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Potato miR160 is crucial for both local and SAR responses to the late blight pathogen Phytophthora infestans and modulates antagonistic cross-talk between auxin-mediated growth and salicylic acid-mediated defense responses. Abstract To combat pathogen infection, plants employ local defenses in infected sites and elicit systemic acquired resistance (SAR) in distant tissues. MicroRNAs have been shown to play a significant role in local defense, but their association with SAR is unknown. In addition, no such studies of the interaction between potato and Phytophthora infestans have been reported. We investigated the role of miR160 in local and SAR responses to P. infestans infection in potato. Expression analysis revealed induced levels of miR160 in both local and systemic leaves of infected wild-type plants. miR160 overexpression and knockdown plants exhibited increased susceptibility to infection, suggesting that miR160 levels equivalent to those of wild-type plants may be necessary for mounting local defense responses. Additionally, miR160 knockdown lines failed to elicit SAR, and grafting assays indicated that miR160 is required in both local and systemic leaves to trigger SAR. Consistently, SAR-associated signals and genes were dysregulated in miR160 knockdown lines. Furthermore, analysis of the expression of defense and auxin pathway genes and direct regulation of StGH3.6, a mediator of salicylic acid-auxin cross-talk, by the miR160 target StARF10 revealed the involvement of miR160 in antagonistic cross-talk between salicylic acid-mediated defense and auxin-mediated growth pathways. Overall, our study demonstrates that miR160 plays a crucial role in local defense and SAR responses during the interaction between potato and P. infestans.

Global warming is causing a negative impact on plant growth and adversely impacts on crop yield. MicroRNAs (miRNAs) are critical in regulating the expression of genes involved in plant development as well as defense responses. The effects of miRNAs on heat-stressed warrants further investigation. Heat stress increased the expression of miR160 and its precursors but considerably reduced that of its targets, , and . To study the roles of miR160 during heat stress, transgenic plants overexpressing a (160OE) and artificial miR160 (MIM160), which mimics an inhibitor of miR160, were created. T-DNA insertion mutants of miR160 targets were also used to examine their tolerances to heat stress. Results presented that overexpressing miR160 improved seed germination and seedling survival under heat stress. The lengths of hypocotyl elongation and rachis were also longer in 160OE than the wild-type (WT) plants under heat stress. Interestingly, MIM160 plants showed worse adaption to heat. In addition, , and mutants presented similar phenotypes to 160OE under heat stress to advance abilities of thermotolerance. Moreover, transcriptome and qRT-PCR analyses revealed that , and expression levels were regulated by heat in 160OE, MIM160, , and plants. Hence, miR160 altered the expression of the heat shock proteins and plant development to allow plants to survive heat stress.

A plethora of developmental and physiological processes in land plants is influenced by auxin, to a large extent via alterations in gene expression by AUXIN RESPONSE FACTORs (ARFs). The canonical auxin transcriptional response system is a land plant innovation, however, charophycean algae possess orthologues of at least some classes of ARF and AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) genes, suggesting that elements of the canonical land plant system existed in an ancestral alga. We reconstructed the phylogenetic relationships between streptophyte ARF and AUX/IAA genes and functionally characterized the solitary class C ARF, MpARF3, in Marchantia polymorpha. Phylogenetic analyses indicate that multiple ARF classes, including class C ARFs, existed in an ancestral alga. Loss- and gain-of-function MpARF3 alleles result in pleiotropic effects in the gametophyte, with MpARF3 inhibiting differentiation and developmental transitions in multiple stages of the life cycle. Although loss-of-function Mparf3 and Mpmir160 alleles respond to exogenous auxin treatments, strong miR-resistant MpARF3 alleles are auxinin-sensitive, suggesting that class C ARFs act in a context-dependent fashion. We conclude that two modules independently evolved to regulate a pre-existing ARF transcriptional network. Whereas the auxin-TIR1-AUX/IAA pathway evolved to repress class A/B ARF activity, miR160 evolved to repress class C ARFs in a dynamic fashion.

Summary MicroRNAs (miRNAs) play crucial roles in plant development and secondary metabolism through different modes of sequence‐specific interaction with their targets. Artemisinin biosynthesis is extensively regulated by phytohormones. However, the function of phytohormone‐responsive miRNAs in artemisinin biosynthesis remains enigmatic. Thus, we combined the analysis of transcriptomics, small RNAs, and the degradome to generate a comprehensive resource for identifying key miRNA‐target circuits involved in the phytohormone‐induced process of artemisinin biosynthesis in Artemisia annua. In total, 151 conserved and 52 novel miRNAs and their 4132 targets were determined. Based on the differential expression analysis, miR160 was selected as a potential miRNA involved in artemisinin synthesis. Overexpressing MIR160 significantly impaired glandular trichome formation and suppressed artemisinin biosynthesis in A. annua, while repressing its expression resulted in the opposite effect, indicating that miR160 negatively regulates glandular trichome development and artemisinin biosynthesis. RNA ligase‐mediated 5′ RACE and transient transformation assays showed that miR160 mediates the RNA cleavage of Auxin Response Factor 1 (ARF1) in A. annua. Furthermore, ARF1 was shown to increase artemisinin synthesis by activating AaDBR2 expression. Taken together, our results reveal the intrinsic link between the miR160‐ARF1 module and artemisinin biosynthesis, and may expedite the innovation of metabolic engineering approaches for high and stable production of artemisinin in the future. miR160 responses to SA, JA induction and forms a module with target gene ARF1 to regulate glandular trichome development and artemisnin biosynthesis in Artemisia annua.

