A small gene family in barley encodes ribosomal proteins homologous to yeast YL17 and L22 from archaebacteria, eubacteria, and chloroplasts

Ribosomal protein NtRPL17 interacts with kinesin-12 family protein NtKRP and functions in the regulation of embryo/seed size and radicle growth

We previously reported that a novel motor protein belonging to the kinesin-12 family, NtKRP, displays critical roles in regulating embryo and seed size establishment. However, it remains unknown exactly how NtKRP contributes to this developmental process. Here, we report that a 60S ribosomal protein NtRPL17 directly interacts with NtKRP. The phenotypes of NtRPL17 RNAi lines show notable embryo and seed size reduction. Structural observations of the NtRPL17-silenced embryos/seeds reveal that the embryo size reduction is due to a decrease in cell number. In these embryos, cell division cycle progression is delayed at the G2/M transition. These phenotypes are similar to that in NtKRP-silenced embryos/seeds, indicating that NtKRP and NtRPL17 function as partners in the same regulatory pathway during seed development and specifically regulate cell cycle progression to control embryo/seed size. This work reveals that NtRPL17, as a widely distributed ribosomal protein, plays a critical role in seed development and provides a new clue in the regulation of seed size. Confirmation of the interaction between NtKRP and NtRPL17 and their co-function in the control of the cell cycle also suggests that the mechanism might be conserved in both plants and animals.

Molecular characterization, immunohistochemical localization and expression of a ribosomal protein L17 gene from Apis cerana cerana

Ribosomal protein L17 (RPL17) is a core protein of the large (60S) ribosomal subunit and plays an important role in protein synthesis. In this report, a RPL17 gene was isolated from Apis cerana cerana, designated as AccRPL17. Alignment analysis showed that AccRPL17 exhibits high homology to other known RPL17s. Moreover, genomic sequence analysis revealed that five exons are splitted by four introns, and the position of the first intron is comparatively conservative, being localized in the 5' untranslated region. Partial putative cis-acting elements related to development were also examined. Quantitative real-time PCR showed that the highest mRNA level was detected in larvae on the fifth day. Simultaneously, immunohistochemical localization showed that AccRPL17 is primarily concentrated in muscular tissues, stigma, body wall, and the surrounding of the eye in the fifth-instar larvae. Further studies suggested that AccRPL17 might be involved in responses to abiotic stresses. This is a report attempting to analyze the expression and distribution of RPL17 in A. cerana cerana. These results indicated that AccRPL17 might play an important role in insect development, and the importance of AccRPL17 in participating in abiotic stresses is discussed.

Dissecting defense-related and developmental transcriptional responses of maize during Ustilago maydis infection and subsequent tumor formation

Infection of maize (Zea mays) plants with the smut fungus Ustilago maydis triggers the formation of tumors on aerial parts in which the fungal life cycle is completed. A differential display screen was performed to gain insight into transcriptional changes of the host response. Some of the genes strongly up-regulated in tumors showed a pronounced developmental expression pattern with decreasing transcript levels from basal to apical shoot segments, suggesting that U. maydis has the capacity to extend the undifferentiated state of maize plants. Differentially expressed genes implicated in secondary metabolism were Bx1, involved in biosynthesis of the cyclic hydroxamic acid 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one, and a novel putative sesquiterpene cyclase gene U. maydis induced (Umi)2. Together with the up-regulation of Umi11 encoding a cyclotide-like protein this suggests a nonconventional induction of plant defenses. Explicitly, U. maydis was resistant to 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one but susceptible to its benzoxazolinone derivative 6-methoxy-2-benzoxazolinone. Infection studies of isolated leaves with U. maydis and Colletotrichum graminicola provided evidence for coregulation of Umi2 and PR-1 gene expression, with mRNA levels strongly determined by the extent of fungal colonization within tissue. However, in contrast to Umi2, transcript levels of PR-1 remained low in plants infected with wild-type U. maydis but were 8-fold elevated upon infection with an U. maydis mutant strongly attenuated in pathogenic development. This suggests that U. maydis colonization in planta suppresses a classical defense response. Furthermore, comparative expression analysis uncovered distinct transcriptional programs operating in the host in response to fungal infection and subsequent tumor formation.

Barley disease resistance gene analogs of the NBS-LRR class: identification and mapping

The majority of verified plant disease resistance genes isolated to date are of the NBS-LRR class, encoding proteins with a predicted nucleotide binding site (NBS) and a leucine-rich repeat (LRR) region. We took advantage of the sequence conservation in the NBS motif to clone, by PCR, gene fragments from barley representing putative disease resistance genes of this class. Over 30 different resistance gene analogs (RGAs) were isolated from the barley cultivar Regatta. These were grouped into 13 classes based on DNA sequence similarity. Actively transcribed genes were identified from all classes but one, and cDNA clones were isolated to derive the complete NBS-LRR protein sequences. Some of the NBS-LRR genes exhibited variation with respect to whether and where particular introns were spliced, as well as frequent premature polyadenylation. DNA sequences related to the majority of the barley RGAs were identified in the recently expanded public rice genomic sequence database, indicating that the rice sequence can be used to extract a large proportion of the RGAs from barley and other cereals. Using a combination of RFLP and PCR marker techniques, representatives of all barley RGA gene classes were mapped in the barley genome, to all chromosomes except 4H. A number of the RGA loci map in the vicinity of known disease resistance loci, and the association between RGA S-120 and the nematode resistance locus Ha2 on chromosome 2H was further tested by co-segregation analysis. Most of the RGA sequences reported here have not been described previously, and represent a useful resource as candidates or molecular markers for disease resistance genes in barley and other cereals.

