Promoter analysis of seed storage protein genes from Canavalia gladiata D.C

A reference genome for pea provides insight into legume genome evolution

We report the first annotated chromosome-level reference genome assembly for pea, Gregor Mendel's original genetic model. Phylogenetics and paleogenomics show genomic rearrangements across legumes and suggest a major role for repetitive elements in pea genome evolution. Compared to other sequenced Leguminosae genomes, the pea genome shows intense gene dynamics, most likely associated with genome size expansion when the Fabeae diverged from its sister tribes. During Pisum evolution, translocation and transposition differentially occurred across lineages. This reference sequence will accelerate our understanding of the molecular basis of agronomically important traits and support crop improvement.

Temporal and spatial control of gene expression in horticultural crops

Biotechnology provides plant breeders an additional tool to improve various traits desired by growers and consumers of horticultural crops. It also provides genetic solutions to major problems affecting horticultural crops and can be a means for rapid improvement of a cultivar. With the availability of a number of horticultural genome sequences, it has become relatively easier to utilize these resources to identify DNA sequences for both basic and applied research. Promoters play a key role in plant gene expression and the regulation of gene expression. In recent years, rapid progress has been made on the isolation and evaluation of plant-derived promoters and their use in horticultural crops, as more and more species become amenable to genetic transformation. Our understanding of the tools and techniques of horticultural plant biotechnology has now evolved from a discovery phase to an implementation phase. The availability of a large number of promoters derived from horticultural plants opens up the field for utilization of native sequences and improving crops using precision breeding. In this review, we look at the temporal and spatial control of gene expression in horticultural crops and the usage of a variety of promoters either isolated from horticultural crops or used in horticultural crop improvement.

Isolation and functional characterization of a novel seed-specific promoter region from peanut

The importance of using tissue-specific promoters in the genetic transformation of plants has been emphasized increasingly. Here, we report the isolation of a novel seed-specific promoter region from peanut and its validation in Arabidopsis and tobacco seeds. The reported promoter region referred to as groundnut seed promoter (GSP) confers seed-specific expression in heterologous systems, which include putative promoter regions of the peanut (Arachis hypogaea L.) gene 8A4R19G1. This region was isolated, sequenced, and characterized using gel shift assays. Tobacco transgenics obtained using binary vectors carrying uidA reporter gene driven by GSP and/or cauliflower mosaic virus 35S promoters were confirmed through polymerase chain reaction (PCR), RT-PCR, and computational analysis of motifs which revealed the presence of TATA, CAAT boxes, and ATG signals. This seed-specific promoter region successfully targeted the reporter uidA gene to seed tissues in both Arabidopsis and tobacco model systems, where its expression was confirmed by histochemical analysis of the transgenic seeds. This promoter region is routinely being used in the genetic engineering studies in legumes aimed at targeting novel transgenes to the seeds, especially those involved in micronutrient enhancement, fungal resistance, and molecular pharming.

Functional analysis of the Arabidopsis thaliana poly(A) binding protein PAB5 gene promoter in Nicotiana tabacum

Poly(A) binding (PAB) proteins play an important role in posttranscriptional regulation by stabilizing mRNA and initiating translation in eukaryotes. Previous studies have shown that the expression of PAB5 gene encoding one of the poly(A) binding proteins (PABPs) in Arabidopsis thaliana is restricted to pollen, ovule and early embryogenesis. To investigate the tissue-specific expression of the PAB5 promoter, a series of promoter deletions (from -1,804, -1,653, -1,334, -1,014, -715, -424 and -175 to +185) were fused to the uidA reporter gene (GUS) and transformed into tobacco plants (Nicotiana tabacum L.). The results showed that GUS expression driven by the full-length PAB5 promoter was detected in floral organs (pollen, ovule, anther, stigma) and immature seeds, but not in vegetative tissues (root, stem, leaf) and mature seeds. Deletion analysis of the PAB5 promoter region revealed that promoters longer than -1,334 had the similar GUS expression level in pollen, ovule and immature seeds, whereas further 5' deletions resulted in a considerable reduction in GUS activity. These results indicated that the region between -1,653 and -1,014 was necessary to direct the tissue-specific expression of PAB5 promoter during development.

