA. The epigenetic modifications influence gene expression by changing the state of chromatin, which underpins plant growth and dictates phenotypic responsiveness for extrinsic and intrinsic inputs. Epigenetic modifications, in addition to DNA sequence variation, improve breeding by giving useful markers. Also, it takes epigenome diversity into account to predict plant performance and increase crop production. In this review, emphasis has been given for summarising the role of epigenetic changes in epibreeding for crop improvement.

miR160: An Indispensable Regulator in Plant

MicroRNAs (miRNA), recognized as crucial regulators of gene expression at the posttranscriptional level, have been found to be involved in the biological processes of plants. Some miRNAs are up- or down-regulated during plant development, stress response, and secondary metabolism. Over the past few years, it has been proved that miR160 is directly related to the developments of different tissues and organs in multifarious species, as well as plant-environment interactions. This review highlights the recent progress on the contributions of the miR160-ARF module to important traits of plants and the role of miR160-centered gene regulatory network in coordinating growth with endogenous and environmental factors. The manipulation of miR160-guided gene regulation may provide a new method to engineer plants with improved adaptability and yield.

Genome-wide identification of auxin response factor (ARF) gene family and the miR160-ARF18-mediated response to salt stress in peanut (Arachis hypogaea L.)

Auxin response factors (ARFs) are transcription factors that regulate the transcription of auxin-responsive genes during plant growth and development. In this study, 29 and 30 ARF members were identified from the two wild peanut species, A. duranensis and A. ipaensis, respectively. The ARFs, including their classifications, conserved domains and evolutionary relationships were characterized. RNA-seq analyses revealed that some of the ARF genes were responsive to abiotic stress, particularly high salinity. In addition to abiotic stress, the expression of 2 ARF members was also regulated by biotic stress, specifically Bradyrhizobium infection in A. duranensis. The ARF gene Arahy.7DXUOK was predicted to be a potential target of miR160. Overexpression of miR160 could cause degradation of the Arahy.7DXUOK target gene transcript and increased salt tolerance in miR160OX transgenic plants. Therefore, these molecular characterization and expression profile analyses provide comprehensive information on ARF family members and will help to elucidate their functions to facilitate further research on peanuts.

Genome-Wide Identification of ARF Gene Family Suggests a Functional Expression Pattern during Fruitlet Abscission in Prunus avium L

Auxin response factors (ARFs) play a vital role in plant growth and development. In the current study, 16 ARF members have been identified in the sweet cherry (Prunus avium L.) genome. These genes are all located in the nucleus. Sequence analysis showed that genes in the same subgroup have similar exon-intron structures. A phylogenetic tree has been divided into five groups. The promoter sequence includes six kinds of plant hormone-related elements, as well as abiotic stress response elements such as low temperature or drought. The expression patterns of PavARF in different tissues, fruitlet abscission, cold and drought treatment were comprehensively analyzed. PavARF10/13 was up-regulated and PavARF4/7/11/12/15 was down-regulated in fruitlet abscising. These genes may be involved in the regulation of fruit drop in sweet cherry fruits. This study comprehensively analyzed the bioinformatics and expression pattern of PavARF, which can lay the foundation for further understanding the PavARF family in plant growth development and fruit abscission.

MicroRNAs in Woody Plants

MicroRNAs (miRNAs) are small (∼21-nucleotides) non-coding RNAs found in plant and animals. MiRNAs function as critical post-transcriptional regulators of gene expression by binding to complementary sequences in their target mRNAs, leading to mRNA destabilization and translational inhibition. Plant miRNAs have some distinct characteristics compared to their animal counterparts, including greater evolutionary conservation and unique miRNA processing methods. The lifecycle of a plant begins with embryogenesis and progresses through seed germination, vegetative growth, reproductive growth, flowering and fruiting, and finally senescence and death. MiRNAs participate in the transformation of plant growth and development and directly monitor progression of these processes and the expression of certain morphological characteristics by regulating transcription factor genes involved in cell growth and differentiation. In woody plants, a large and rapidly increasing number of miRNAs have been identified, but their biological functions are largely unknown. In this review, we summarize the progress of miRNA research in woody plants to date. In particular, we discuss the potential roles of these miRNAs in growth, development, and biotic and abiotic stresses responses in woody plants.

