mRNAs In Arabidopsis Research Articles

Transcriptome-wide profiling of RNA N4-cytidine acetylation in Arabidopsis thaliana and Oryza sativa

Acetylation of N4-cytidine (ac4C) has recently been discovered as a novel modification of mRNA. RNA ac4C modification has been shown to be a key regulator of RNA stability, RNA translation, and the thermal stress response. However, its existence in eukaryotic mRNAs is still controversial. In plants, the existence, distribution pattern, and potential function of RNA ac4C modification are largely unknown. Here we report the presence of ac4C in the mRNAs of both Arabidopsis thaliana and rice (Oryza sativa). By comparing two ac4C sequencing methods, we found that RNA immunoprecipitation and sequencing (acRIP-seq), but not ac4C sequencing, was suitable for plant RNA ac4C sequencing. We present transcriptome-wide atlases of RNA ac4C modification in A. thaliana and rice mRNAs obtained by acRIP-seq. Analysis of the distribution of RNA ac4C modifications showed that ac4C is enriched near translation start sites in rice mRNAs and near translation start sites and translation end sites in Arabidopsis mRNAs. The RNA ac4C modification level is positively correlated with RNA half-life and the number of splicing variants. Similar to that in mammals, the translation efficiency of ac4C target genes is significantly higher than that of other genes. Our in vitro translation results confirmed that RNA ac4C modification enhances translation efficiency. We also found that RNA ac4C modification is negatively correlated with RNA structure. These results suggest that ac4C is a conserved mRNA modification in plants that contributes to RNA stability, splicing, translation, and secondary structure formation.

Arabidopsis mRNA decay landscape shaped by XRN 5'-3' exoribonucleases.

5'-3' exoribonucleases (XRNs) play crucial roles in the control of RNA processing, quality, and quantity in eukaryotes. Although genome-wide profiling of RNA decay fragments is now feasible, how XRNs shape the plant mRNA degradome remains elusive. Here, we profiled and analyzed the RNA degradomes of Arabidopsis wild-type and mutant plants with defects in XRN activity. Deficiency of nuclear XRN3 or cytoplasmic XRN4 activity but not nuclear XRN2 activity greatly altered Arabidopsis mRNA decay profiles. Short excised linear introns and cleaved pre-mRNA fragments downstream of polyadenylation sites were polyadenylated and stabilized in the xrn3 mutant, demonstrating the unique function of XRN3 in the removal of cleavage remnants from pre-mRNA processing. Further analysis of stabilized XRN3 substrates confirmed that pre-mRNA 3' end cleavage frequently occurs after adenosine. The most abundant decay intermediates in wild-type plants include not only the primary substrates of XRN4 but also the products of XRN4-mediated cytoplasmic decay. An increase in decay intermediates with 5' ends upstream of a consensus motif in the xrn4 mutant suggests that there is an endonucleolytic cleavage mechanism targeting the 3' untranslated regions of many Arabidopsis mRNAs. However, analysis of decay fragments in the xrn4 mutant indicated that, except for microRNA-directed slicing, endonucleolytic cleavage events in the coding sequence rarely result in major decay intermediates. Together, these findings reveal the major substrates and products of nuclear and cytoplasmic XRNs along Arabidopsis transcripts and provide a basis for precise interpretation of RNA degradome data.

The SnRK1-eIFiso4G1 signaling relay regulates the translation of specific mRNAs in Arabidopsis under submergence.

Cellular responses to oxygen deprivation are essential for survival during energy crises in plants and animals. Hypoxia caused by submergence results in reprogramming of translation dynamic in plants, but the molecular mechanisms are not well understood. Here we show that Arabidopsis Snf1-related protein kinase 1 (SnRK1) phosphorylates the translation initiation factor eIFiso4G to regulate translation dynamic under submergence. In Arabidopsis, there are two eIFiso4G genes, eIFiso4G1 and eIFiso4G2, which belong to the eIF4G family. Both eIFiso4Gs were phosphorylated by SnRK1 under submergence. Interestingly, the eIFiso4G1 knockout mutant, but not the eIFiso4G2 mutant, became more sensitive to submergence, implying that eIFiso4G1 is involved in regulating submergence tolerance in Arabidopsis. Comparison of RNA sequences in the polysome fraction and the RNAs immunoprecipitated by eIFiso4G1 from Col-0 and the SnRK1 and eIFiso4G1 mutants revealed that lack of eIFiso4G1 phosphorylation disrupts the translation of specific mRNAs under submergence. Taken together, our findings suggest that the SnRK1-eIFiso4G1 relay controls the translation of an array of genes under hypoxia, including core hypoxia response genes and genes related to stress response and biosynthetic process.

