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Systemic mRNA transport depends on m 5 C methylation, nuclear mRNA export factors and developmental phase changes
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Abstract
In Arabidopis a high number of distinct mRNAs move from shoot to root. We previously reported on the correlation of m ⁵ C-methylation and lack of mRNA transport in juvenile plants depending on the RNA methyltransferases DNMT2 NSUN2B . However, to our surprise we uncovered that lack of DNMT2 NSUN2B (writer) activity did not abolished transport of TCTP1 and HSC70.1 transcripts in flowering plants. We uncovered that transport of both transcripts is reinstated in dnmt2 nsun2b mutants after commitment to flowering. This finding suggests that additional factors are seemingly involved in regulating / mediating mRNA transport. In search of such candidates, we identified the two ALY2 and ALY4 nuclear mRNA export factors belonging to the ALYREF family as bona fide m ⁵ C readers mediating mRNA transport. We show that both proteins are allocated along the phloem and that they bind preferentially to mobile mRNAs. MST measurements indicate that ALY2 and ALY4 bind to mobile mRNAs with relative high affinity with ALY4 showing higher affinity towards m ⁵ C-methylated mobile mRNAs. An analysis of the graft-mobile transcriptome of juvenile heterografted-grafted wild type, dnmt2 nsun2b , aly2 and aly4 mutants revealed that the nuclear export factors are key regulators of mRNA transport. We suggest that depending on the developmental stage m ⁵ C methylation has a negative and positive regulatory function in mRNA transport and acts together with ALY2 and ALY4 to facilitate mRNA transport in both juvenile and flowering plants.
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The HSC70/HSP70 family of heat shock proteins are evolutionarily conserved chaperones involved in protein folding, protein transport, and RNA binding. Arabidopsis HSC70 chaperones are thought to act as housekeeping chaperones and as such are involved in many growth‐related pathways. Whether Arabidopsis HSC70 binds RNA and whether this interaction is functional has remained an open question.
We provide evidence that the HSC70.1 chaperone binds its own mRNA via its C‐terminal short variable region (SVR) and inhibits its own translation.
The SVR encoding mRNA region is necessary for HSC70.1 transcript mobility to distant tissues and that HSC70.1 transcript and not protein mobility is required to rescue root growth and flowering time of hsc70 mutants. We propose that this negative protein‐transcript feedback loop may establish an on‐demand chaperone pool that allows for a rapid response to stress.
In summary, our data suggest that the Arabidopsis HSC70.1 chaperone can form a complex with its own transcript to regulate its translation and that both protein and transcript can act in a noncell‐autonomous manner, potentially maintaining chaperone homeostasis between tissues.
The long-distance transport of messenger RNAs (mRNAs) has been shown to be important for several developmental processes in plants. A popular method for identifying travelling mRNAs is to perform RNA-Seq on grafted plants. This approach depends on the ability to correctly assign sequenced mRNAs to the genetic background from which they originated. The assignment is often based on the identification of single-nucleotide polymorphisms (SNPs) between otherwise identical sequences. A major challenge is therefore to distinguish SNPs from sequencing errors. Here, we show how Bayes factors can be computed analytically using RNA-Seq data over all the SNPs in an mRNA. We used simulations to evaluate the performance of the proposed framework and demonstrate how Bayes factors accurately identify graft-mobile transcripts. The comparison with other detection methods using simulated data shows how not taking the variability in read depth, error rates and multiple SNPs per transcript into account can lead to incorrect classification. Our results suggest experimental design criteria for successful graft-mobile mRNA detection and show the pitfalls of filtering for sequencing errors or focusing on single SNPs within an mRNA.
Background
Epigenetic mark such as DNA methylation plays pivotal roles in regulating ripening of both climacteric and non-climacteric fruits. However, it remains unclear whether mRNA m⁶A methylation, which has been shown to regulate ripening of the tomato, a typical climacteric fruit, is functionally conserved for ripening control among different types of fruits.