Identification and Expression Analysis of miR160 and Their Target Genes in Cucumber

miR160 plays a crucial role in various biological processes by regulating their target gene auxin response factor (ARF) in plants. However, little is known about miR160 and ARF in cucumber fruit expansion. Here, 4 Csa-MIR160 family members and 17 CsARFs were identified through a genome-wide search. Csa-miR160 showed a closer relationship with those in melon. Phylogenetic analysis revealed that CsARFs were divided into four classes and most of CsARFs presented a closer evolutionary relationship with those from tomato. Putative cis-elements analysis predicted that Csa-MIR160 and CsARFs were involved in light, phytohormone and stress response, which proved that they might take part in light, phytohormone and stress signaling pathway by the miR160-ARF module. In addition, CsARF5, CsARF11, CsARF13 and CsARF14 were predicted as the target genes of Csa-miR160. qRT-PCR revealed that Csa-miR160 and their target gene CsARFs were differentially expressed in differential cucumber tissues and developmental stages. Csa-miR160d was only expressed in the expanded cucumber fruit. CsARF5, CsARF11 and CsARF13 exhibited the lower expression in the expanded fruit than those in the ovary, while, CsARF14 showed the reverse trend. Our results suggested that Csa-miR160d might play a crucial role in cucumber fruit expansion by negatively targeting CsARF5, CsARF11 and CsARF13. This is the first genome-wide analysis of miR160 in cucumber. These findings provide useful information and resources for further studying the role of miR160 and ARF in cucumber fruit expansion.

A prescient evolutionary model for genesis, duplication and differentiation of MIR160 homologs in Brassicaceae

MicroRNA160 is a class of nitrogen-starvation responsive genes which governs establishment of root system architecture by down-regulating AUXIN RESPONSE FACTOR genes (ARF10, ARF16 and ARF17) in plants. The high copy number of MIR160 variants discovered by us from land plants, especially polyploid crop Brassicas, posed questions regarding genesis, duplication, evolution and function. Absence of studies on impact of whole genome and segmental duplication on retention and evolution of MIR160 homologs in descendent plant lineages prompted us to undertake the current study. Herein, we describe ancestry and fate of MIR160 homologs in Brassicaceae in context of polyploidy driven genome re-organization, copy number and differentiation. Paralogy amongst Brassicaceae MIR160a, MIR160b and MIR160c was inferred using phylogenetic analysis of 468 MIR160 homologs from land plants. The evolutionarily distinct MIR160a was found to represent ancestral form and progenitor of MIR160b and MIR160c. Chronology of evolutionary events resulting in origin and diversification of genomic loci containing MIR160 homologs was delineated using derivatives of comparative synteny. A prescient model for causality of segmental duplications in establishment of paralogy in Brassicaceae MIR160, with whole genome duplication accentuating the copy number increase, is being posited in which post-segmental duplication events viz. differential gene fractionation, gene duplications and inversions are shown to drive divergence of chromosome segments. While mutations caused the diversification of MIR160a, MIR160b and MIR160c, duplicated segments containing these diversified genes suffered gene rearrangements via gene loss, duplications and inversions. Yet the topology of phylogenetic and phenetic trees were found congruent suggesting similar evolutionary trajectory. Over 80% of Brassicaceae genomes and subgenomes showed a preferential retention of single copy each of MIR160a, MIR160b and MIR160c suggesting functional relevance. Thus, our study provides a blue-print for reconstructing ancestry and phylogeny of MIRNA gene families at genomics level and analyzing the impact of polyploidy on organismal complexity. Such studies are critical for understanding the molecular basis of agronomic traits and deploying appropriate candidates for crop improvement.