N6-Methyladenosine Inhibits Local Ribonucleolytic Cleavage to Stabilize mRNAs in Arabidopsis

N6-methyladenosine (m6A) is a dynamic, reversible, covalently modified ribonucleotide that occurs predominantly toward 3' ends of eukaryotic mRNAs and is essential for their proper function and regulation. In Arabidopsis thaliana, many RNAs contain at least one m6A site, yet the transcriptome-wide function of m6A remains mostly unknown. Here, we show that many m6A-modified mRNAs in Arabidopsis have reduced abundance in the absence of this mark. The decrease in abundance is due to transcript destabilization caused by cleavage occurring 4 or 5 nt directly upstream of unmodified m6A sites. Importantly, we also find that, upon agriculturally relevant salt treatment, m6A is dynamically deposited on and stabilizes transcripts encoding proteins required for salt andosmotic stress response. Overall, our findings reveal that m6A generally acts as a stabilizing mark throughinhibition of site-specific cleavage in plant transcriptomes, and this mechanism is required forproper regulation of the salt-stress-responsive transcriptome.

Two Arabidopsis late pollen transcripts are detected in cytoplasmic granules.

Many of mRNAs synthesized during pollen development are translated after germination, and we hypothesize that they are stored in cytoplasmic granules. We analyzed the cellular localization of the SKS14 and AT59 Arabidopsis mRNAs, which are orthologues of the tobacco NTP303 and tomato LAT59 pollen mRNAs, respectively, by artificially labeling the transcripts with a MS2‐GFP chimera. A MATLAB‐automated image analysis helped to identify the presence of cytoplasmic SKS14 and AT59 mRNA granules in mature pollen grains. These mRNA granules partially colocalized with VCS and DCP1, two processing body (PB) proteins. Finally, we found a temporal correlation between SKS14 protein accumulation and the disappearance of SKS14 mRNA granules during pollen germination. These results contribute to unveil a mechanism for translational regulation in Arabidopsis thaliana pollen.

Transcriptome-Wide Mapping of RNA 5-Methylcytosine in Arabidopsis mRNAs and Noncoding RNAs.

Posttranscriptional methylation of RNA cytosine residues to 5-methylcytosine (m5C) is an important modification with diverse roles, such as regulating stress responses, stem cell proliferation, and RNA metabolism. Here, we used RNA bisulfite sequencing for transcriptome-wide quantitative mapping of m5C in the model plant Arabidopsis thaliana We discovered more than a thousand m5C sites in Arabidopsis mRNAs, long noncoding RNAs, and other noncoding RNAs across three tissue types (siliques, seedling shoots, and roots) and validated a number of these sites. Quantitative differences in methylated sites between these three tissues suggest tissue-specific regulation of m5C. Perturbing the RNA m5C methyltransferase TRM4B resulted in the loss of m5C sites on mRNAs and noncoding RNAs and reduced the stability of tRNAAsp(GTC) We also demonstrate the importance of m5C in plant development, as trm4b mutants have shorter primary roots than the wild type due to reduced cell division in the root apical meristem. In addition, trm4b mutants show increased sensitivity to oxidative stress. Finally, we provide insights into the targeting mechanism of TRM4B by demonstrating that a 50-nucleotide sequence flanking m5C C3349 in MAIGO5 mRNA is sufficient to confer methylation of a transgene reporter in Nicotiana benthamiana.

Uridylation and PABP Cooperate to Repair mRNA Deadenylated Ends in Arabidopsis.