Results
Here we show that m⁶A methylation displays a dramatic change at ripening onset of strawberry, a classical non-climacteric fruit. The m⁶A modification in coding sequence (CDS) regions appears to be ripening-specific and tends to stabilize the mRNAs, whereas m⁶A around the stop codons and within the 3′ untranslated regions is generally negatively correlated with the abundance of associated mRNAs. We identified thousands of transcripts with m⁶A hypermethylation in the CDS regions, including those of NCED5, ABAR, and AREB1 in the abscisic acid (ABA) biosynthesis and signaling pathway. We demonstrate that the methyltransferases MTA and MTB are indispensable for normal ripening of strawberry fruit, and MTA-mediated m⁶A modification promotes mRNA stability of NCED5 and AREB1, while facilitating translation of ABAR.
Conclusion
Our findings uncover that m⁶A methylation regulates ripening of the non-climacteric strawberry fruit by targeting the ABA pathway, which is distinct from that in the climacteric tomato fruit.
The biological functions of epitranscriptomic modification N⁶-methyladenosine (m⁶A) in plants have not been fully understood. CPSF30-L is a predominant isoform of polyadenylation factor CPSF30 and consists of CPSF30-S and m⁶A-binding YTH domain. Little is known about the biological roles of CPSF30-L and the molecular mechanism underlying its m⁶A binding function in alternative polyadenylation (APA). Here we characterized CPSF30-L as an Arabidopsis m⁶A reader whose m⁶A binding function is required for floral transition and abscisic acid (ABA) response. We found the m⁶A binding activity enhances the formation of liquid-like CPSF30-L nuclear bodies, where CPSF30-L mainly recognizes m⁶A-modified far upstream element (FUE) to control polyadenylation site choice. Disruption of CPSF30-L lengthens 3' untranslated region (3' UTR) of three CPSF30-L binding transcripts related with phenotypes, thereby accelerating their mRNA degradation and leading to late flowering and ABA hypersensitivity. This study uncovers a new molecular mechanism for m⁶A-driven phase separation and polyadenylation in plants.
As an important posttranscriptional modification of RNA, 5-methylcytosine (m5C) has attracted increasing interest recently, with accumulating evidence suggesting the involvement of RNA m5C modification in multiple cellular processes as well as tumorigenesis. Cooperatively, advances in m5C detection techniques have enabled transcriptome mapping of RNA methylation at single-nucleotide resolution, thus stimulating m5C-based investigations. In this review, we summarize currently available approaches for detecting m5C distribution in RNA as well as the advantages and disadvantages of these techniques. Moreover, we elucidate the regulatory mechanisms of RNA m5C modification by introducing the molecular structure, catalytic substrates, cellular distributions and biological functions of RNA m5C regulators. The functional consequences of m5C modification on mRNAs, tRNAs, rRNAs and other RNA species, including viral RNAs and vault RNAs, are also discussed. Finally, we review the role of RNA m5C modification in cancer pathogenesis and progression, in hopes of providing new insights into cancer treatment.
N⁶-Methyladenosine (m⁶A) RNA methylation plays important roles during development in different species. However, knowledge of m⁶A RNA methylation in monocots remains limited. In this study, we reported that OsFIP and OsMTA2 are the components of m⁶A RNA methyltransferase complex in rice and uncovered a previously unknown function of m⁶A RNA methylation in regulation of plant sporogenesis. Importantly, OsFIP is essential for rice male gametogenesis. Knocking out of OsFIP results in early degeneration of microspores at the vacuolated pollen stage and simultaneously causes abnormal meiosis in prophase I. We further analyzed the profile of rice m⁶A modification during sporogenesis in both WT and OsFIP loss-of-function plants, and identified a rice panicle specific m⁶A modification motif “UGWAMH”. Interestingly, we found that OsFIP directly mediates the m⁶A methylation of a set of threonine protease and NTPase mRNAs and is essential for their expression and/or splicing, which in turn regulates the progress of sporogenesis. Our findings revealed for the first time that OsFIP plays an indispensable role in plant early sporogenesis. This study also provides evidence for the different functions of the m⁶A RNA methyltransferase complex between rice and Arabidopsis.