Identification of miRNAs and Their Targets Involved in Flower and Fruit Development across Domesticated and Wild Capsicum Species

MicroRNAs (miRNAs) are regulators of the post-transcription stage of gene activity documented to play central roles in flower and fruit development in model plant species. However, little is known about their roles and differences in domesticated and wild Capsicum species. In this study, we used high-throughput sequencing to analyze the miRNA content at three developmental stages (flower, small fruit, and middle fruit) from two cultivated (C. baccatum and C. annuum) and two wild (C. chacoense and C. eximium) pepper species. This analysis revealed 22 known and 27 novel miRNAs differentially expressed across species and tissues. A number of stage- and species-specific miRNAs were identified, and Gene Ontology terms were assigned to 138 genes targeted by the miRNAs. Most Gene Ontology terms were for the categories "genetic information processing", "signaling and cellular processes", "amino acid metabolism", and "carbohydrate metabolism". Enriched KEGG analysis revealed the pathways amino acids, sugar and nucleotide metabolism, starch and sucrose metabolism, and fructose-mannose metabolism among the principal ones regulated by miRNAs during pepper fruit ripening. We predicted miRNA-target gene interactions regulating flowering time and fruit development, including miR156/157 with SPL genes, miR159 with GaMYB proteins, miR160 with ARF genes, miR172 with AP2-like transcription factors, and miR408 with CLAVATA1 gene across the different Capsicum species. In addition, novel miRNAs play an important role in regulating interactions potentially controlling plant pathogen defense and fruit quality via fructokinase, alpha-L-arabinofuranosidase, and aromatic and neutral amino acid transporter. Overall, the small RNA-sequencing results from this study represent valuable information that provides a solid foundation for uncovering the miRNA-mediated mechanisms of flower and fruit development between domesticated and wild Capsicum species.

SlERF52 regulates SlTIP1;1 expression to accelerate tomato pedicel abscission

Abscission of plant organs is induced by developmental signals and diverse environmental stimuli and involves multiple regulatory networks, including biotic or abiotic stress-impaired auxin flux in the abscission zone (AZ). Depletion of auxin activates AZ ethylene (ETH) production and triggers acceleration of abscission, a process that requires hydrogen peroxide (H2O2). However, the interaction between these networks and the underlying mechanisms that control abscission are poorly understood. Here, we found that expression of tonoplast intrinsic proteins, which belong to the aquaporin (AQP) family in the AZ was important for tomato (Solanum lycopersicum) pedicel abscission. Liquid chromatography-tandem mass spectrometry and in situ hybridization revealed that SlTIP1;1 was most abundant and specifically present in the tomato pedicel AZ. SlTIP1;1 localized in the plasma membrane and tonoplast. Knockout of SlTIP1;1 resulted in delayed abscission, whereas overexpression of SlTIP1;1 accelerated abscission. Further analysis indicated that SlTIP1;1 mediated abscission via gating of cytoplasmic H2O2 concentrations and osmotic water permeability (Pf). Elevated cytoplasmic levels of H2O2 caused a suppressed auxin signal in the early abscission stage and enhanced ETH production during abscission. Furthermore, we found that increasing Pf was required to enhance the turgor pressure to supply the break force for AZ cell separation. Moreover, we observed that SlERF52 bound directly to the SlTIP1;1 promoter to regulate its expression, demonstrating a positive loop in which cytoplasmic H2O2 activates ETH production, which activates SlERF52. This, in turn, induces SlTIP1;1, which leads to elevated cytoplasmic H2O2 and water influx.

Functional characterization of PETIOLULE-LIKE PULVINUS (PLP) gene in abscission zone development in Medicago truncatula and its application to genetic improvement of alfalfa

Alfalfa (Medicago sativa L.) is one of the most important forage crops throughout the world. Maximizing leaf retention during the haymaking process is critical for achieving superior hay quality and maintaining biomass yield. Leaf abscission process affects leaf retention. Previous studies have largely focused on the molecular mechanisms of floral organ, pedicel and seed abscission but scarcely touched on leaf and petiole abscission. This study focuses on leaf and petiole abscission in the model legume Medicago truncatula and its closely related commercial species alfalfa. By analysing the petiolule-like pulvinus (plp) mutant in M. truncatula at phenotypic level (breakstrength and shaking assays), microscopic level (scanning electron microscopy and cross-sectional analyses) and molecular level (expression level and expression pattern analyses), we discovered that the loss of function of PLP leads to an absence of abscission zone (AZ) formation and PLP plays an important role in leaflet and petiole AZ differentiation. Microarray analysis indicated that PLP affects abscission process through modulating genes involved in hormonal homeostasis, cell wall remodelling and degradation. Detailed analyses led us to propose a functional model of PLP in regulating leaflet and petiole abscission. Furthermore, we cloned the PLP gene (MsPLP) from alfalfa and produced RNAi transgenic alfalfa plants to down-regulate the endogenous MsPLP. Down-regulation of MsPLP results in altered pulvinus structure with increased leaflet breakstrength, thus offering a new approach to decrease leaf loss during alfalfa haymaking process.

