Altered patterns of gene expression in Arabidopsis elicited by cauliflower mosaic virus (CaMV) infection and by a CaMV gene VI transgene

Cauliflower mosaic virus (CaMV) gene VI protein (P6) is an important determinant of symptom expression. Differential display polymerase chain reaction (PCR) was used to identify changes in gene expression in Arabidopsis elicited by a P6 transgene that causes a symptomatic phenotype. We used slot blot hybridization to measure the abundance of mRNAs complementary to 66 candidate PCR products in transgenic, CaMV-infected, and uninfected Arabidopsis plants. CaMV-infected and P6 transgenic plants showed broadly similar changes in abundance of mRNA species. In P6 transgenic plants we detected 18 PCR products that showed unambiguous changes in abundance plus another 15 that showed more limited changes (approximately twofold). CaMV-infected plants showed 17 unambiguous and 13 limited changes. Down-regulated species include those encoding a novel, phenol-like sulfotransferase, and a glycine-rich, RNA-binding protein. Up-regulated species included ones encoding an myb protein, glycine-rich and stress-inducible proteins, and a member of a previously unreported gene family. CaMV infection causes alterations in expression of many Arabidopsis genes. Transgene-mediated expression of P6 mimics virus infection in its effect on host gene expression, providing a potential mechanism for this process.     

Leaf-specific suppression of deoxyhypusine synthase in Arabidopsis thaliana enhances growth without negative pleiotropic effects

Deoxyhypusine synthase (DHS) mediates the first of two enzymatic reactions required for the post-translational activation of eukaryotic translation initiation factor 5A (eIF5A), which in turn is thought to facilitate translation of specific mRNAs. Analyses of GUS activity in transgenic Arabidopsis plants expressing the GUS reporter gene under regulation of the promoter for AtDHS revealed that the expression of DHS changes both spatially and temporally as development progresses. In particular, DHS is expressed not only in rosette leaves, but also in the anthers of developing flowers. To determine the role of DHS in leaves, transgenic plants in which DHS was selectively suppressed in rosettes of Arabidopsis plants were prepared. This was achieved by expressing AtDHS 3'-UTR cDNA as a transgene under regulation of the promoter for AtRbcS2, a gene encoding the small subunit of Rubisco. The dominant phenotypic traits of the DHS-suppressed plants proved to be a dramatic enhancement of both vegetative and reproductive growth. As well, the onset of leaf senescence in the DHS-suppressed plants was delayed by approximately 1 week, but there was no change in the timing of bolting. In addition, there was no evidence for the negative pleiotropic effects, including stunted reproductive growth and reduced seed yield, noted previously for transgenic plants in which DHS was constitutively suppressed. The results indicate that DHS plays a pivotal role in both growth and senescence.     

The arcelin-5 Gene of Phaseolus vulgaris Directs High Seed-Specific Expression in Transgenic Phaseolus acutifolius and Arabidopsis Plants

The regulatory sequences of many genes encoding seed storage proteins have been used to drive seed-specific expression of a variety of proteins in transgenic plants. Because the levels at which these transgene-derived proteins accumulate are generally quite low, we investigated the utility of the arcelin-5 regulatory sequences in obtaining high seed-specific expression in transgenic plants. Arcelin-5 is an abundant seed protein found in some wild common bean (Phaseolus vulgaris L.) genotypes. Seeds of Arabidopsis and Tepary bean (Phaseolus acutifolius A. Gray) plants transformed with arcelin-5 gene constructs synthesized arcelin-5 to levels of 15% and 25% of the total protein content, respectively. To our knowledge, such high expression levels directed by a transgene have not been reported before. The transgenic plants also showed low plant-to-plant variation in arcelin expression. Complex transgene integration patterns, which often result in gene silencing effects, were not associated with reduced arcelin-5 expression. High transgene expression was the result of high mRNA steady-state levels and was restricted to seeds. This indicates that all requirements for high seed-specific expression are cis elements present in the cloned genomic arcelin-5 sequence and trans-acting factors that are available in Arabidopsis and Phaseolus spp., and thus probably in most dicotyledonous plants.     