DNA binding sites recognised in vitro by a knotted class 1 homeodomain protein encoded by the hooded gene, k, in barley (Hordeum vulgare)

The homeodomain of the knotted classes of transcription factors from plants differs from the well characterized Antp/En type homeodomains from Drosophila at key amino acid residues contributing to the DNA binding. A cDNA, Hvh21, derived from the hooded gene and encoding a full length homolog of knotted1 from maize was isolated from barley seedlings and expressed as a maltose binding protein fusion in E. coli. The purified HvH21-fusion protein selected DNA fragments with 1-3 copies of the sequence TGAC. Gel shift experiments showed that the TGAC element was required for binding and the results further indicate that the HvH21-fusion protein binds DNA as a monomer.

Promoter elements controlling developmental and environmental regulation of a tobacco ribosomal protein gene L34

The rpL34 gene, which encodes a cytoplasmic ribosomal protein with a high homology to the rat 60S r-protein L34, was isolated from a genomic library of tobacco (Nicotiana tabacum L. cv. Xanthi-nc). A 1500 bp upstream promoter fragment was fused to the chloramphenicol acetyltransferase (CAT) reporter gene or beta-glucuronidase (GUS) reporter gene and transferred into tobacco plants by the Agrobhacterium-mediated leaf disk transformation method. Analysis of CAT activity in leaf tissues showed that mechanical wounding increased the rpL34 promoter activity about 5 times as compared to untreated controls and that the promoter activity was further enhanced by plant growth regulators, 2,4-dichlorophenoxyacetic acid and benzyladenine. Histochemical GUS staining patterns of the transgenic plants showed that the rpL34 promoter activity is high in actively growing tissues, including various meristems, floral organs, and developing fruits. A series of 5' deletion analyses of the rpL34 promoter indicated that a 50 bp region located between -179 and -129 is essential for wound, auxin and cytokinin responses. Deletion of this region reduced the promoter activity to an undetectable level. Insertion of the 50 nucleotide sequence into a minimal promoter restored the promoter activity and the promoter strength was proportional to the copy number of the upstream sequence. The role of TATA and CAAT box regions was studied by a series of 3' deletion analyses. A 3' deletion up to -28 did not significantly affect the promoter strength. However deletion of the promoter up to 70 bp, which deleted the TATA box region, significantly reduced promoter activity. Further deletion of the promoter up to - 104. eliminating the CAAT box region, abolished the promoter activity. These results suggest that the TATA box and CAAT box regions are also important for the rpL34 promoter activity in addition to the 50 bp upstream region.

The plant translational apparatus

Protein synthesis in both eukaryotic and prokaryotic cells is a complex process requiring a large number of macromolecules: initiation factors, elongation factors, termination factors, ribosomes, mRNA, amino-acylsynthetases and tRNAs. This review focuses on our current knowledge of protein synthesis in higher plants.

The Arabidopsis thaliana ribosomal protein S15 (rig) gene

We have isolated cDNA and genomic clones for Arabidopsis thaliana cytosolic ribosomal protein S15 and determined their sequences. Like animal S15 genes, this plant S15 gene is composed of four exons and the first intron is located immediately following the ATG translational start codon. The 5' end of the S15 mRNA was mapped by RNase protection experiments which showed that this mRNA contains a 5' untranslated region of approx. 83 nucleotides. Southern blot analyses suggest that Arabidopsis S15 is encoded by a small family of genes. The sequences of the predicted exons in the cloned S15 gene are identical to that of the S15 cDNA, demonstrating that this gene is transcriptionally active. Sequence analysis of the cloned A. thaliana S15 gene shows that it is tightly linked (approx. 500 nucleotides distant) to a gene of unknown function. The Arabidopsis S15 protein described here is about 75% identical to vertebrate S15, 70% identical to the homologous yeast protein (S21), 50% identical to archaebacterial S19, 30% identical to eubacterial S19, and about 30% identical to plant mitochondrial and plastid S19.

Characterization of rps17, rp19 and rpl15: three nucleus-encoded plastid ribosomal protein genes

Approximately two-thirds of the 55 to 60 plastid ribosomal proteins are encoded in the nucleus. Since the protein products of each of these genes are needed in equal amounts for ribosome assembly, their expression may be coordinately regulated by common mechanisms. To begin to understand how the expression of these genes is regulated, we have isolated cDNA and genomic clones for three plastid ribosomal protein genes from an Arabidopsis thaliana library. The genes rps17, rpl9 and rpl15, encoding plastid ribosomal proteins CS17, CL9 and CL15, respectively, are located in the nuclear genome and Southern blot data suggest that each is a single copy gene in A. thaliana. Northern blot data show that transcripts from rps17, rpl9 and rpl15 are much more abundant in leaves and stems than they are in roots. The nucleotide sequences of each of these three genes were determined and their transcriptional initiation sites identified. rps17 transcripts have multiple 5' ends suggesting that they are initiated at multiple sites or are post-transcriptionally processed at their 5' end. rpl9 and rpl15 apparently have unique transcriptional initiation sites but are post-transcriptionally processed to remove six and three introns, respectively, from their primary transcripts. We have examined the genomic sequences for motifs that may be important for the proper expression of these genes. A 7 bp sequence motif, whose consensus is 5'-AGGCCCA-3', flanked by AT-rich regions was identified between 38 and 73 nucleotides upstream of the rps17, rpl9 and rpl15 transcriptional initiation sites.