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.

Genome-wide small RNA profiling reveals tiller development in tall fescue (Festuca arundinacea Schreb)

Background

Tall fescue (Festuca arundinacea Schreb.) is a major cool-season forage and turfgrass species. The low tiller density and size dramatically limits its turf performance and forage yield. MicroRNAs (miRNA)-genes modules play critical roles in tiller development in plants. In this study, a genome-wide small RNA profiling was carried out in two tall fescue genotypes contrasting for tillering production (‘Ch-3’, high tiller production rate and ‘Ch-5’, low tiller production rate) and two types of tissue samples at different tillering development stage (Pre-tillering, grass before tillering; Tillering, grass after tillering). ‘Ch-3’, ‘Ch-5’, Pre-tillering, and Tillering samples were analyzed using high-throughput RNA sequencing.

Results

A total of 222 million high-quality clean reads were generated and 208 miRNAs were discovered, including 148 known miRNAs belonging to 70 families and 60 novel ones. Furthermore, 18 miRNAs were involved in tall fescue tiller development process. Among them, 14 miRNAs displayed increased abundance in both Ch-3 and Tillering plants compared with that in Ch-5 and Pre-tillering plants and were positive with tillering, while another four miRNAs were negative with tiller development. Out of the three miRNAs osa-miR156a, zma-miR528a-3p and osa-miR444b.2, the rest of 15 miRNAs were newfound and associated with tiller development in plants. Based on our previous full-length transcriptome analysis in tall fescue, 28,927 potential target genes were discovered for all identified miRNAs. Most of the 212 target genes of the 18 miRNAs were dominantly enriched into “ubiquitin-mediated proteolysis”, “phagosome”, “fatty acid biosynthesis”, “oxidative phosphorylation”, and “biosynthesis of unsaturated fatty acids” KEGG pathways. In addition, bdi-miR167e-3p targets two kinase proteins EIF2AK4 and IRAK4, and osa-miR397a targets auxin response factor 5, which may be the significant miRNA-genes controllers in tillering development.

Conclusions

This is the first genome-wide miRNA profiles analysis to identify regulators involved in tiller development in cool-season turfgrass. Tillering related 18 miRNAs and their 212 target genes provide novel information for the understanding of the molecular mechanisms of miRNA-genes mediated tiller development in cool-season turfgrass.

Molecular and Hormonal Regulation of Leaf Morphogenesis in Arabidopsis

Shoot apical meristems (SAM) are tissues that function as a site of continuous organogenesis, which indicates that a small pool of pluripotent stem cells replenishes into lateral organs. The coordination of intercellular and intracellular networks is essential for maintaining SAM structure and size and also leads to patterning and formation of lateral organs. Leaves initiate from the flanks of SAM and then develop into a flattened structure with variable sizes and forms. This process is mainly regulated by the transcriptional regulators and mechanical properties that modulate leaf development. Leaf initiation along with proper orientation is necessary for photosynthesis and thus vital for plant survival. Leaf development is controlled by different components such as hormones, transcription factors, miRNAs, small peptides, and epigenetic marks. Moreover, the adaxial/abaxial cell fate, lamina growth, and shape of margins are determined by certain regulatory mechanisms. The over-expression and repression of various factors responsible for leaf initiation, development, and shape have been previously studied in several mutants. However, in this review, we collectively discuss how these factors modulate leaf development in the context of leaf initiation, polarity establishment, leaf flattening and shape.