Uridylation emerges as a key modification promoting mRNA degradation in eukaryotes. In addition, uridylation by URT1 prevents the accumulation of excessively deadenylated mRNAs in Arabidopsis. Here, we show that the extent of mRNA deadenylation is controlled by URT1. By using TAIL-seq analysis, we demonstrate the prevalence of mRNA uridylation and the existence, at lower frequencies, of mRNA cytidylation and guanylation in Arabidopsis. Both URT1-dependent and URT1-independent types of uridylation co-exist but only URT1-mediated uridylation prevents the accumulation of excessively deadenylated mRNAs. Importantly, uridylation repairs deadenylated extremities to restore the size distribution observed for non-uridylated oligo(A) tails. In vivo and in vitro data indicate that Poly(A) Binding Protein (PABP) binds to uridylated oligo(A) tails and determines the length of U-extensions added by URT1. Taken together, our results uncover a role for uridylation and PABP in repairing mRNA deadenylated ends and reveal that uridylation plays diverse roles in eukaryotic mRNA metabolism.

Complex Processing Patterns of mRNAs of the Large ATP Synthase Operon in Arabidopsis Chloroplasts

Chloroplasts are photosynthetic cell organelles which have evolved from endosymbiosis of the cyanobacterial ancestor. In chloroplasts, genes are still organized into transcriptional units as in bacteria but the corresponding poly-cistronic mRNAs undergo complex processing events, including inter-genic cleavage and 5′ and 3′ end-definition. The current model for processing proposes that the 3′ end of the upstream cistron transcripts and the 5′ end of the downstream cistron transcripts are defined by the same RNA-binding protein and overlap at the level of the protein-binding site.We have investigated the processing mechanisms that operate within the large ATP synthase (atp) operon, in Arabidopsis thaliana chloroplasts. This operon is transcribed by the plastid-encoded RNA polymerase starting from two promoters, which are upstream and within the operon, respectively, and harbors four potential sites for RNA-binding proteins. In order to study the functional significance of the promoters and the protein-binding sites for the maturation processes, we have performed a detailed mapping of the atp transcript ends. Our data indicate that in contrast to maize, atpI and atpH transcripts with overlapping ends are very rare in Arabidopsis. In addition, atpA mRNAs, which overlap with atpF mRNAs, are even truncated at the 3′ end, thus representing degradation products. We observe, instead, that the 5′ ends of nascent poly-cistronic atp transcripts are defined at the first protein-binding site which follows either one of the two transcription initiation sites, while the 3′ ends are defined at the subsequent protein-binding sites or at hairpin structures that are encountered by the progressing RNA polymerase. We conclude that the overlapping mechanisms of mRNA protection have only a limited role in obtaining stable processed atp mRNAs in Arabidopsis. Our findings suggest that during evolution of different plant species as maize and Arabidopsis, chloroplasts have evolved multiple strategies to produce mature transcripts suitable for translation.

Uridylation prevents 3' trimming of oligoadenylated mRNAs

Degradation of mRNAs is usually initiated by deadenylation, the shortening of long poly(A) tails to oligo(A) tails of 12–15 As. Deadenylation leads to decapping and to subsequent 5′ to 3′ degradation by XRN proteins, or alternatively 3′ to 5′ degradation by the exosome. Decapping can also be induced by uridylation as shown for the non-polyadenylated histone mRNAs in humans and for several mRNAs in Schizosaccharomyces pombe and Aspergillus nidulans. Here we report a novel role for uridylation in preventing 3′ trimming of oligoadenylated mRNAs in Arabidopsis. We show that oligo(A)-tailed mRNAs are uridylated by the cytosolic UTP:RNA uridylyltransferase URT1 and that URT1 has no major impact on mRNA degradation rates. However, in absence of uridylation, oligo(A) tails are trimmed, indicating that uridylation protects oligoadenylated mRNAs from 3′ ribonucleolytic attacks. This conclusion is further supported by an increase in 3′ truncated transcripts detected in urt1 mutants. We propose that preventing 3′ trimming of oligo(A)-tailed mRNAs by uridylation participates in establishing the 5′ to 3′ directionality of mRNA degradation. Importantly, uridylation prevents 3′ shortening of mRNAs associated with polysomes, suggesting that a key biological function of uridylation is to confer 5′ to 3′ polarity in case of co-translational mRNA decay.