Recent heterograft analyses showed that large-scale mRNA movement takes place in the phloem, but the number of mobile transcripts reported varies widely. However, our knowledge of the mechanisms underlying large-scale mRNA movement remains limited. In this study, using a Nicotiana benthamiana/tomato (Solanum lycopersicum) heterograft system and a transgenic approach involving potato (Solanum tuberosum), we found that: 1) the overall mRNA abundance in the leaf is not a good indicator of transcript mobility to the root; 2) increasing the expression levels of non-mobile mRNAs in the companion cells does not promote their mobility; 3) mobile mRNAs undergo degradation during their movement; and 4) some mRNAs arriving in roots move back to shoots. These results indicate that mRNA movement has both regulated and unregulated components. The cellular origins of mobile mRNAs may differ between herbaceous and woody species. Taken together, these findings suggest that the long-distance movement of mRNAs is a complex process and elucidating the physiological roles associated with this movement is challenging but remains an important task for future research.
Methylations at position N6 of internal adenosines (m6As) are the most abundant and widespread mRNA modifications. These modifications play crucial roles in reproduction, growth and development by controlling gene express patterns at the post-transcriptional level. Their function is decoded by readers that share the YTH domain, which forms a hydrophobic pocket that directly accommodates the m6A residues. While the physiological and molecular functions of YTH readers have been extensively studied in animals, little is known about plant readers, even though m6As are crucial for plant survival and development. Viridiplantae contain high numbers of YTH domain proteins. Here, we performed comprehensive evolutionary analysis of YTH domain proteins and demonstrated that they are highly likely to be actual readers with redundant as well as specific functions. We also show that the ECT2 protein from Arabidopsis thaliana binds to m6A containing RNAs in vivo and that this property relies on the m6A binding pocket carried by its YTH domain. ECT2 is cytoplasmic and relocates to stress granules upon heat exposure, suggesting that it controls mRNA fate in the cytosol. Finally, we demonstrate that ECT2 acts to decode the m6A signal in the trichome and is required for their normal branching through controlling their ploidy levels.
The regulated transport of mRNAs from the cell nucleus to the cytosol is a critical step linking transcript synthesis and processing with translation. However, in plants, only few of the factors that act in the mRNA export pathway have been functionally characterised. Flowering plant genomes encode several members of the ALY protein family, which function as mRNA export factors in other organisms. Arabidopsis thaliana ALY1-4 are commonly detected in root and leaf cells, but are differentially expressed in reproductive tissue. Moreover, the subnuclear distribution of ALY1/2 differs from that of ALY3/4. ALY1 binds with higher affinity to ssRNA than dsRNA and ssDNA, and interacts preferentially with 5-methylcytosine-modified ssRNA. Compared to the full-length protein, the individual RNA recognition motif of ALY1 binds RNA only weakly. ALY proteins interact with the RNA helicase UAP56, indicating a link to the mRNA export machinery. Consistently, ALY1 complements the lethal phenotype of yeast cells lacking the ALY1 orthologue Yra1. Whereas individual aly mutants have a wild-type appearance, disruption of ALY1-4 in 4xaly plants causes vegetative and reproductive defects, including strongly reduced growth, altered flower morphology, as well as abnormal ovules and female gametophytes, causing reduced seed production. Moreover, polyadenylated mRNAs accumulate in the nuclei of 4xaly cells. Our results highlight the requirement of efficient mRNA nucleo-cytosolic transport for proper plant growth and development and indicate that ALY1-4 act partly redundantly in this process; however, differences in expression and subnuclear localisation suggest distinct functions.