Research Tools for the Functional Genomics of Plant miRNAs During Zygotic and Somatic Embryogenesis

During early plant embryogenesis, some of the most fundamental decisions on fate and identity are taken making it a fascinating process to study. It is no surprise that higher plant embryogenesis was intensively analysed during the last century, while somatic embryogenesis is probably the most studied regeneration model. Encoded by the MIRNA, short, single-stranded, non-coding miRNAs, are commonly present in all Eukaryotic genomes and are involved in the regulation of the gene expression during the essential developmental processes such as plant morphogenesis, hormone signaling, and developmental phase transition. During the last few years dedicated to miRNAs, analytical methods and tools have been developed, which have afforded new opportunities in functional analyses of plant miRNAs, including (i) databases for in silico analysis; (ii) miRNAs detection and expression approaches; (iii) reporter and sensor lines for a spatio-temporal analysis of the miRNA-target interactions; (iv) in situ hybridisation protocols; (v) artificial miRNAs; (vi) MIM and STTM lines to inhibit miRNA activity, and (vii) the target genes resistant to miRNA. Here, we attempted to summarise the toolbox for functional analysis of miRNAs during plant embryogenesis. In addition to characterising the described tools/methods, examples of the applications have been presented.

Genome-wide analysis of brassinosteroid responsive small RNAs in Arabidopsis thaliana

BACKGROUND

Brassinosteroids (BRs) are a class of phytohormones with important roles in regulating physiological and developmental processes. Small RNAs, including small interfering RNAs and microRNAs (miRNAs), are non-protein coding RNAs that regulate gene expression at the transcriptional and post-transcriptional levels. However, the roles of small RNAs in BR response have not been studied well.

OBJECTIVE

In this study, we aimed to identify BR-responsive small RNA clusters and miRNAs in Arabidopsis. In addition, the effect of BR-responsive small RNAs on their transcripts and target genes were examined.

METHODS

Small RNA libraries were constructed from control and epibrassinolide-treated seedlings expressing wild-type BRI1-Flag protein under its native promoter in the bri1-5 mutant. After sequencing the small RNA libraries, differentially expressed small RNA clusters were identified by examining the expression levels of small RNAs in 100-nt bins of the Arabidopsis genome. To identify the BR-responsive miRNAs, the expression levels of all the annotated mature miRNAs, registered in miRBase, were analyzed. Previously published RNA-seq data were utilized to monitor the BR-responsive expression patterns of differentially expressed small RNA clusters and miRNA target genes.

RESULTS

In results, 38 BR-responsive small RNA clusters, including 30 down-regulated and eight up-regulated clusters, were identified. These differentially expressed small RNA clusters were from miRNA loci, transposons, protein-coding genes, pseudogenes and others. Of these, a transgene, BRI1, accumulates small RNAs, which are not found in the wild type. Small RNAs in this transgene are up-regulated by BRs while BRI1 mRNA is down-regulated by BRs. By analyzing the expression patterns of mature miRNAs, we have identified BR-repressed miR398a-5p and BR-induced miR156g. Although miR398a-5p is down-regulated by BRs, its predicted targets were not responsive to BRs. However, SPL3, a target of BR-inducible miR156g, is down-regulated by BRs.

CONCLUSION

BR-responsive small RNAs and miRNAs identified in this study will provide an insight into the role of small RNAs in BR responses in plants. Especially, we suggest that miR156g/SPL3 module might play a role in BR-mediated growth and development in Arabidopsis.

Transcriptional regulation of MdmiR285N microRNA in apple (Malus x domestica) and the heterologous plant system Arabidopsis thaliana

Malus x domestica microRNA MdmiR285N is a potential key regulator of plant immunity, as it has been predicted to target 35 RNA transcripts coding for different disease resistance proteins involved in plant defense to pathogens. In this study, the promoter region of MdmiR285N was isolated from the apple genome and analyzed in silico to detect potential regulatory regions controlling its transcription. A complex network of putative regulatory elements involved in plant growth and development, and in response to different hormones and stress conditions, was identified. Activity of the β-Glucoronidase (GUS) reporter gene driven by the promoter of MdmiR285N was examined in transgenic apple, demonstrating that MdmiR285N was expressed during the vegetative growth phase. Similarly, in transgenic Arabidopsis thaliana, spatial and temporal patterns of GUS expression revealed that MdmiR285N was differentially regulated during seed germination, vegetative phase change, and reproductive development. To elucidate the role of MdmiR285N in plant immunity, MdmiR285N expression in wild-type apple plants and GUS activity in transgenic apple and Arabidopsis thaliana plants were monitored in response to Erwinia amylovora and Pseudomonas syringae pv. Tomato DC3000. A significant decrease of MdmiR285N levels and GUS expression was observed during host-pathogen infections. Overall, these data suggest that MdmiR285N is involved in the biotic stress response, plant growth, and reproductive development.