RNA PROCESSING FACTOR3 Is Crucial for the Accumulation of MatureccmCTranscripts in Mitochondria of Arabidopsis Accession Columbia

RNA PROCESSING FACTOR1 (RPF1) and RPF2 are pentatricopeptide repeat (PPR) proteins involved in 5' processing of different mitochondrial mRNAs in Arabidopsis (Arabidopsis thaliana). Both factors are highly similar to RESTORERS OF FERTILITY (RF), which are part of cytoplasmic male sterility/restoration systems in various plant species. These findings suggest a predominant role of RF-like PPR proteins in posttranscriptional 5' processing. To further explore the functions of this group of proteins, we examined a number of T-DNA lines carrying insertions in the corresponding PPR genes. This screening identified a nearly complete absence of mature ccmC transcripts in an At1g62930 T-DNA insertion line, a phenotype that could be restored by the introduction of the intact At1g62930 gene into the mutant. The insertion in this nuclear gene, which we now call RPF3, also leads to a severe reduction of the CcmC protein in mitochondria. The analysis of C24/rpf3-1 F2 hybrids lacking functional RPF3 genes revealed that this gene has less influence on the generation of the mature ccmC 5' transcript end derived from a distinct ccmC 5' upstream configuration found in mitochondrial DNAs from C24 and other accessions. These data show that a particular function of an RF-like protein is required only in connection with a distinct mtDNA configuration. Our new results further substantiate the fundamental role of RF-like PPR proteins in the posttranscriptional generation of plant mitochondrial 5' transcript termini.

Evidence for Antisense Transcription Associated with MicroRNA Target mRNAs in Arabidopsis

Antisense transcription is a pervasive phenomenon, but its source and functional significance is largely unknown. We took an expression-based approach to explore microRNA (miRNA)-related antisense transcription by computational analyses of published whole-genome tiling microarray transcriptome and deep sequencing small RNA (smRNA) data. Statistical support for greater abundance of antisense transcription signatures and smRNAs was observed for miRNA targets than for paralogous genes with no miRNA cleavage site. Antisense smRNAs were also found associated with MIRNA genes. This suggests that miRNA-associated “transitivity” (production of small interfering RNAs through antisense transcription) is more common than previously reported. High-resolution (3 nt) custom tiling microarray transcriptome analysis was performed with probes 400 bp 5′ upstream and 3′ downstream of the miRNA cleavage sites (direction relative to the mRNA) for 22 select miRNA target genes. We hybridized RNAs labeled from the smRNA pathway mutants, including hen1-1, dcl1-7, hyl1-2, rdr6-15, and sgs3-14. Results showed that antisense transcripts associated with miRNA targets were mainly elevated in hen1-1 and sgs3-14 to a lesser extent, and somewhat reduced in dcl11-7, hyl11-2, or rdr6-15 mutants. This was corroborated by semi-quantitative reverse transcription PCR; however, a direct correlation of antisense transcript abundance in MIR164 gene knockouts was not observed. Our overall analysis reveals a more widespread role for miRNA-associated transitivity with implications for functions of antisense transcription in gene regulation. HEN1 and SGS3 may be links for miRNA target entry into different RNA processing pathways.

Computational identification of condition-specific miRNA targets based on gene expression profiles and sequence information

BackgroundMicroRNAs (miRNAs) are small and noncoding RNAs that play important roles in various biological processes. They regulate target mRNAs post-transcriptionally through complementary base pairing. Since the changes of miRNAs affect the expression of target genes, the expression levels of target genes in specific biological processes could be different from those of non-target genes. Here we demonstrate that gene expression profiles contain useful information in separating miRNA targets from non-targets.ResultsThe gene expression profiles related to various developmental processes and stresses, as well as the sequences of miRNAs and mRNAs in Arabidopsis, were used to determine whether a given gene is a miRNA target. It is based on the model combining the support vector machine (SVM) classifier and the scoring method based on complementary base pairing between miRNAs and mRNAs. The proposed model yielded low false positive rate and retrieved condition-specific candidate targets through a genome-wide screening.ConclusionOur approach provides a novel framework into screening target genes by considering the gene regulation of miRNAs. It can be broadly applied to identify condition-specific targets computationally by embedding information of gene expression profiles.

On the functions of the h subunit of eukaryotic initiation factor 3 in late stages of translation initiation

Reporter transgene assays and comparative polysome-microarray analysis reveal that the intact h subunit of Arabidopsis eIF3 contributes to efficient translation initiation on mRNA leader sequences harbouring multiple uORFs.