5-methylcytosine (m⁵C) is a post-transcriptional RNA modification identified in both stable and highly abundant tRNAs and rRNAs, and in mRNAs. However, its regulatory role in mRNA metabolism is still largely unknown. Here, we reveal that m⁵C modification is enriched in CG-rich regions and in regions immediately downstream of translation initiation sites and has conserved, tissue-specific and dynamic features across mammalian transcriptomes. Moreover, m⁵C formation in mRNAs is mainly catalyzed by the RNA methyltransferase NSUN2, and m⁵C is specifically recognized by the mRNA export adaptor ALYREF as shown by in vitro and in vivo studies. NSUN2 modulates ALYREF's nuclear-cytoplasmic shuttling, RNA-binding affinity and associated mRNA export. Dysregulation of ALYREF-mediated mRNA export upon NSUN2 depletion could be restored by reconstitution of wild-type but not methyltransferase-defective NSUN2. Our study provides comprehensive m⁵C profiles of mammalian transcriptomes and suggests an essential role for m⁵C modification in mRNA export and post-transcriptional regulation.
In plants, protein-coding messenger RNAs (mRNAs) can move via the phloem vasculature to distant tissues, where they may act as non-cell-autonomous signals. Emerging work has identified many phloem-mobile mRNAs, but little is known regarding RNA motifs triggering mobility, the extent of mRNA transport, and the potential of transported mRNAs to be translated into functional proteins after transport. To address these aspects, we produced reporter transcripts harboring transfer RNA (tRNA) - like structures (TLS) that were found to be enriched in the phloem stream and in mRNAs moving over chimeric graft junctions. Phenotypic and enzymatic assays on grafted plants indicated that mRNAs harboring a distinctive TLS can move from transgenic roots into wild-type leaves and from transgenic leaves into wild-type flowers or roots; these mRNAs can also be translated into proteins after transport. In addition, we provide evidence that di-cistronic mRNA:tRNA transcripts are frequently produced in Arabidopsis thaliana and are enriched in the population of graft-mobile mRNAs. Our results suggest that tRNA-derived sequences with predicted stem-bulge-stem-loop structures are sufficient to mediate mRNA transport and seem to be necessary for the mobility of a large number of endogenous transcripts that can move through graft junctions.
The concept that proteins and small RNAs can move to and function in distant body parts is well established. However, non-cell-autonomy of small RNA molecules raises the question: To what extent are protein-coding messenger RNAs (mRNAs) exchanged between tissues in plants? Here we report the comprehensive identification of 2,006 genes producing mobile RNAs in Arabidopsis thaliana. The analysis of variant ecotype transcripts that were present in heterografted plants allowed the identification of mRNAs moving between various organs under normal or nutrient-limiting conditions. Most of these mobile transcripts seem to follow the phloem-dependent allocation pathway transporting sugars from photosynthetic tissues to roots via the vasculature. Notably, a high number of transcripts also move in the opposite, root-to-shoot direction and are transported to specific tissues including flowers. Proteomic data on grafted plants indicate the presence of proteins from mobile RNAs, allowing the possibility that they may be translated at their destination site. The mobility of a high number of mRNAs suggests that a postulated tissue-specific gene expression profile might not be predictive for the actual plant body part in which a transcript exerts its function.
The metazoan TREX complex is recruited to mRNA during nuclear RNA processing and functions in exporting mRNA to the cytoplasm. Nxf1 is an mRNA export receptor, which binds processed mRNA and transports it through the nuclear pore complex. At present, the relationship between TREX and Nxf1 is not understood. Here we show that Nxf1 uses an intramolecular interaction to inhibit its own RNA-binding activity. When the TREX subunits Aly and Thoc5 make contact with Nxf1, Nxf1 is driven into an open conformation, exposing its RNA-binding domain, allowing RNA binding. Moreover, the combined knockdown of Aly and Thoc5 markedly reduces the amount of Nxf1 bound to mRNA in vivo and also causes a severe mRNA export block. Together, our data indicate that TREX provides a license for mRNA export by driving Nxf1 into a conformation capable of binding mRNA.