Analysis of pea HMG-I/Y expression suggests a role in defence gene regulation

SUMMARY HMG-I/Y proteins are characterized by the presence of AT-hook motifs, DNA binding domains that recognize AT-rich tracts of DNA. By facilitating protein:protein and protein:DNA interactions in the vicinity of these AT-rich binding sites, HMG-I/Y positively or negatively regulates gene expression. Several pea defence gene promoters have AT-rich tracts of DNA that are potential targets for modulation via HMG-I/Y. In this study, a comparison of the expression of a pea defence gene (DRR206) mRNA relative to the expression of HMG-I/Y mRNA was monitored by Northern analysis following the inoculation of a fungal pathogen, Fusarium solani or treatment with chitosan and a F. solani DNase (Fsph DNase). In pea pod endocarp tissue, HMG-I/Y expression was observed at high levels in untreated tissue and at lower levels 6 h following inoculation or wounding of the tissue. Western blots with an antipea HMG-I/Y polyclonal antibody also revealed that pea HMG-I/Y is expressed at decreased levels 6 h following inoculation or elicitor treatment. HMG-I/Y extracted from pea caused alterations in the gel migration of radio-labelled AT-rich sequences from the pea DRR206 promoter, suggesting that similar interactions could exist in vivo. Agroinfiltration was utilized to express the pea HMG-I/Y gene in tobacco containing a chimeric gene fusion of a promoter from the PR gene, DRR206, and the beta-glucuronidase (GUS) reporter gene. Transient expression of pea HMG-I/Y led to a decrease in GUS reporter gene activity in the heterologous tobacco system. These data implicate pea HMG-I/Y abundance in the down-regulation of DRR206 gene expression, and possibly HMG-I/Y depletion in the expression of defence genes in pea.

Regulation of gene expression of a cysteine proteinase, EP-C1, by a VIVIPAROUS1-like factor from common bean

A VIVIPAROUS1-like transcription factor, PvALF, is known to activate storage protein genes through the RY element in their promoters in maturing common bean seeds. This element also exists in the promoter of the gene for a cysteine proteinase, EP-C1, which is expressed in a germination-specific manner. We show that the EP-C1 gene expression is suppressed through interaction of PvALF with the RY element in the EP-C1 promoter.

A TGACGT motif in the 5'-upstream region of alpha-amylase gene from Vigna mungo is a cis-element for expression in cotyledons of germinated seeds

Alpha-amylase is expressed at high levels in cotyledons of germinated seeds of Vigna mungo. The mRNA for alpha-amylase appeared in cotyledons of the seeds at 1 d after imbibition started (DAI). Two TGACGT motifs at -445 and at -125 in the promoter region of the gene interacted with nuclear proteins from cotyledons of dry seeds and the activities were detected until 3 DAI. A transient assay with particle bombardment showed that the downstream region from -135 in the promoter was required for high level expression in the cotyledons and the activity was reduced by mutation of the TGACGT motif at -125. The activities to bind the TGACGT motifs were detected in the axes of the seeds at 1 DAI but disappeared at 4 DAI, although the mRNA for alpha-amylase in the axes appeared at 4 DAI and increased in level by 6 DAI. A transient assay experiment showed that a positive regulatory element for the expression in the axes was located in the region from -630 to -453. These results indicated that the TGACGT motif at -125 was required for high level expression of the gene in the cotyledons of the germinated seeds.