LEAFY COTYLEDON 2 activation is sufficient to trigger the accumulation of oil and seed specific mRNAs in Arabidopsis leaves

LEAFY COTYLEDON 2 ( LEC2) is a key regulator of seed maturation in Arabidopsis. To unravel some of its complex pleiotropic functions, analyses were performed with transgenic plants expressing an inducible LEC2:GR protein. The chimeric protein is functional and can complement lec2 mutation. Interestingly, the induction of LEC2 leads to the accumulation of storage oil in leaves. In addition, short-term induction and use of translation inhibitors allowed to demonstrate that LEC2 can directly trigger the accumulation of seed specific mRNAs. Consistent with these results, the expression of three other major seed regulators namely, LEC1, FUS3, and ABI3 were also induced by LEC2 activation.

Circadian Control of Messenger RNA Stability. Association with a Sequence-Specific Messenger RNA Decay Pathway

Transcriptional and posttranscriptional regulation are well-established mechanisms for circadian gene expression. Among the latter, differential messenger RNA (mRNA) stability has been hypothesized to control gene expression in response to the clock. However, direct proof that the rate of mRNA turnover can be regulated by the clock is lacking. Previous microarray expression data for unstable mRNAs in Arabidopsis (Arabidopsis thaliana) revealed that mRNA instability is associated with a group of genes controlled by the circadian clock. Here, we show that CCR-LIKE (CCL) and SENESCENCE ASSOCIATED GENE 1 transcripts are differentially regulated at the level of mRNA stability at different times of day. In addition, the changes in CCL mRNA stability continue under free-running conditions, indicating that it is controlled by the Arabidopsis circadian clock. Furthermore, we show that these mRNAs are targets of the mRNA degradation pathway mediated by the downstream (DST) instability determinant. Disruption of the DST-mediated decay pathway in the dst1 mutant leads to aberrant circadian mRNA oscillations that correlate with alterations of the half-life of CCL mRNA relative to parental plants in the morning and afternoon. That this is due to an effect on the circadian control is evidenced by mRNA decay experiments carried out in continuous light. Finally, we show that the defects exhibited by dst mutants are reflected by an impact on circadian regulation at the whole plant level. Together, these results demonstrate that regulation of mRNA stability is important for clock-controlled expression of specific genes in Arabidopsis. Moreover, these data uncover a connection between circadian rhythms and a sequence-specific mRNA decay pathway.

Endogenous trans-Acting siRNAs Regulate the Accumulation of Arabidopsis mRNAs

Here we describe a set of endogenous short interfering RNAs (siRNAs) in Arabidopsis, some of which direct the cleavage of endogenous mRNAs. These siRNAs correspond to both sense and antisense strands of a noncoding RNA (At2g27400) that apparently is converted to double-stranded RNA and then processed in 21 nt increments. These siRNAs differ from previously described regulatory small RNAs in two respects. First, they require components of the cosuppression pathway (RDR6 and SGS3) and also components of the microRNA (miRNA) pathway (AGO1, DCL1, HEN1, and HYL1) but not components needed for heterochromatic siRNAs (DCL3 and RDR2), another class of endogenous plant siRNAs. Second, these siRNAs repress the expression of genes that have little overall resemblance to the genes from which they originate, a characteristic previously reported only for miRNAs. The identification of this silencing pathway provides yet another dimension to posttranscriptional mRNA regulation in plants.

Novel alternative splicing of mRNAs encoding poly(A) polymerases in Arabidopsis

The Arabidopsis thaliana genome possesses four genes whose predicted products are similar to eukaryotic poly(A) polymerases from yeasts and animals. These genes are all expressed, as indicated by RT/PCR and Northern blot analysis. The four Arabidopsis PAPs share a conserved N-terminal catalytic core with other eukaryotic enzymes, but differ substantially in their C-termini. Moreover, one of the four Arabidopsis enzymes is significantly shorter than the other three, and is more divergent even within the conserved core of the protein. Nonetheless, the protein encoded by this gene, when produced in and purified from E. coli, possesses nonspecific poly(A) polymerase activity. Genes encoding these Arabidopsis PAPs give rise to a number of alternatively spliced mRNAs. While the specific nature of the alternative splicing varied amongst these three genes, mRNAs from the three “larger” genes could be alternatively spliced in the vicinity of the 5th and 6th introns of each gene. Interestingly, the patterns of alternative splicing vary in different tissues. The ubiquity of alternative splicing in this gene family, as well as the differences in specific mechanisms of alternative processing in the different genes, suggests an important function for alternatively spliced PAP mRNAs in Arabidopsis.