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.

In Arabidopsis thaliana (Arabidopsis), microRNA160 (miR160) regulates the expression of AUXIN RESPONSE FACTOR10 (ARF10), ARF16 and ARF17 throughout development, including the development of the root system. We have previously shown that in addition to DOUBLE-STRANDED RNA BINDING1 (DRB1), DRB2 is also involved in controlling the rate of production of specific miRNA cohorts in the tissues where DRB2 is expressed in wild-type Arabidopsis plants. In this study, a miR160 overexpression transgene (MIR160B) and miR160-resistant transgene versions of ARF10 and ARF16 (mARF10 and mARF16) were introduced into wild-type Arabidopsis plants and the drb1 and drb2 single mutants to determine the degree of requirement of DRB2 to regulate the miR160 expression module as part of root development. Via this molecular modification approach, we show that in addition to DRB1, DRB2 is required to regulate the level of miR160 production from its precursor transcripts in Arabidopsis roots. Furthermore, we go on to correlate the altered abundance of miR160 or its ARF10, ARF16 and ARF17 target genes in the generated series of transformant lines with the enhanced development of the root system displayed by these plant lines. More specifically, promotion of primary root elongation likely stemmed from enhancement of miR160-directed ARF17 expression repression, while the promotion of lateral and adventitious root formation was the result of an elevated degree of miR160-directed regulation of ARF17 expression, and to a lesser degree, ARF10 and ARF16 expression. Taken together, the results presented in this study identify the requirement of the functional interplay between DRB1 and DRB2 to tightly control the rate of miR160 production, to in turn ensure the appropriate degree of miR160-directed ARF10, ARF16 and ARF17 gene expression regulation as part of normal root system development in Arabidopsis.

DOUBLE-STRANDED RNA BINDING (DRB) proteins DRB1, DRB2, and DRB4 are essential for microRNA (miRNA) production in Arabidopsis thaliana (Arabidopsis) with miR160, and its target genes, AUXIN RESPONSE FACTOR10 (ARF10), ARF16, and ARF17, forming an auxin responsive miRNA expression module crucial for root development. Methods: Wild-type Arabidopsis plants (Columbia-0 (Col-0)) and the drb1, drb2, and drb12 mutants were treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), and the miR160-mediated response of these four Arabidopsis lines was phenotypically and molecularly characterized. Results: In 2,4-D-treated Col-0, drb1 and drb2 plants, altered miR160 abundance and ARF10, ARF16, and ARF17 gene expression were associated with altered root system development. However, miR160-directed molecular responses to treatment with 2,4-D was largely defective in the drb12 double mutant. In addition, via profiling of molecular components of the miR160 expression module in the roots of the drb4, drb14, and drb24 mutants, we uncovered a previously unknown role for DRB4 in regulating miR160 production. Conclusions: The miR160 expression module forms a central component of the molecular and phenotypic response of Arabidopsis plants to exogenous auxin treatment. Furthermore, DRB1, DRB2, and DRB4 are all required in Arabidopsis roots to control miR160 production, and subsequently, to appropriately regulate ARF10, ARF16, and ARF17 target gene expression.

We performed differential gene expression (DGE) and co-expression analyses with genes encoding components of hormonal signaling pathways and the ∼400 annotated transcription factors (TFs) of across multiple developmental stages of the life cycle. We identify a putative auxin-related co-expression module that has significant overlap with transcripts induced in auxin-treated tissues. Consistent with phylogenetic and functional studies, the class C ARF, Mp , is not part of the auxin-related co-expression module and instead is associated with transcripts enriched in gamete-producing gametangiophores. We analyze the Mp and Mp mutant transcriptomes in the context of coexpression to suggest that Mp may antagonize the reproductive transition via activating the Mp and Mp precursors whose encoded microRNAs target (SPL) transcripts of Mp and Mp . Both Mp genes are part of the Mp co-expression group corroborating their functional significance. We provide evidence of the independence of Mp from the auxin-signaling module and provide new testable hypotheses on the role of auxin-related genes in patterning meristems and differentiation events in liverworts.

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.

Cotton fiber is the most important raw material for the textile industry. MicroRNAs are involved in regulating cotton-fiber development, but a role in fiber elongation has not been demonstrated. In this study, miR160a was found to be differentially expressed in elongating fibers between two interspecific (between Gossypium hirsutum and G. barbadense) backcross inbred lines (BILs) with different fiber lengths. The gene MIR160 colocalized with a previously mapped fiberlength quantitative trait locus. Its target gene ARF17 was differentially expressed between the two BILs during fiber elongation, but in the inverse fashion. Bioinformatics was used to analyze the MIR160 family in both G. hirsutum and G. barbadense. Moreover, qRT–PCR analysis identified MIR160a as the functional MIR160 gene encoding the miR160a precursor during fiber elongation. Using virus-induced gene silencing and overexpression, overexpressed MIR160a_A05 resulted in significantly longer fibers compared with wild type, whereas suppression of miR160 resulted in significantly shorter fibers. Expression levels of the target gene auxin-response factor 17 (ARF17) and related genes GH3 in the two BILs and/or the virus-infected plants demonstrated similar changes in response to modulation of miR160a level. Finally, overexpression or suppression of miR160 increased or decreased, respectively, the cellular level of indole-3-acetic acid, which is involved in fiber elongation. These results describe a specific regulatory mechanism for fiber elongation in cotton that can be utilized for future crop improvement.