Genome-wide identification of microRNAs involved in the regulation of fruit ripening and climacteric stages in melon (Cucumis melo)

Fruit ripening is influenced by multiple plant hormones and the regulation of genes. However, studies on posttranscriptional regulators (e.g., miRNAs) of fruit growth and ripening are limited. We used miRNA sequencing and degradome methods to identify miRNAs and their target genes in melon (Cucumis melo cv. Hetao melon). A total of 61 conserved miRNAs and 36 novel miRNAs were identified from fruit growth, ripening, climacteric, and postclimacteric developmental stage samples, of which 32 conserved miRNAs were differentially expressed between developmental stage samples. Sixty-two target genes of 43 conserved miRNAs and 1 novel miRNA were identified from degradome sequencing. To further investigate miRNA influencing fruit ripening, transgenic melon plants overexpressing pre-cme-miR393 (cme-miR393-OE) were generated and characterized. The results showed that fruit ripening was delayed in cme-miR393-OE transgenic lines compared to nontransgenic fruits. The target of cme-miR393 was also identified, and the expression of CmAFB2 was repressed in transgenic plants. These results provide evidence that miRNA regulates melon fruit ripening and provide potential targets to improve the horticultural traits of melon fruit.

MicroRNA160 regulates leaf curvature in potato (Solanum tuberosum L. cv. Désirée)

Leaf development is a complex process and factors such as size, shape, curvature, compounding, and texture determine the final leaf morphology. MicroRNA160 is one of the crucial players that has been shown to regulate lamina formation and compounding in tomato. In this study, we show that miR160 also regulates leaf curvature in potato. miR160 targets a group of Auxin Response Factors - StARF10, StARF16, and StARF17 - that are proposed to function majorly as repressors of auxin signaling. We observed that overexpression of miR160 (miR160-OE) results in decrease in the levels of these ARFs along with hypersensitivity to exogenous auxin treatment, whereas knockdown of miR160 (miR160-KD) causes increased ARF levels and auxin hyposensitivity. The leaves of miR160-OE plants have a high positive curvature, but of miR160-KD plants are flattened compared to wildtype. A prolonged activation of cell cycle - as indicated by increased levels of StCYCLIND3;2 - in the center region of miR160-OE leaves appears to have caused this positive curvature. However, a comparable StTCP4 activity at both center and margin regions of miR160-KD leaves could be the cause for its flattened leaf phenotype. In summary, we show that miR160 plays an important role in regulating leaf curvature in potato plants.

Dissection of complex traits of tomato in the post-genome era

We present the main advances of dissection of complex traits in tomato by omics, the genes identified to control complex traits and the application of CRISPR/Cas9 in tomato breeding. Complex traits are believed to be under the control of multiple genes, each with different effects and interaction with environmental factors. Advance development of sequencing and molecular technologies has enabled the recognition of the genomic structure of most organisms and the identification of a nearly limitless number of markers that have made it to accelerate the speed of QTL identification and gene cloning. Meanwhile, multiomics have been used to identify the genetic variations among different tomato species, determine the expression profiles of genes in different tissues and at distinct developmental stages, and detect metabolites in different pathways and processes. The combination of these data facilitates to reveal mechanism underlying complex traits. Moreover, mutants generated by mutagens and genome editing provide relatively rich genetic variation for deciphering the complex traits and exploiting them in tomato breeding. In this article, we present the main advances of complex trait dissection in tomato by omics since the release of the tomato genome sequence in 2012. We provide further insight into some tomato complex traits because of the causal genetic variations discovered so far and explore the utilization of CRISPR/Cas9 for the modification of tomato complex traits.