Translational polymorphism as a potential source of plant proteins variety in Arabidopsis thaliana.

According to scanning model, 40S ribosomal subunits can either initiate translation at start AUG codon in suboptimal context or miss it and initiate translation at downstream AUG(s), thereby producing several proteins. Functional significance of such a protein translational polymorphism is still unknown. We compared predicted subcellular localizations of annotated Arabidopsis thaliana proteins and their potential N-terminally truncated forms started from the nearest downstream in-frame AUG codons. It was found that localizations of full and N-truncated proteins differ in many cases: 12.2% of N-truncated proteins acquired sorting signals de novo and 5.7% changed their predicted subcellular locations (mitochodria, chloroplast or secretory pathway). It is likely that the in-frame downstream AUGs may be frequently utilized to synthesize proteins possessing new functional properties and such a translational polymorphism may serve as an important source of cellular and organelle proteomes.

Molecular characterization of a novel lipase-like pathogen-inducible gene family of Arabidopsis.

In a differential screening between Arabidopsis plants pretreated with the resistance-inducer beta-aminobutyric acid and untreated control plants, we have identified a gene encoding a novel lipase-like protein, PRLIP1. The abundance of PRLIP1 mRNAs in Arabidopsis leaves was up-regulated by application of beta-aminobutyric acid, salicylic acid (SA), and ethylene as well as by various pathogens. Induction of PRLIP1 depended on a functioning SA and ethylene signal transduction pathway but was independent of jasmonate signaling. This novel pathogenesis-related (PR) gene of Arabidopsis belongs to a gene family consisting of six (PRLIP1, PRLIP2, PRLIP4, PRLIP5, PRLIP6, and PRLIP7) closely related members in tandem position on chromosome 5. Among these genes, PRLIP2 also was induced in leaves by SA and infections by pathogens but on a much lower level than PRLIP1. The PRLIP1 family showed a tissue-specific expression pattern. Both PRLIP1 and PRLIP2 were specifically expressed in leaves and siliques, PRLIP1 additionally in stems and flowers. The expression of PRLIP6 and PRLIP4 was root specific, whereas mRNA of PRLIP5 and PRLIP7 were not detected in any of these tissues. The more distantly related genes PRLIP3, PRLIP9, and PRLIP8 were found on chromosomes 2, 4, and 5, respectively. The expression level of PRLIP3 was checked and found constitutive during the different stress conditions tested. The PRLIP1 gene was overexpressed in Escherichia coli, and the resulting PRLIP1 protein showed esterase activity on p-nitrophenyl-butyrate and allowed the growth of the bacteria on lipidic substrates such as Tween20 or Tween80.

Ubiquitin extension proteins of Arabidopsis thaliana. Structure, localization, and expression of their promoters in transgenic tobacco.

The highly conserved protein ubiquitin is synthesized in eukaryotes as two types of protein fusions from which active ubiquitin is derived by proteolytic processing. We report here the isolation and characterization of multiple genes from one type that encode ubiquitin extension proteins from the higher plant, Arabidopsis thaliana (L.). Two genes with 90% nucleotide identity in their exons encode ubiquitin and identical 52-amino acid (aa) extension proteins with 85 and 79% aa identity to 52-aa extension proteins from humans and yeast, respectively. Two other genes with 90% nucleotide identity encode ubiquitin and 81-aa extension proteins that differ by 4 amino acids from each other and are approximately 70% identical to the 76- and the 80-aa extension proteins from yeast and humans, respectively. Antibodies recognizing the 52- and 81-aa Arabidopsis extension proteins identify them as constituents of ribosomes. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the 52- and 81-aa extension proteins migrate at 6.8 and 11.5 kDa, respectively, and neither cross-reacts with anti-ubiquitin antibodies, indicating that extension proteins are cleaved from ubiquitin following translation. Ubiquitin extension protein genes encode the smallest transcript size class of ubiquitin mRNAs in Arabidopsis. The 5'-flanking regions of both UBQ1 and UBQ6, genes representative of the both extension proteins, direct the expression of readily detectable levels of the marker enzyme beta-glucuronidase in transgenic tobacco, suggesting the utility of these promoters for expression of foreign genes in higher plants.