The Arabidopsis floral meristem-identity genes APETALA1 (AP1) and LEAFY (LFY) confer floral identity on developing floral primordia, whereas TERMINAL FLOWER (TFL) is required to repress their expression within shoot and inflorescence meristems. LFY and AP1 are expressed in floral primordia in response to environmental conditions, such as day length, which regulate the onset of flowering, and presumably also in response to the action of genes that influence flowering time. However, the relationship between these flowering-time genes and the floral meristem-identity genes has been difficult to assess because flowering time is determined by several interacting genetic pathways. Here we describe a method to regulate expression of the flowering-time gene CONSTANS (CO) and demonstrate that CO expression is sufficient to trigger flowering, irrespective of day length. In response to CO expression, transcription of LFY and TFL is initiated rapidly, whereas transcription of AP1 occurs much later. We propose that CO acts within a genetic pathway that is sufficient to activate LFY and TFL transcription, but that rapid activation of AP1 requires an additional pathway.
In metazoans, most pre-messenger RNAs contain introns that are removed by splicing. The spliced mRNAs are then exported to the cytoplasm. Recent studies showed that splicing promotes efficient mRNA export, but the mechanism for coupling these two processes is not known. Here we show that Aly, the metazoan homologue of the yeast mRNA export factor Yralp (ref. 2), is recruited to messenger ribonucleoprotein (mRNP) complexes generated by splicing. In contrast, Aly does not associate with mRNPs assembled on identical mRNAs that already have no introns or with heterogenous nuclear RNP (hnRNP) complexes. Aly is recruited during spliceosome assembly, and then becomes tightly associated with the spliced mRNP. Aly shuttles between the nucleus and cytoplasm, and excess recombinant Aly increases both the rate and efficiency of mRNA export in vivo. Consistent with its splicing-dependent recruitment, Aly co-localizes with splicing factors in the nucleus. We conclude that splicing is required for efficient mRNA export as a result of coupling between the splicing and the mRNA export machineries.
The P19 protein of tomato bushy stunt virus (TBSV) is a multifunctional pathogenicity determinant involved in suppression of posttranscriptional gene silencing, virus movement, and symptom induction. Here, we report that P19 interacts with the conserved RNA-binding domain of an as yet uncharacterized family of plant ALY proteins that, in animals, are involved in export of RNAs from the nucleus and transcriptional coactivation. We show that the four ALY proteins encoded by the Arabidopsis genome and two ALY proteins from Nicotiana benthamiana are localized to the nucleus. Moreover, and in contrast to animal ALY, all but one of the proteins are also in the nucleolus, with distinct subnuclear localizations. Infection of plants by TBSV or expression of P19 from Agrobacterium results in relocation of three of the six ALY proteins from the nucleus to the cytoplasm demonstrating specific targeting of the ALY proteins by P19. The differential effects on subcellular localization indicate that, in plants, the various ALY proteins may have different functions. Interaction with and relocalization of ALY is prevented by mutation of P19 at residues previously shown to be important for P19 function in plants. Down-regulation of expression of two N. benthamiana ALY genes by virus-induced gene silencing did not interfere with posttranscriptional gene silencing. Targeting of ALY proteins during TBSV infection may therefore be related to functions of P19 in addition to its silencing suppression activity.