Genome-wide identification and functional analysis of ARF transcription factors in Brassica juncea var. tumida

Auxin signalling is vital for plant growth and development, from embryogenesis to senescence. Recent studies have shown that auxin regulates biological processes by mediating gene expression through a family of functionally original DNA-binding auxin response factors, which exist in a large multi-gene family in plants. However, to date, no information has been available about characteristics of the ARF gene family in Brassica juncea var. tumida. In this study, 65 B. juncea genes that encode ARF proteins were identified in the B. juncea whole-genome, classified into three phylogenetical groups and found to be widely and randomly distributed in the A-and B-genome. Highly conserved proteins were also found within each ortholog based on gene structure and conserved motifs, as well as clustering level. Furthermore, promoter cis-element analysis of BjARFs demonstrated that these genes affect the levels of plant hormones, such as auxin, salicylic, gibberellin acid, MeJA, abscisic acid, and ethylene. Expression analysis showed that differentially expressed BjARF genes were detected during the seedling stage, tumor stem development and the flowering period of B. juncea. Interestingly, we found that BjARF2b_A, BjARF3b_A, BjARF6b_A, and BjARF17a_B were significantly expressed in tumor stem, and an exogenous auxin assay indicated that these genes were sensitive to auxin and IAA signaling. Moreover, eight of the nine BjARF10/16/17 genes and all of the BjARF6/8 genes were involved in post-transcriptional regulation, targeted by Bj-miR160 and Bj-miR167c, respectively. This analysis provides deeper insight of diversification for ARFs and will facilitate further dissection of ARF gene function in B. juncea.

MicroRNA1917-CTR1-LIKE PROTEIN KINASE 4 impacts fruit development via tuning ethylene synthesis and response

MicroRNA1917 (miR1917) is a newly identified miRNAs that regulate ethylene responses in tomato. However, evidence is still limited about its functions in fruit development and ripening. Here, we investigated the possible roles of miR1917-SlCTR4 module in tomato fruit development. We generated miR1917 knock-down mutants by expressing Short Tandem Target Mimic (STTM1917). qRT-PCR and northern-blot analyses suggested that the expression of miR1917 are down-regulated in STTM1917. Concomitantly, miR1917-targeted SlCTR4 gene was up-regulated. STTM1917 plants showed a series of developmental phenotypes, including larger biomass, longer terminal leaflet, bigger floral organ and enhanced fruit and seed size. RNA-seq and qRT-PCR analyses suggested that the expression levels of numerous miRNAs and genes in the transgenic line were significantly altered compared to the wild type. These miRNAs and genes include fruit development-related miRNAs, fruit ripening-related transcription factors and ethylene metabolism genes. Altogether, our results demonstrated that working in concert with ripening regulators, miR1917 might regulate multiple genes in ethylene pathway, thereby modulating fruit development. Our results further indicated that fine-tuning miRNAs expression via STTM can be deployed for agronomic improvement of tomato.

The peu-miR160a-PeARF17.1/PeARF17.2 module participates in the adventitious root development of poplar

Deep roots give rise to flourishing leaves, and the two complement each other. However, the genetic mechanisms underlying adventitious rooting for forest trees have remained elusive. In this study, we verified that peu-miR160a targets six poplar genes AUXIN RESPONSE FACTORS (ARFs), PeARF10.1, PeARF16.1, PeARF16.2, PeARF16.3, PeARF17.1 and PeARF17.2, using 5'RLM-RACE. Interaction experiments with peu-miR160a and PeARFs in poplar protoplasts further confirmed that peu-miR160a targets and negatively regulates the six PeARFs. Peu-miR160a and its target genes exhibited obvious temporal expression in different stages of adventitious root development, and they could also be induced by IAA and abscisic acid. Peu-miR160a-overexpressing lines exhibited a significant shortening of adventitious root length, an increase in the number of lateral roots, severe dwarfing and shortened internodes. In addition, the overexpression of PeARF17.1 or mPeARF17.2 (peu-miR160a-resistant version of PeARF17.2) significantly increased the number of adventitious roots. Furthermore, PeARF17.1-overexpressing lines had multiple branches with no visible trunk, although the adventitious root length of the PeARF17.1-overexpressing lines was significantly increased. Our findings reveal that the peu-miR160a - PeARF17.1/PeARF17.2 module is an important regulator involved in the development of the adventitious roots of poplar.

Integrated Analysis of Small RNA, Transcriptome and Degradome Sequencing Provides New Insights into Floral Development and Abscission in Yellow Lupine (Lupinus luteus L.)