Cloning and molecular analyses of a gibberellin 20-oxidase gene expressed specifically in developing seeds of watermelon

To understand the biosynthesis and functional role of gibberellins (GAs) in developing seeds, we isolated Cv20ox, a cDNA clone from watermelon (Citrullus lanatus) that shows significant amino acid homology with GA 20-oxidases. The complementary DNA clone was expressed in Escherichia coli as a fusion protein, which oxidized GA(12) at C-20 to the C(19) compound GA(9), a precursor of bioactive GAs. RNA-blot analysis showed that the Cv20ox gene was expressed specifically in developing seeds. The gene was strongly expressed in the integument tissues, and it was also expressed weakly in inner seed tissues. In parthenocarpic fruits induced by 1-(2-chloro-4-pyridyl)-3-phenylurea treatment, the expression pattern of Cv20ox did not change, indicating that the GA 20-oxidase gene is expressed primarily in the maternal cells of developing seeds. The promoter of Cv20ox was isolated and fused to the beta-glucuronidase (GUS) gene. In a transient expression system, beta-glucuronidase staining was detectable only in the integument tissues of developing watermelon seeds.

Isolation and characterization of a cDNA encoding a high mobility group protein HMG-1 from Canavalia gladiata D.C

A cDNA clone encoding a HMG-1 protein from maturing seeds of Canavalia gladiata was isolated and characterized with respect to its sequence, genomic organization and the expression pattern in seeds. The predicted polypeptide had the characteristic conserved motifs of the HMG-1/2 protein including N-terminal basic region, one HMG-box and polyacidic carboxy terminus. Southern blot analysis suggested that the HMG-1 gene is a single copy gene. Northern blot analysis indicated that the HMG-1 gene was expressed both in maturing and germinated seeds.

Promoter structure and activity of type 1 rice metallothionein-like gene

A novel stress-inducible metallothionein-like gene from rice, designated as rgMT-1 (rice genomic metallothionein-like gene-1), was isolated and sequenced. From the sequence analysis of its 5'-flanking region, two putative TATA boxes, one CAAT box, and several short sequences homologous to regulatory cis-elements previously reported were identified. Two direct repeats, one 10 bp in length (CAAAATCAAA) and the other 11 bp (GTGAAAATACT), respectively, were also found. By transient GUS (beta-glucuronidase) assay, the expression of GUS, in vitro, was enhanced by the presence of the rgMT-1 intron. The critical region which controls the basal transcription was shown to lie between -73 and -36 upstream of rgMT-1, in which one of the two putative TATA boxes was located. The promoter activity was lost completely when both putative TATA boxes were deleted. This is the first report describing the genomic structure and regulation of a monocotyledonous metallothionein-like gene critical to the response of stress.

The 22 bp W1 element in the pea lectin promoter is necessary and, as a multimer, sufficient for high gene expression in tobacco seeds

The pea lectin (Psl) gene encodes an abundant seed protein. Its seed-specific expression pattern is conserved in transgenic tobacco plants. Progressive 5' promoter deletions resulted in a gradual decrease of transcriptional activity in tobacco seed. A fragment of 115 bp still conferred seed-specific expression albeit at a low level. This fragment contains a 22 bp element (W1), which has been demonstrated to be important for seed-specific expression when coupled as a trimer to a heterologous TATA box (de Pater et al., Plant Cell 5:877-886, 1993). Here we show that deletion of W1 in the natural promoter context resulted in a strongly decreased level of gene expression. A 4 bp mutation of W1 reduced the expression of truncated derivatives of the Psl promoter. A single copy of W1 coupled to the TATA box of the CaMV 35S promoter directed low gene expression in seeds and leaves. Multimerization enhanced the expression in seeds up to 100-fold, to levels found with the Psl promoter, whereas the expression level in leaves remained low. These results demonstrate that the W1 element is an essential control element in the Psl promoter. When taken out of its natural context and multimerized, it is sufficient for high expression in seeds.

Promoter regions of cysteine endopeptidase genes from legumes confer germination-specific expression in transgenic tobacco seeds

Cysteine endopeptidases, SH-EP from Vigna mungo and EP-C1 from Phaseolus vulgaris, act to degrade seed storage protein during seed germination. Using transgenic tobacco plants, expression of SH-EP and promoter activity of the EP-C1 gene were analyzed in transgenic tobacco plants. The promoters of the two genes in tobacco seeds showed germination-specific activation, although post-translational processing of SH-EP and regulatory regions of promoter of the gene for EP-C1 were found to differ between leguminous seeds and transgenic tobacco seeds.