Project description:Background: The change from juvenile to mature phase in woody plants is often accompanied by a gradual loss of rooting ability, as well as by reduced microRNA (miR) 156 and increased miR172 expression. Results: We characterized the population of miRNAs of Eucalyptus grandis and compared by Northern blot the gradual reduction in miR156 and increase in miR172 expression during development to the loss of rooting ability. Forty known and eight novel miRNAs were discovered and their predicted targets are listed. The expression pattern of nine miRNAs was determined during adventitious root formation in juvenile and mature cuttings. While the expression levels of miR156 and miR172 were inverse in juvenile and mature tissues, no mutual relationship was found between high miR156 expression and rooting ability, or high miR172 expression and loss of rooting ability. This is shown both in E. grandis and also in E. brachyphylla, in which explants that underwent rejuvenation in tissue culture conditions were also examined. Conclusions: It is suggested that in these Eucalyptus species, there is no correlation between the switch of miR156 with miR172 expression in the stems and the loss of rooting ability.
Project description:In plants, juvenile to adult phase transition is regulated by the sequential activity of two microRNAs: miR156 and miR172. A decline in miR156 and increase in miR172 abundance is associated with phase transition. There is very limited information on phase transition in economically important horticultural tree crops, which have a significantly long vegetative phase affecting fruit bearing. Here we profiled various molecular cues known to be involved in phase transition and flowering, including the microRNAs miR156 and miR172, in three horticultural tree crops avocado (Persea americana), mango (Mangifera indica) and macadamia (Macadamia integrifolia). We observed that miR156 expression decreases as these trees age and can potentially be used as a juvenility marker. Consistent with findings in annual plants, we also observed conserved regulation of the miR156-SPL3/4/5 regulatory module in these genetically distant tree crops, suggesting that this pathway may play a highly conserved role in vegetative identity. Meanwhile, the abundance of miR172 and its target AP2-like genes, as well as the accumulation level of SPL9 transcripts, were not related with plant age in these crops except in avocado where miR172 expression increased steadily. Finally, we demonstrate that various floral genes, including AP1 and SOC1 were upregulated in the reproductive phase and can be used as potential markers for the reproductive phase transition. Overall, this study provides an insight into the molecular associations of juvenility and phase transition in horticultural trees where crop breeding and improvement is encumbered by long juvenile phases.
Project description:The APETALA2 (AP2) transcription factor regulates flower development, floral transition and shoot apical meristem (SAM) maintenance in Arabidopsis. AP2 is also regulated at the post-transcriptional level by microRNA172 (miR172), but the contribution of this to SAM maintenance is poorly understood. We generated transgenic plants carrying a form of AP2 that is resistant to miR172 (rAP2) or carrying a wild-type AP2 susceptible to miR172. Phenotypic and genetic analyses were performed on these lines and mir172 mutants to study the role of AP2 regulation by miR172 on meristem size and the rate of flower production. We found that rAP2 enlarges the inflorescence meristem by increasing cell size and cell number. Misexpression of rAP2 from heterologous promoters showed that AP2 acts in the central zone (CZ) and organizing center (OC) to increase SAM size. Furthermore, we found that AP2 is negatively regulated by AUXIN RESPONSE FACTOR 3 (ARF3). However, genetic analyses indicated that ARF3 also influences SAM size and flower production rate independently of AP2. The study identifies miR172/AP2 as a regulatory module controlling inflorescence meristem size and suggests that transcriptional regulation of AP2 by ARF3 fine tunes SAM size determination.