拟南芥植物硫肽激素-α前体基因AtPSK2的克隆及序列分析

根据拟南芥基因组数据库提供的信息,首次通过聚合酶链反应技术克隆到一个拟南芥硫肽激素-α前体基因——AtPSK2,并对其进行了序列分析。结果表明,所获得的AtPSK2基因是一个长412bp,含有一个内含子和两个没有3’或5’-非转译区的外显子的全编码序列,与数据库提供的序列比较,具有100％的同源性。这一工作将为转基因植物及其细胞培养和育种打下基础．     

Metabolite-binding RNA domains are present in the genes of eukaryotes

Genetic control by metabolite-binding mRNAs is widespread in prokaryotes. These riboswitches are typically located in noncoding regions of mRNA, where they selectively bind their target compound and subsequently modulate gene expression. We have identified mRNA elements in fungi and in plants that match the consensus sequence and structure of thiamine pyrophosphate-binding domains of prokaryotes. In Arabidopsis, the consensus motif resides in the 3'-UTR of a thiamine biosynthetic gene, and the isolated RNA domain binds the corresponding coenzyme in vitro. These results suggest that metabolite-binding mRNAs are possibly involved in eukaryotic gene regulation and that some riboswitches might be representatives of an ancient form of genetic control.     

A miRNA involved in phosphate-starvation response in Arabidopsis

Although microRNAs (miRNAs) have been documented to regulate development in plants and animals , the function of miRNAs in physiology is unclear. miR399 has multiple target sites in the 5' untranslated region (UTR) of a gene encoding a putative ubiquitin-conjugating enzyme (UBC) in Arabidopsis thaliana. We report here that miR399 was highly induced, whereas the target UBC mRNA was reduced by low-phosphate (Pi) stress. In transgenic plants with constitutive expression of miR399, UBC mRNA accumulation was suppressed even under high Pi. The expression of transgene UBC mRNA with 5' UTR miR399 target sites, but not the one without 5' UTR, was reduced under low-Pi condition. Furthermore, transgenic Arabidopsis plants with constitutive expression of miR399 accumulated more Pi than the wild-type, and transgenic plants expressing the UBC mRNA without 5' UTR (miRNA-deregulated) showed less inhibition of primary root growth and less induction of a Pi transporter gene by low-Pi stress than those of wild-type plants. We conclude that miR399 downregulates UBC mRNA accumulation by targeting the 5' UTR, and this regulation is important for plant responses to Pi starvation. The results suggest that miRNAs have functional roles for plants to cope with fluctuations in mineral-nutrient availability in the soil.     

Comparative analysis of sequences preceding protein-coding mitochondrial genes in flowering plants

We examined the nucleotide sequences preceding 23 mitochondrial protein-coding genes held in common by maize, rice, wheat, sugar beet, tobacco, Arabidopsis, and Brassica to look for features related to translation initiation and to assess the degree of conservation in mitochondrial mRNA leaders among these plants. We observed broad variation in sequence similarity as illustrated by dot plot analysis, ranging from a level rivaling that of coding sequences to complete absence of homology due to lineage-specific DNA rearrangements. Genes encoding ATP synthase subunits predominated in the latter category, whereas ones encoding cytochrome c biogenesis proteins and NADH dehydrogenase subunits were primarily of the highly conserved type. Within the region immediately preceding initiation codons, in most cases we did not observe motifs consistent with a bacterial-type Shine-Dalgarno interaction to assist in ribosome binding, nor was any other consensus sequence evident. In fact, indels in the form of tandem repeats were seen among homologues from different plants. We did, however, observe a bias for high adenosine and low cytosine in the proximal approximately 30 nt compared with further upstream. Duplicates of some sequences in our data set were found to be associated with more than one gene within a genome. Indeed, 3 such families of upstream cassettes were identified, and they exhibit a lineage-specific distribution among plants. Moreover, the presence of related sequences at genomic sites distant from known genes raises the possibility of future recruitment as regulatory elements. Our observations point to a dynamic nature in the makeup of the 5' leaders of plant mitochondrial mRNAs and an apparent plasticity in translational control elements.