Post-transcriptional regulation of mRNA mediated by methylation at the N6 position of adenine (N6-methyladenosine (m6A)) has profound effects on transcriptome regulation in plants. Focused studies across eukaryotes offer glimpses into the processes governed by m6A throughout developmental and disease states. However, we lack an understanding of the dynamics and the regulatory potential of m6A during biotic stress in plants. Here, we provide a comprehensive look into the effects of m6A on both the short-term and long-term response to pathogen signaling in Arabidopsis (Arabidopsis thaliana). We demonstrate that m6A-deficient plants are more resistant to bacterial and fungal pathogen infections and have altered immune responses. Furthermore, m6A deposition is specifically coordinated on transcripts involved in defense and immunity prior to and proceeding the pathogen signal flagellin. Consequently, the dynamic modulation of m6A on specific stress-responsive transcripts is correlated with changes in abundance and cleavage of these transcripts. Overall, we show that the m6A methylome is regulated prior to and during simulated and active pathogen stress and functions in the coordination and balancing of normal growth and pathogen responses.
Extreme weather events can cause heat stress that decreases crop production. Recent studies have demonstrated that protein degradation and rRNA homeostasis as well as transcription factors are involved in the thermoresponse in plants. However, how RNA modifications contribute to temperature stress response in plant remains largely unknown. Herein, we identified OsNSUN2 as an RNA 5-methylcytosine (m⁵C) methyltransferase in rice. osnsun2 mutant displayed severe temperature- and light-dependent lesion-mimic phenotypes and heat-stress hypersensitivity. Heat stress enhanced the OsNSUN2-dependent m⁵C modification of mRNAs involved in photosynthesis and detoxification systems, such as β-OsLCY, OsHO2, OsPAL1, and OsGLYI4, which increased protein synthesis. Furthermore, the photosystem of osnsun2 mutant was vulnerable to high ambient temperature and failed to undergo repair under tolerable heat stress. Thus, OsNSUN2 mutation reduced photosynthesis efficiency and accumulated excessive reactive oxygen species upon heat treatment. Our findings demonstrate an important mechanism of mRNA m⁵C-dependent heat acclimation in rice.
The maternal-to-zygotic transition (MZT) is a conserved and fundamental process during which the maternal environment is converted to an environment of embryonic-driven development through dramatic reprogramming. However, how maternally supplied transcripts are dynamically regulated during MZT remains largely unknown. Herein, through genome-wide profiling of RNA 5-methylcytosine (m5C) modification in zebrafish early embryos, we found that m5C-modified maternal mRNAs display higher stability than non-m5C-modified mRNAs during MZT. We discovered that Y-box binding protein 1 (Ybx1) preferentially recognizes m5C-modified mRNAs through p-p interactions with a key residue, Trp45, in Ybx1’s cold shock domain (CSD), which plays essential roles in maternal mRNA stability and early embryogenesis of zebrafish. Together with the mRNA stabilizer Pabpc1a, Ybx1 promotes the stability of its target mRNAs in an m5C-depen- dent manner. Our study demonstrates an unex- pected mechanism of RNA m5C-regulated maternal
mRNA stabilization during zebrafish MZT, highlighting the critical role of m5C mRNA modification in early development.
In plants, transcripts move to distant body parts to potentially act as systemic signals regulating development and growth. Thousands of messenger RNAs (mRNAs) are transported across graft junctions via the phloem to distinct plant parts. Little is known regarding features, structural motifs, and potential base modifications of transported transcripts and how these may affect their mobility. We identified Arabidopsis thaliana mRNAs harboring the modified base 5-methylcytosine (m5C) and found that these are significantly enriched in mRNAs previously described as mobile, moving over graft junctions to distinct plant parts. We confirm this finding with graft-mobile methylated mRNAs TRANSLATIONALLY CONTROLLED TUMOR PROTEIN 1 (TCTP1) and HEAT SHOCK COGNATE PROTEIN 70.1 (HSC70.1), whose mRNA transport is diminished in mutants deficient in m5C mRNA methylation. Together, our results point toward an essential role of cytosine methylation in systemic mRNA mobility in plants and that TCTP1 mRNA mobility is required for its signaling function.