Project description:MicroRNA172 (miR172) plays a role in regulating a diverse range of plant developmental processes. However, its role in regulating anthocyanin biosynthesis is unclear. In this study, we show that transgenic apple plants over-expressing miR172 show a reduction in red colouration and anthocyanin accumulation in multiple tissue types. This reduction was consistent with decreased expression of APETALA2 homolog MdAP2_1a (a miR172 target gene), MdMYB10, and targets of MdMYB10, as demonstrated by both RNA-seq and RT-PCR analyses. During the onset of anthocyanin biosynthesis in apple fruit skin, miR172 transcript abundance was negatively correlated and MdAP2_1a mRNA concentration was positively correlated with fruit skin red-colouration. The positive role of MdAP2_1a in regulating anthocyanin biosynthesis was supported by the enhanced petal anthocyanin accumulation in transgenic tobacco plants overexpressing MdAP2_1a, and by the reduction in anthocyanin accumulation in apple and cherry fruits transfected with an MdAP2_1a virus-induced-gene-silencing construct. We demonstrated that MdAP2_1a could bind directly to the promoter and protein sequences of MdMYB10 in yeast and tobacco, and enhance MdMYB10 promotor activity. In Arabidopsis, over-expression of miR172 reduced anthocyanin concentration and RNA transcript abundance of anthocyanin genes in plantlets cultured on medium containing 7% sucrose. The anthocyanin content and RNA abundance of anthocyanin genes could be partially restored by using a synonymous mutant of MdAP2_1a, which had lost the miR172 target sequences at mRNA level, but not restored by using a WT MdAP2_1a. These results indicate that miR172 inhibits anthocyanin biosynthesis through suppressing the expression of an AP2 transcription factor that positively regulates MdMYB10.
Project description:Legumes interact with rhizobial bacteria to form nitrogen-fixing root nodules. Host signalling following mutual recognition ensures a specific response, but is only partially understood. Focusing on the stage of epidermal infection with Mesorhizobium loti, we analysed endogenous small RNAs (sRNAs) of the model legume Lotus japonicus to investigate their involvement in host response regulation. We used Illumina sequencing to annotate the L. japonicus sRNA-ome and isolate infection-responsive sRNAs, followed by candidate-based functional characterization. Sequences from four libraries revealed 219 novel L. japonicus micro RNAs (miRNAs) from 114 newly assigned families, and 76 infection-responsive sRNAs. Unlike infection-associated coding genes such as NODULE INCEPTION (NIN), a micro RNA 172 (miR172) isoform showed strong accumulation in dependency of both Nodulation (Nod) factor and compatible rhizobia. The genetics of miR172 induction support the existence of distinct epidermal and cortical signalling events. MIR172a promoter activity followed a previously unseen pattern preceding infection thread progression in epidermal and cortical cells. Nodule-associated miR172a expression was infection-independent, representing the second of two genetically separable activity waves. The combined data provide a valuable resource for further study, and identify miR172 as an sRNA marking successful epidermal infection. We show that miR172 acts upstream of several APETALA2-type (AP2) transcription factors, and suggest that it has a role in fine-tuning AP2 levels during bacterial symbiosis.
Project description:Background: The change from juvenile to mature phase in woody plants is often accompanied by a gradual loss of rooting ability, as well as by reduced microRNA (miR) 156 and increased miR172 expression. Results: We characterized the population of miRNAs of Eucalyptus grandis and compared by Northern blot the gradual reduction in miR156 and increase in miR172 expression during development to the loss of rooting ability. Forty known and eight novel miRNAs were discovered and their predicted targets are listed. The expression pattern of nine miRNAs was determined during adventitious root formation in juvenile and mature cuttings. While the expression levels of miR156 and miR172 were inverse in juvenile and mature tissues, no mutual relationship was found between high miR156 expression and rooting ability, or high miR172 expression and loss of rooting ability. This is shown both in E. grandis and also in E. brachyphylla, in which explants that underwent rejuvenation in tissue culture conditions were also examined. Conclusions: It is suggested that in these Eucalyptus species, there is no correlation between the switch of miR156 with miR172 expression in the stems and the loss of rooting ability. Examination of microRNA in seedlings of Eucalyptus grandis
Project description:Legumes and rhizobia establish a nitrogen-fixing symbiosis that involves the formation of a lateral root organ, the nodule, and the infection process that allows intracellular accommodation of rhizobia within nodule cells. This process involves significant gene expression changes regulated at the transcriptional and post-transcriptional levels. We have previously shown that a transcript encoding the subunit 3 of the Superkiller Complex (SKI), which guides mRNAs to the exosome for 3´-to-5´ degradation, is required for nodule formation and bacterial persistence within the nodule, as well as the induction of early nodulation genes (e.g., MtENOD40) during the Medicago truncatula-Sinorhizobium meliloti symbiosis. Here, we reveal through transcript degradome and small RNA sequencing analysis that knockdown of MtSKI3 impairs the miR172-directed endonucleolytic cleavage of the mRNA encoding Nodule Number Control 1 (MtNNC1), an APETALA2 transcription factor that negatively modulates nodulation. Knockdown of MtNNC1 enhances nodule number, bacterial infection, and the induction of MtENOD40 upon inoculation with S. meliloti whereas overexpression of a miR172-resistant form of MtNNC1 significantly reduces nodule formation. This work identifies miR172 cleavage of MtNNC1 and its control by MtSKI3, a component of the 3´-to- 5´mRNA degradation pathway, as a new regulatory hub controlling indeterminate nodulation.