The floral development in an important legume crop yellow lupine (Lupinus luteus L., Taper cv.) is often affected by the abscission of flowers leading to significant economic losses. Small non-coding RNAs (sncRNAs), which have a proven effect on almost all developmental processes in other plants, might be of key players in a complex net of molecular interactions regulating flower development and abscission. This study represents the first comprehensive sncRNA identification and analysis of small RNA, transcriptome and degradome sequencing data in lupine flowers to elucidate their role in the regulation of lupine generative development. As shedding in lupine primarily concerns flowers formed at the upper part of the inflorescence, we analyzed samples from extreme parts of raceme separately and conducted an additional analysis of pedicels from abscising and non-abscising flowers where abscission zone forms. A total of 394 known and 28 novel miRNAs and 316 phased siRNAs were identified. In flowers at different stages of development 59 miRNAs displayed differential expression (DE) and 46 DE miRNAs were found while comparing the upper and lower flowers. Identified tasiR-ARFs were DE in developing flowers and were strongly expressed in flower pedicels. The DEmiR-targeted genes were preferentially enriched in the functional categories related to carbohydrate metabolism and plant hormone transduction pathways. This study not only contributes to the current understanding of how lupine flowers develop or undergo abscission but also holds potential for research aimed at crop improvement.

Identification of miRNAs and Their Target Genes Involved in Cucumber Fruit Expansion Using Small RNA and Degradome Sequencing

Fruit expansion is an essential and very complex biological process. Regulatory roles of microRNAs (miRNAs) and miRNA-mRNA modules in the cucumber fruit expansion are not yet to be investigated. In this work, 1253 known and 1269 novel miRNAs were identified from nine cucumber fruit small RNA (sRNA) libraries through high-throughput sequencing. A total of 105 highly differentially expressed miRNAs were recognized in the fruit on five days post anthesis with pollination (EXP_5d) sRNA library. Further, expression patterns of 11 differentially expressed miRNAs were validated by quantitative real-time PCR (qRT-PCR). The expression patterns were similar to sRNAs sequencing data. Transcripts of 1155 sequences were predicted as target genes of differentially expressed miRNAs by degradome sequencing. Gene Ontology (GO) enrichment showed that these target genes were involved in 24 biological processes, 15 cell components and nine molecular functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that these target genes were significantly enriched in 19 pathways and the enriched KEGG pathways were associated with environmental adaptation, signal transduction and translation. Based on the functional prediction of miRNAs and target genes, our findings suggest that miRNAs have a potential regulatory role in cucumber fruit expansion by targeting their target genes, which provide important data for understanding the miRNA-mediated regulatory networks controlling fruit expansion in cucumber. Specific miRNAs could be selected for further functional research and molecular breeding in cucumber.

A Comparison of sun, ovate, fs8.1 and Auxin Application on Tomato Fruit Shape and Gene Expression

Elongated tomato fruit shape is the result of the action of the fruit shape genes possibly in coordination with the phytohormone auxin. To investigate the possible link between auxin and the fruit shape genes, a series of auxin (2,4-D) treatments were performed on the wild-type and the fruit shape near-isogenic lines (NILs) in Solanum pimpinellifolium accession LA1589 background. Morphological and histological analyses indicated that auxin application approximately 3 weeks before anthesis led to elongated pear-shaped ovaries and fruits, which was mainly attributed to the increase of ovary/fruit proximal end caused by the increase of both cell number and cell size. Fruit shape changes caused by SUN, OVATE and fs8.1 were primarily due to the alterations of cell number along different growth axes. Particularly, SUN caused elongation by extending cell number along the entire proximal-distal axis, whereas OVATE caused fruit elongation in the proximal area, which was most similar to the effect of auxin on ovary shape. Expression analysis of flower buds at different stages in fruit shape NILs indicated that SUN had a stronger impact on the transcriptome than OVATE and fs8.1. The sun NIL differentially expressed genes were enriched in several biological processes, such as lipid metabolism, ion transmembrane and actin cytoskeleton organization. Additionally, SUN also shifted the expression of the auxin-related genes, including those involved in auxin biosynthesis, homeostasis, signal transduction and polar transport, indicating that SUN may regulate ovary/fruit shape through modifying the expression of auxin-related genes very early during the formation of the ovary in the developing flower.