N(6)-Methyladenosine (m(6)A) represents the most prevalent internal modification on mRNA and requires a multicomponent m(6)A methyltransferase complex in mammals. How their plant counterparts determine the global m(6)A modification landscape and its molecular link to plant development remain unknown. Here we show that FKBP12 INTERACTING PROTEIN 37 KD (FIP37) is a core component of the m(6)A methyltransferase complex, which underlies control of shoot stem cell fate in Arabidopsis. The mutants lacking FIP37 exhibit massive overproliferation of shoot meristems and a transcriptome-wide loss of m(6)A RNA modifications. We further demonstrate that FIP37 mediates m(6)A RNA modification on key shoot meristem genes inversely correlated with their mRNA stability, thus confining their transcript levels to prevent shoot meristem overproliferation. Our results suggest an indispensable role of FIP37 in mediating m(6)A mRNA modification, which is required for maintaining the shoot meristem as a renewable source for continuously producing all aerial organs in plants.
In plants small interfering RNAs (siRNA) and micro RNAs move to distant tissues where they control numerous developmental and physiological processes such as morphogenesis and stress responses. Grafting techniques and transient expression systems have been employed to show that sequence-specific siRNAs with a size of 21 to 24 nucleotides traffic to distant organs. We used inverted repeat constructs producing siRNA targeting the meiosis factor DISRUPTED MEIOTIC cDNA 1 (DMC1) and GFP to test whether silencing signals move into meiotically active tissues. In grafted Nicotiana tabacum, a transgenic DMC1 siRNA signal made in source tissues preferably entered the anthers formed in the first flowers. Here, the DMC1 siRNA interfered with meiotic progression and consequently, the flowers were at least partially sterile. In agro-infiltrated Nicotiana benthamiana plants, a GFP siRNA signal produced in leaves was allocated and active in most flower tissues including anthers. In hypocotyl-grafted Arabidopsis thaliana plants, the DMC1 silencing signal consistently appeared in leaves, petioles, and stem, and only a small number of plants displayed DMC1 siRNA signals in flowers. In all three tested plant species the systemic silencing signal penetrated male sporogenic tissues suggesting that plants harbour an endogenous long-distance small RNA transport pathway facilitating siRNA signalling into meiotically active cells.This article is protected by copyright. All rights reserved.
Using a cDNA-array we identified expressed sequence tag 163B24T7 as rapidly up-regulated in Arabidopsis thaliana (L.) Heynh. after pathogen exposure. Detailed expression analysis revealed that the corresponding gene is up-regulated not only after exposure to avirulent Pseudomonas syringae pv. tomato but also to virulent strains. This up-regulation is dependent on functional salicylic acid defence-signalling pathways. Moreover, we found the gene was circadian-regulated, showing peaks of expression at the end of the day. Using plants overexpressing the clock component CCA1, we showed that the PCC1 gene is regulated by the inner clock of Arabidopsis. Accordingly, we named the gene PCC1, for pathogen and circadian controlled. PCC1 is a member of a novel family of six small polypeptides in Arabidopsis. A functional role for PCC1 in plant defence was demonstrated since plants overexpressing PCC1 are resistant against normally virulent oomycetes. Thus, PCC1 demonstrates a potential interrelationship between pathogen and circadian signalling pathways.
Lost in Transit: Long-Distance Trafficking and Phloem Unloading of Protein Signals in Arabidopsis Homografts
- M G Goll
- F Kirpekar
- K A Maggert
- J A Yoder
- C L Hsieh
- X Zhang
- K G Golic
- D S G Paultre
- M P Gustin
- A Molnar
- K J Oparka
Goll, M.G., Kirpekar, F., Maggert, K.A., Yoder, J.A., Hsieh, C.L., Zhang, X., Golic, K.G., Paultre, D.S.G., Gustin, M.P., Molnar, A., and Oparka, K.J. (2016). Lost in Transit: Long-Distance
Trafficking and Phloem Unloading of Protein Signals in Arabidopsis Homografts. Plant Cell 28, 2016-2025.