Project description:The emerging picture of transcriptional regulation is one of unexpected complexity. It is now clear that single transcription factors control hundreds, if not thousands, of direct targets by binding their genomic loci, but it is not understood how many of these are major players and how many are supporting cast. To address this, we leverage a well-characterized developmental network in Arabidopsis and map genome-wide binding of related proteins in multiple tissues. The transcription factor APETALA2 (AP2) has numerous functions, including roles in floral organ identity, seed development and stem cell maintenance. We focus on the role of AP2 in the floral transition and map direct targets on a genome-wide scale. We show that ap2 mutants flower early in long and short days, and that AP2 binds to many loci, most prominently floral pathway integrators, microRNAs and floral organ identity genes, many of which exhibit AP2-dependent transcription. Opposing, logical effects are evident in AP2 binding to two developmental microRNA genes that control AP2 expression, with AP2 positively regulating miR156 and negatively regulating miR172, forming a complex direct feedback loop, which also included all but one of the AP2-like miR172 target clade members. We also seek conserved targets by comparing the genome-wide direct target repertoire of AP2 with that of SCHLAFMÜTZE (SMZ), another member of the AP2-like miR172 target clade that shares partial redundancy, as evidenced by a hexuple mutant for the entire clade that flowered extremely early. Clear similarities and divergence are exposed in the AP2 and SMZ direct target repertoires. Finally, using an inducible expression system, we demonstrate that AP2 has dual molecular roles. It functions both as a transcriptional activator and repressor, directly inducing the expression of the floral repressor AGAMOUS-LIKE 15 (AGL15), and directly repressing the transcription of floral activators like SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). ChIP-Seq of two biological replicates for ATH-AP2 and respective control samples
Project description:The emerging picture of transcriptional regulation is one of unexpected complexity. It is now clear that single transcription factors control hundreds, if not thousands, of direct targets by binding their genomic loci, but it is not understood how many of these are major players and how many are supporting cast. To address this, we leverage a well-characterized developmental network in Arabidopsis and map genome-wide binding of related proteins in multiple tissues. The transcription factor APETALA2 (AP2) has numerous functions, including roles in floral organ identity, seed development and stem cell maintenance. We focus on the role of AP2 in the floral transition and map direct targets on a genome-wide scale. We show that ap2 mutants flower early in long and short days, and that AP2 binds to many loci, most prominently floral pathway integrators, microRNAs and floral organ identity genes, many of which exhibit AP2-dependent transcription. Opposing, logical effects are evident in AP2 binding to two developmental microRNA genes that control AP2 expression, with AP2 positively regulating miR156 and negatively regulating miR172, forming a complex direct feedback loop, which also included all but one of the AP2-like miR172 target clade members. We also seek conserved targets by comparing the genome-wide direct target repertoire of AP2 with that of SCHLAFMÜTZE (SMZ), another member of the AP2-like miR172 target clade that shares partial redundancy, as evidenced by a hexuple mutant for the entire clade that flowered extremely early. Clear similarities and divergence are exposed in the AP2 and SMZ direct target repertoires. Finally, using an inducible expression system, we demonstrate that AP2 has dual molecular roles. It functions both as a transcriptional activator and repressor, directly inducing the expression of the floral repressor AGAMOUS-LIKE 15 (AGL15), and directly repressing the transcription of floral activators like SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1).
Project description:Trough a two components inducible system, we expressed ectopically in the SAM a resistant version of AP2 to the regulation of miR172 (AP2m3). The differentially expressed genes by AP2 induction allows the identification of differents groups of genes that could mediate AP2 functions in the SAM.